Routing Fundamentals and Subnets Introduction to IT and Communications Technology CE00378-1.
Hierarchical IP addressing - Lagout Quick...Remember that you have a finite number of bits to work...
32
222 BSCI Quick Reference Sheets BSCI Quick Reference Sheets Advanced IP Addressing Issues Scalable Network Design A good network design is essential to a scalable network, so some basic design infor- mation is necessary. Networks can generally be broken into three functional layers: • Access —Where end users connect to the network. Switches (which can connect to access layer routers) are the typical network device at this layer, with VLANs, firewall, and access lists providing security and scalability. Host addressing is usu- ally Dynamic Host Configuration Protocol (DHCP). • Distribution —Access layer switches and routers aggregate to this layer. Routers and multilayer switches route between VLANs and to services that are used by many segments of the network (such as e-mail servers). This layer controls access to the core. • Core —This is the network backbone. It connects the different parts of the net- work. You generally find fast switches here, with as little in the way of security policies as possible. Core devices can be either fully meshed or in a hub-and-spoke with redundancy, as shown in the following figure. These components can be arranged in your network either by function or by geography: • Functional design —The network is divided up by department, division, or some other type of functional group. The distribution layer bounds each group and connects it to a common core. • Geographical design —A much more common design. The network is divided by location. The distribution layer allows access to groups that need to communicate and connects to a common core. Hierarchical IP addressing is an IP addressing plan that purposefully allows points of summarization. This takes a network, breaks it into subnets by location, then further subnets those addresses by location. In the following figure, the access layer routers can summarize their networks to the distribution layer, who can then combine all the subnets into one summary to the core. Scalable IP Addressing A well-designed network along with a hierarchical IP addressing plan gives your network: • Scalability —The network can grow to many users and many sites and still perform efficiently. • Predictability —Traffic patterns are predictable and all routers choose the best paths. • Flexibility —The impact of changes in the network are minimized, as the network has the ability to expand or contract. Additionally, hierarchical IP addressing allows: • Smaller routing tables because of summarization of networks • More efficient use of IP addresses because addresses can be assigned contiguously Core Distribution Access 10.1.0.0/16 10.1.1.0/24 10.1.2.0/24 10.1.1.0/27 10.1.1.32/27 10.1.1.64/27 10.1.2.0/28 10.1.2.16/28 10.1.2.32/28
Transcript of Hierarchical IP addressing - Lagout Quick...Remember that you have a finite number of bits to work...
222
BSCI Quick Reference Sheets
BS
CI Q
uic
k
Refe
ren
ce S
heets
Ad
van
ced
IP
Ad
dre
ssin
g Issu
es
Scala
ble
Netw
ork
De
sig
n
A g
ood
netw
ork
desi
gn is
ess
enti
al t
o a
scal
able
net
wor
k, s
o so
me
basi
c de
sign
info
r-m
atio
n is
nec
essa
ry. N
etw
orks
can
gen
eral
ly b
e br
oken
into
thr
ee f
unct
iona
l lay
ers:
•
Acc
ess
—W
here
end
use
rs c
onne
ct t
o th
e ne
twor
k. S
wit
ches
(w
hich
can
con
nect
to
acc
ess
laye
r ro
uter
s) a
re t
he t
ypic
al n
etw
ork
devi
ce a
t th
is la
yer,
wit
h V
LA
Ns,
fir
ewal
l, an
d ac
cess
list
s pr
ovid
ing
secu
rity
and
sca
labi
lity.
Hos
t ad
dres
sing
is u
su-
ally
Dyn
amic
Hos
t C
onfig
urat
ion
Prot
ocol
(D
HC
P).
•
Dis
trib
utio
n
—A
cces
s la
yer
swit
ches
and
rou
ters
agg
rega
te t
o th
is la
yer.
Rou
ters
an
d m
ulti
laye
r sw
itch
es r
oute
bet
wee
n V
LA
Ns
and
to s
ervi
ces
that
are
use
d by
m
any
segm
ents
of
the
netw
ork
(suc
h as
e-m
ail s
erve
rs).
Thi
s la
yer
cont
rols
acc
ess
to t
he c
ore.
•
Cor
e
—T
his
is t
he n
etw
ork
back
bone
. It
conn
ects
the
dif
fere
nt p
arts
of
the
net-
wor
k. Y
ou g
ener
ally
find
fas
t sw
itch
es h
ere,
wit
h as
litt
le in
the
way
of
secu
rity
po
licie
s as
pos
sibl
e. C
ore
devi
ces
can
be e
ithe
r fu
lly m
eshe
d or
in a
hub
-and
-spo
ke
wit
h re
dund
ancy
, as
show
n in
the
fol
low
ing
figur
e.T
hese
com
pone
nts
can
be a
rran
ged
in y
our
netw
ork
eith
er b
y fu
ncti
on o
r by
geo
grap
hy:
•
Func
tion
al
desi
gn
—T
he n
etw
ork
is d
ivid
ed u
p by
dep
artm
ent,
div
isio
n, o
r so
me
othe
r ty
pe o
f fu
ncti
onal
gro
up. T
he d
istr
ibut
ion
laye
r bo
unds
eac
h gr
oup
and
conn
ects
it t
o a
com
mon
cor
e.•
Geo
grap
hica
l des
ign
—A
muc
h m
ore
com
mon
des
ign.
The
net
wor
k is
div
ided
by
loca
tion
. The
dis
trib
utio
n la
yer
allo
ws
acce
ss to
gro
ups
that
nee
d to
com
mun
icat
e an
d co
nnec
ts t
o a
com
mon
cor
e.
Hie
rarc
hica
l IP
add
ress
ing
is a
n IP
add
ress
ing
plan
tha
t pu
rpos
eful
ly a
llow
s po
ints
of
sum
mar
izat
ion.
Thi
s ta
kes
a ne
twor
k, b
reak
s it
into
sub
nets
by
loca
tion
, the
n fu
rthe
r su
bnet
s th
ose
addr
esse
s by
loca
tion
. In
the
follo
win
g fig
ure,
the
acc
ess
laye
r ro
uter
s ca
n su
mm
ariz
e th
eir
netw
orks
to
the
dist
ribu
tion
laye
r, w
ho c
an t
hen
com
bine
all
the
subn
ets
into
one
sum
mar
y to
the
cor
e.
Scala
ble
IP
Ad
dre
ssin
g
A w
ell-d
esig
ned
netw
ork
alon
g w
ith a
hie
rarc
hica
l IP
addr
essi
ng p
lan
give
s yo
ur n
etw
ork:
•
Scal
abili
ty
—T
he n
etw
ork
can
grow
to m
any
user
s an
d m
any
site
s an
d st
ill p
erfo
rm
effic
ient
ly.
•
Pred
icta
bilit
y
—Tr
affic
pat
tern
s ar
e pr
edic
tabl
e an
d al
l rou
ters
cho
ose
the
best
pat
hs.
•
Flex
ibili
ty
—T
he im
pact
of
chan
ges
in t
he n
etw
ork
are
min
imiz
ed, a
s th
e ne
twor
k ha
s th
e ab
ility
to
expa
nd o
r co
ntra
ct.
Add
itio
nally
, hie
rarc
hica
l IP
addr
essi
ng a
llow
s:•
Smal
ler
rout
ing
tabl
es b
ecau
se o
f su
mm
ariz
atio
n of
net
wor
ks•
Mor
e ef
ficie
nt u
se o
f IP
add
ress
es b
ecau
se a
ddre
sses
can
be
assi
gned
con
tigu
ousl
y
Cor
e
Dis
trib
utio
n
Acc
ess
10.1
.0.0
/16
10.1
.1.0
/24
10.1
.2.0
/24
10.1
.1.0
/27
10.1
.1.3
2/27
10.1
.1.6
4/27
10.1
.2.0
/28
10.1
.2.1
6/28
10.1
.2.3
2/28
0910_BSCIssf.fm Page 222 Tuesday, September 9, 2003 8:24 AM
Advanced IP Addressing Issues
223
Vari
ab
le-L
en
gth
Su
bn
et
Maskin
g
Var
iabl
e-L
engt
h Su
bnet
Mas
king
(V
LSM
) in
volv
es u
sing
a s
ubne
t m
ask
that
giv
es y
ou
just
the
num
ber
of h
osts
nee
ded.
It
requ
ires
the
use
of
a cl
assl
ess
rout
ing
prot
ocol
(on
e th
at h
as a
fiel
d fo
r su
bnet
mas
k le
ngth
in it
s up
date
s.) I
n th
e pr
evio
us fi
gure
, the
net
wor
ks
on t
he r
ight
hav
e a
max
imum
of
14 h
osts
in e
ach
of t
hem
, whi
le t
he n
etw
orks
on
the
left
can
hav
e 30
hos
ts e
ach.
We
have
cho
sen
the
subn
et m
ask
base
d on
the
num
ber
of
host
s in
eac
h ne
twor
k.T
he f
orm
ula
to c
alcu
late
the
num
ber
of h
osts
allo
wed
by
a pa
rtic
ular
sub
net
mas
k is
2
n
– 2
, whe
re
n
is t
he n
umbe
r of
hos
t bi
ts in
the
sub
net.
The
for
mul
a to
cal
cula
te t
he
num
ber
of n
etw
orks
gai
ned
by s
ubne
ttin
g is
sim
ply
2
n
, whe
re
n
is th
e nu
mbe
r of
net
wor
k bi
ts in
add
itio
n to
the
cla
ssfu
l bit
s. T
he f
ollo
win
g ta
ble
show
s so
me
com
mon
sub
net
mas
ks, w
ith
the
num
ber
of h
osts
and
sub
nets
.
Calc
ula
tin
g V
LS
M IP
Ad
dre
sses
To p
lan
an I
P ad
dres
ses
sche
me
usin
g V
LSM
, fol
low
the
se g
ener
al s
teps
:1.
Beg
in b
y lo
okin
g at
the
netw
ork
that
you
use
to c
reat
e yo
ur s
ubne
ts a
nd d
eter
min
e ho
w m
any
bits
you
hav
e to
wor
k w
ith.
2.L
ook
at a
ll th
e se
gmen
ts t
hat
mus
t be
ass
igne
d IP
add
ress
es a
nd d
eter
min
e th
e m
ost
num
ber
of h
osts
any
net
wor
k re
quir
e.3.
Find
the
subn
et m
ask
for
the
larg
est s
ubne
t firs
t. T
o fig
ure
out h
ow m
any
bits
you
m
ust
allo
w f
or h
osts
, add
2 t
o th
e m
axim
um n
umbe
r of
hos
ts (
for
netw
ork
and
broa
dcas
t add
ress
es) a
nd th
en r
ound
up
to th
e ne
ares
t pow
er o
f 2. C
alcu
late
how
m
any
bits
equ
al t
hat
num
ber.
4.Fi
nd t
he s
ubne
t m
ask
for
the
num
ber
of h
ost
bits
nee
ded
by t
he la
rges
t ne
twor
k.
Or
use
the
prev
ious
tab
le t
o he
lp y
ou d
eter
min
e th
e ne
cess
ary
subn
et m
ask.
5.A
ssig
n th
e su
bnet
s ob
tain
ed b
y us
ing
this
sub
net m
ask
as n
eces
sary
to th
e la
rges
t sub
nets
.6.
Det
erm
ine
the
num
ber
of h
ost
bits
nee
ded
for
the
next
larg
est
subn
et(s
). T
ake
an
unus
ed s
ubne
t fr
om a
bove
and
sub
net
that
fur
ther
.7.
Con
tinu
e su
bnet
ting
the
sub
nets
for
the
sm
alle
r ne
twor
ks, u
ntil
you
have
IP
addr
esse
s fo
r al
l net
wor
ks.
Typi
cally
, poi
nt-t
o-po
int
links
are
ass
igne
d a
subn
et m
ask
of 2
55.2
55.2
55.2
52 (
a 30
bi
t m
ask,
als
o w
ritt
en a
s /3
0).
It is
rec
omm
ende
d th
at y
ou a
ssig
n ho
sts
wit
hin
a V
LA
N t
o th
e sa
me
subn
et.
Rem
embe
r th
at y
ou h
ave
a fin
ite
num
ber
of b
its
to w
ork
wit
h; t
he m
ore
subn
ets
you
need
, the
few
er h
osts
you
can
hav
e pe
r su
bnet
, and
vic
e ve
rsa.
Su
bn
ets
and
Ho
sts
Ori
gin
al N
etw
ork
: 172.1
6.0
.0, S
ub
net
Mask 2
55.2
55.0
.0 (
/16)
Su
bn
et
Mask
Ad
dit
ion
al
Su
bn
ets
Ho
sts
255.
255.
128.
0 (/
17)
232
,766
255.
255.
192.
0 (/
18)
416
,382
255.
255.
224.
0 (/
19)
881
90
255.
255.
240.
0 (/
20)
1640
94
255.
255.
248.
0 (/
21)
3220
46
255.
255.
252.
0 (/
22)
6410
22
255.
255.
254.
0 (/
23)
128
510
255.
255.
255.
0 (/
24)
256
254
255.
255.
255.
128
(/25
)51
212
6
255.
255.
255.
192
(/26
)1,
024
62
Ori
gin
al N
etw
ork
: 172.1
6.0
.0, S
ub
net
Mask 2
55.2
55.0
.0 (
/16)
Su
bn
et
Mask
Ad
dit
ion
al
Su
bn
ets
Ho
sts
255.
255.
255.
224
(/27
)2,
048
30
255.
255.
255.
240
(/28
)4,
096
14
255.
255.
255.
248
(/29
)8,
192
6
255.
255.
255.
252
(/30
)16
,384
2
Su
bn
ets
and
Ho
sts
(Co
nti
nu
ed)
0910_BSCIssf.fm Page 223 Tuesday, September 9, 2003 8:24 AM
224
BSCI Quick Reference Sheets
Ro
ute
Su
mm
ari
zati
on
Sum
mar
izat
ion
is, i
n a
sens
e, t
he o
ppos
ite
of s
ubne
ttin
g. W
hen
subn
etti
ng, y
ou m
ove
the
subn
et m
ask
boun
dary
to
the
righ
t, c
reat
ing
mor
e su
bnet
s. W
hen
sum
mar
izin
g,
you
mov
e th
e su
bnet
mas
k bo
unda
ry t
o th
e le
ft, t
hus
com
bini
ng s
ubne
ts.
Rou
te s
um-
mar
izat
ion
is a
nnou
ncin
g on
e ro
ute
that
enc
ompa
sses
man
y ne
twor
ks. F
or e
xam
ple,
if
you
wer
e in
a r
oom
wit
h 20
mem
bers
of
the
Smit
h fa
mily
, you
cou
ld e
ithe
r in
trod
uce
all 2
0 of
the
m in
divi
dual
ly o
r ju
st s
umm
ariz
e al
l 20
as “
the
Smit
h fa
mily
.” W
hich
w
ould
use
less
of
your
bra
in’s
reso
urce
s?Su
mm
ariz
atio
n us
es le
ss r
oute
r re
sour
ces
beca
use
you
have
few
er n
etw
orks
to
keep
in
the
rout
ing
tabl
e an
d to
ann
ounc
e to
you
r ne
ighb
ors.
Calc
ula
tin
g a
Su
mm
ary
Ad
dre
ss
1.T
he r
oute
s to
be
sum
mar
ized
mus
t sh
are
the
sam
e hi
gh-o
rder
bit
s.2.
Rou
tes
can
be s
umm
ariz
ed in
pow
ers
of 2
. If
you
mov
e th
e su
bnet
mas
k 1
bit
to
the
left
, tha
t su
mm
ariz
es 2
net
wor
ks. M
ovin
g it
3 b
its
to t
he le
ft s
umm
ariz
es 8
ne
twor
ks, e
tc.
3.O
rgan
ize
the
netw
orks
to b
e su
mm
ariz
ed n
umer
ical
ly a
nd w
rite
eac
h in
bin
ary
to
dete
rmin
e w
hat
high
-ord
er b
its
they
hav
e in
com
mon
.4.
Be
care
ful a
bout
incl
udin
g ro
utes
in t
he s
umm
ary
that
are
not
ass
igne
d to
you
. D
on’t
over
sum
mar
ize.
5.A
goo
d hi
erar
chic
al I
P ad
dres
sing
des
ign
allo
ws
for
max
imum
sum
mar
izat
ion.
6.Y
ou m
ust
use
a cl
assl
ess
rout
ing
prot
ocol
.7.
The
rou
ter
mus
t ba
se it
s ro
utin
g de
cisi
ons
on t
he e
ntir
e 32
-bit
IP
addr
ess
and
a pr
efix
leng
th o
f up
to
32 b
its.
Su
mm
ari
zati
on
Exam
ple
You
hav
e ne
twor
ks 1
0.1.
24.0
, 10.
1.25
.0, 1
0.1.
26.0
, and
10.
1.27
.0. T
he t
hird
oct
et is
w
here
you
can
sum
mar
ize,
bec
ause
it is
the
one
tha
t va
ries
. Tak
e a
look
at
the
thir
d oc
tet
in b
inar
y:24
--
0
0011
000
25
--
000
1100
126
--
0
0011
010
27
--
000
1101
1
Not
ice
that
the
firs
t si
x bi
ts a
re a
lway
s “0
0011
0” b
ut t
he la
st t
wo
bits
var
y be
twee
n 0
and
1. B
ecau
se t
he la
st t
wo
bits
incl
ude
all p
ossi
ble
com
bina
tion
s of
1 a
nd 0
, it
is s
afe
to s
umm
ariz
e th
ese
four
net
wor
ks in
to o
ne s
umm
ary
rout
e. C
onfig
ure
the
rout
er t
o ad
vert
ise
“10.
1.24
.0 2
55.2
55.2
52.0
”.T
he n
etw
ork
port
ion
of a
n IP
add
ress
is r
efer
red
to a
s th
e
prefi
x
.
Cla
ssle
ss In
terd
om
ain
Ro
uti
ng
(C
IDR
)
CID
R is
bas
ical
ly r
oute
sum
mar
izat
ion
done
on
Inte
rnet
rou
tes.
It
was
cre
ated
to
decr
ease
the
siz
e of
Int
erne
t ro
utin
g ta
bles
, and
mak
e be
tter
use
of
exis
ting
IP
addr
esse
s. S
ervi
ce p
rovi
ders
are
ass
igne
d a
bloc
k of
IP
addr
esse
s th
at t
hey
can
then
fur
-th
er s
ubne
t an
d as
sign
to
cust
omer
s. T
hese
add
ress
es c
ould
be
seve
ral c
onti
guou
s ne
t-w
orks
, or
just
a s
ubne
t of
a la
rger
net
wor
k. C
IDR
allo
ws
the
assi
gnm
ent
of a
ddre
ss
bloc
ks r
egar
dles
s of
the
cla
ssfu
l net
wor
k bo
unda
ry o
f th
e bl
ocks
. The
ser
vice
pro
vide
r th
en a
dver
tise
s to
the
Int
erne
t th
e su
mm
ary
rout
e fo
r it
s en
tire
blo
ck, i
nste
ad o
f ea
ch
cust
omer
’s s
ubne
t.
IP V
ers
ion
6
IP v
ersi
on 6
(IP
v6)
was
cre
ated
to
help
alle
viat
e th
e sh
orta
ge o
f IP
add
ress
es, a
nd t
o in
trod
uce
into
IP
addr
essi
ng t
he s
ame
mul
tipl
e le
vels
of
hier
arch
y as
fou
nd in
tel
e-ph
one
num
bers
. Ben
efits
of
IPv6
incl
ude
the
follo
win
g:•
Lar
ger
addr
ess
spac
e th
an I
Pv4—
128
vers
us 3
2 bi
ts.
•Si
mpl
er, m
ore
effic
ient
hea
der
than
IPv
4—40
byt
es lo
ng, 6
4-bi
t al
igne
d.•
Aut
ocon
figur
atio
n op
tion
s fo
r IP
v6 h
osts
.•
IP m
obili
ty c
apab
ility
bui
lt in
.•
Bro
adca
sts
are
not
used
, jus
t m
ulti
cast
and
any
cast
.•
IPSe
c av
aila
ble
on a
ll IP
v6 n
odes
.•
Cis
co I
OS
has
met
hods
for
eas
ing
tran
siti
on t
o IP
v6.
IPv6 A
dd
ress F
orm
at
•W
ritt
en in
hex
adec
imal
. Cas
e in
sens
itiv
e.•
A s
erie
s of
eig
ht 1
6-bi
t fie
lds,
sep
arat
ed b
y co
lons
.•
The
lead
ing
0s in
a fi
eld
are
opti
onal
(00
3c =
3c)
.•
Con
tigu
ous
field
s of
all
0s c
an b
e w
ritt
en a
s “:
:” (
two
colo
ns)
once
in a
n ad
dres
s.•
Allo
ws
mul
tipl
e le
vels
of
aggr
egat
ion.
Exam
ple
s o
f IP
v6 A
dd
resses
1234:5678:90ab:cdef:1001:2202:2bad:babe
abcd::1001 (equals abcd:0000:0000:0000:0000:0000:0000:1001)
a1:beef:3add:212::1 (equals 00a1:beef:3add:0212:0000:0000:0000:0001)
:: (equals all zeros)
0910_BSCIssf.fm Page 224 Tuesday, September 9, 2003 8:24 AM
Advanced IP Addressing Issues
225
•
Any
cast
—A
new
typ
e of
add
ress
ava
ilabl
e in
IPv
6. T
he s
ame
IP a
ddre
ss is
as
sign
ed t
o m
ulti
ple
devi
ces
that
hav
e th
e sa
me
func
tion
, suc
h as
a w
eb s
erve
r. D
evic
es s
end
a m
essa
ge t
o th
e an
ycas
t ad
dres
s an
d ro
uter
s ro
ute
it t
o th
e cl
oses
t de
vice
wit
h th
at a
ddre
ss.
•
Aut
ocon
figur
atio
n
—W
hen
a ho
st b
oots
up
it s
ends
a R
oute
r So
licit
atio
n (R
S).
The
rou
ter
resp
onds
wit
h a
Rou
ter
Adv
erti
sem
ent
cont
aini
ng a
64-
bit
netw
ork
prefi
x an
d de
faul
t ga
tew
ay. T
he h
ost
then
app
ends
its
MA
C a
ddre
ss t
o th
e pr
efix.
T
his
elim
inat
es t
he n
eed
for
DH
CP
or m
anua
l hos
t ad
dres
sing
.
IPv6 H
ead
er
•
Ver
sion
—4
bits
—C
onta
ins
the
num
ber
6 in
stea
d of
4.
•
Tra
ffic
Cla
ss
—8
bits
—Fo
r se
ttin
g qu
alit
y of
ser
vice
opt
ions
, sim
ilar
to t
ype
of
serv
ice
(ToS
) bi
ts in
IPv
4.•
Flow
Lab
el
—20
bit
s—Ta
gs a
flow
to
use
wit
h m
ulti
laye
r sw
itch
ing
and
for
fast
er
pack
et s
wit
chin
g•
Payl
oad
Len
gth
—16
bit
s—T
he t
otal
leng
th o
f th
e pa
cket
.•
Nex
t H
eade
r
—8
bits
—Te
lls w
hat
head
er f
ollo
ws
this
one
, in
the
data
por
tion
of
the
pack
et. C
ould
be
a L
ayer
4 h
eade
r or
an
exte
nsio
n he
ader
.•
Hop
Lim
it
—8
bits
—A
Tim
e-To
-Liv
e fie
ld. E
ach
rout
er d
ecre
men
ts th
is v
alue
by
1,
and
the
pack
et is
dro
pped
if it
rea
ches
0.
•
Sour
ce a
nd D
esti
nati
on A
ddre
ss
—12
8 bi
ts e
ach—
The
se fi
elds
giv
e th
e IP
add
ress
of
the
sou
rce
and
dest
inat
ion
devi
ce.
•
Ext
ensi
on H
eade
rs
—Si
ze v
arie
s. O
ptio
nal n
etw
ork
laye
r in
form
atio
n, u
sual
ly
read
onl
y by
the
des
tina
tion
dev
ice.
Tra
nsit
ion
ing
to
IP
v6 f
rom
IP
v4
•
Dua
l Sta
ck m
etho
d
—R
un b
oth
vers
ions
on
the
rout
ers
inte
rfac
es.
•
Man
ual t
unne
l
—U
se t
unne
ls t
o co
nnec
t ar
eas
of I
Pv6
sepa
rate
d by
are
as u
sing
IP
v4. T
unne
l end
poin
ts m
ust
be d
ual s
tack
ed; t
unne
l is
confi
gure
d m
anua
lly. S
et
up r
outi
ng t
o go
acr
oss
the
tunn
el b
etw
een
the
IPv6
net
wor
ks.
•
6to4
tun
nel
—R
oute
rs c
onfig
ure
this
aut
omat
ical
ly. E
ach
6 to
4 s
ite
is g
iven
a n
et-
wor
k ad
dres
s of
200
2 co
ncat
enat
ed w
ith
the
hex
equi
vale
nt o
f the
IPv4
add
ress
of
the
edge
rou
ter.
IPv6
tra
ffic
is e
ncap
sula
ted
in a
n IP
v4 p
acke
t ad
dres
sed
to t
he
othe
r ed
ge r
oute
r. T
hat
rout
er d
ecap
sula
tes
the
traf
fic a
nd f
orw
ards
it.
•
Rou
ting
IPv6
—IP
v6 is
sup
port
ed in
Enh
ance
d In
teri
or G
atew
ay R
outin
g Pr
otoc
ol
(EIG
RP)
, Ope
n Sh
orte
st P
ath
Firs
t (O
SPF)
, Rou
ting
Inf
orm
atio
n Pr
otoc
ol (
RIP
),
Inte
grat
ed In
term
edia
te S
yste
m-t
o-In
term
edia
te S
yste
m (I
S-IS
), an
d B
orde
r G
atew
ay
Prot
ocol
(BG
P).
Netw
ork
Ad
dre
ss T
ran
sla
tio
n (
NA
T)
NA
T in
volv
es a
net
wor
k de
vice
sw
appi
ng o
ne I
P ad
dres
s fo
r an
othe
r; it
cha
nges
the
so
urce
IP
addr
ess
of a
n ou
tgoi
ng p
acke
t an
d th
e de
stin
atio
n IP
add
ress
of
an in
com
ing
one.
Thi
s is
don
e to
hid
e IP
add
ress
es f
rom
the
out
side
wor
ld a
nd t
o en
able
mul
tipl
e de
vice
s to
use
the
sam
e IP
add
ress
es.
NA
T T
erm
ino
log
y
•
Insi
de in
terf
ace
—T
he r
oute
r’s in
terf
ace
that
poi
nts
to t
he in
side
of
your
com
pany
(E
1/0
on R
1).
•
Out
side
inte
rfac
e
—T
he r
oute
r’s in
terf
ace
that
poi
nts
to t
he r
est
of t
he w
orld
(S
0/0
on R
1).
•
Insi
de lo
cal I
P ad
dres
s
—T
he a
ctua
l IP
addr
ess
assi
gned
to
the
host
, usu
ally
a
priv
ate
addr
ess.
•
Insi
de g
loba
l IP
addr
ess
—W
hat
the
insi
de lo
cal I
P ad
dres
s ha
s be
en t
rans
late
d to
. T
his
is w
hat
outs
ide
host
s us
e as
the
IP
addr
ess
for
the
insi
de h
ost.
•
Out
side
glo
bal I
P ad
dres
s
—T
he a
ctua
l IP
addr
ess
of a
n ou
tsid
e ho
st.
•
Out
side
loca
l IP
addr
ess
—W
hat
your
net
wor
k se
es a
s th
e IP
add
ress
of
an o
utsi
de
host
. Thi
s co
uld
be a
tra
nsla
ted
addr
ess
or t
he t
rue
addr
ess
of t
he h
ost.
Exa
mpl
e
: In
the
figur
e, P
C1
has
an a
ddre
ss f
rom
the
pri
vate
add
ress
ing
spac
e. W
hen
it
send
s tr
affic
thr
ough
the
Int
erne
t to
PC
2, R
1 re
mov
es P
C1’
s IP
add
ress
(
insi
de lo
cal
) fr
om th
e pa
cket
hea
der
and
puts
in a
pub
lic a
ddre
ss (
insi
de g
loba
l
). P
C2
repl
ies
to th
at
publ
ic a
ddre
ss. R
1 th
en r
epla
ces
the
dest
inat
ion
addr
ess
wit
h th
e or
igin
al p
riva
te
addr
ess
and
send
s it
to
PC1.
Ver
sion
Traf
fic C
lass
Flo
w L
abel
Pay
load
Len
gth
Nex
t Hea
der
Hop
Lim
it
Sou
rce
Add
ress
Des
tinat
ion
Add
ress
Ext
ensi
on H
eade
r, If
Any
0910_BSCIssf.fm Page 225 Tuesday, September 9, 2003 8:24 AM
226
BSCI Quick Reference Sheets
The
add
ress
tha
t PC
1 ha
s fo
r PC
2 is
its
outs
ide
loca
l add
ress
. R2
mig
ht b
e do
ing
NA
T
also
, and
PC
2 m
ight
hav
e a
priv
ate
(out
side
glo
bal)
add
ress
tha
t is
nev
er s
een
by P
C1.
NA
T c
an b
e do
ne in
one
of
thre
e w
ays:
•A
lway
s tr
ansl
ate
the
sam
e in
side
add
ress
to
the
sam
e ou
tsid
e ad
dres
s.•
Pick
an
outs
ide
addr
ess
from
a p
ool o
f ad
dres
ses
whe
n an
insi
de a
ddre
ss n
eeds
tr
ansl
atin
g.•
Tra
nsla
te a
ll in
side
add
ress
es t
o th
e sa
me
outs
ide
addr
ess
(cal
led
over
load
ing
the
ou
tsid
e ad
dres
s).
NA
T C
on
fig
ura
tio
n w
ith
Access L
ists
an
d M
ult
iple
Po
ols
Iden
tify
wha
t tr
affic
to
tran
slat
e w
ith
a st
anda
rd o
r ex
tend
ed a
cces
s lis
t. M
ulti
ple
acce
ss li
sts
can
be u
sed
if d
iffe
rent
tra
ffic
mus
t be
tra
nsla
ted
to d
iffe
rent
add
ress
es.
Stan
dard
acc
ess
lists
tran
slat
e tr
affic
bas
ed o
n so
urce
add
ress
; ext
ende
d ac
cess
list
s ca
n tr
ansl
ate
traf
fic b
ased
on
sour
ce, d
esti
nati
on, a
nd o
ther
info
rmat
ion.
P
erm
it
traf
fic th
at
shou
ld b
e tr
ansl
ated
.C
reat
e th
e po
ols
of o
utsi
de a
ddre
sses
to u
se fo
r tr
ansl
atio
n. T
he c
omm
and
for
this
is a
s fo
llow
s:
ip nat pool
[
pool name
] [
star
ting ip address
] [
ending ip address
]
[
prefix-length
<
prefix len
gth
>
|
netmask
<
subnet mask
>]
Nex
t, li
nk t
his
pool
to
the
acce
ss li
st u
sing
the
fol
low
ing
com
man
d:
ip nat inside source list
[
ACL number]
pool
[
pool name
]
Las
tly,
spe
cify
whi
ch in
terf
aces
are
insi
de a
nd w
hich
are
out
side
one
s. T
he c
omm
and,
at
the
inte
rfac
e co
nfig
mod
e, is
iiiipppp nnnnaaaatttt iiiinnnnssssiiiiddddeeee
or
iiiipppp nnnnaaaatttt oooouuuuttttssssiiiiddddeeee
NA
T w
ith
Ro
ute
Map
s
Test
the
actio
ns o
f NA
T w
ith th
e
show
ip n
at tr
ansl
atio
ns
com
man
d. W
hen
doin
g N
AT
w
ith
just
acc
ess
lists
, thi
s co
mm
and
show
s on
ly t
he s
ourc
e an
d de
stin
atio
n ad
dres
ses
(
sim
ple
entr
ies
). T
o se
e po
rt a
nd p
roto
col i
nfor
mat
ion
(
exte
nded
ent
ries
) al
so, e
ithe
r us
e N
AT
wit
h ov
erlo
adin
g or
use
a r
oute
map
to
spec
ify
traf
fic t
o be
tra
nsla
ted.
Rou
te m
aps
are
desc
ribe
d in
det
ail i
n a
late
r st
udy
shee
t. L
inki
ng t
he a
cces
s lis
ts t
o a
rout
e m
ap a
nd u
sing
tha
t to
spe
cify
tra
ffic
to b
e tr
ansl
ated
giv
e yo
u an
ext
ende
d tr
ansl
atio
n ta
ble.
NA
T T
ran
slat
ion
Tab
le W
ith
ou
t R
ou
te M
aps
NA
T T
ran
slat
ion
Tab
le w
ith
Ro
ute
Map
s
Cre
ate
acce
ss li
sts
and
addr
ess
pool
s as
bef
ore.
The
n, c
reat
e ro
ute
map
s an
d re
fer
to
the
acce
ss li
sts
in t
he r
oute
map
s. N
ext,
link
the
rou
te m
aps
to t
he p
ools
wit
h th
e fo
l-lo
win
g co
mm
and:
ip nat inside source route-map
<
route map name
>
pool
<
pool name
>
Un
ders
tan
din
g IP
Ro
uti
ng
Sta
tic R
ou
tin
g
The
eas
iest
and
mos
t st
raig
htfo
rwar
d w
ay t
o pu
t a
rout
e in
to t
he r
outi
ng t
able
is t
o cr
eate
a s
tati
c ro
ute.
Router(config)#
ip route
{
prefix
} {
mask
} {
next-hop
} [
distance
]
[
permanent
]
The
nex
t ro
uter
alo
ng t
he p
ath
can
be id
enti
fied
by a
n ad
jace
nt I
P ad
dres
s or
by
a co
nnec
ting
poi
nt-t
o-po
int
inte
rfac
e.
PC
1
R1
PC
2
R2
Inte
rnet
E1/
0E
0/0
S0/
0S
1/1
Pro
Insid
e G
lob
al
Insid
e L
oca
l O
uts
ide
Lo
ca
lO
uts
ide
Glo
ba
l
---
63.1
.1.1
10.1
.1.1
---
---
Pro
Insid
e G
lob
al
Insid
e L
oca
l O
uts
ide
Lo
ca
lO
uts
ide
Glo
ba
l
udp
63.1
.1.1
:201
010
.1.1
.1:2
010
82.3
.1.2
:69
82.3
.1.2
:69
0910_BSCIssf.fm Page 226 Tuesday, September 9, 2003 8:24 AM
Understanding IP Routing
227
Stat
ic r
oute
s ha
ve a
def
ault
adm
inis
trat
ive
dist
ance
of
1. T
o cr
eate
a r
oute
wit
h a
high
er
adm
inis
trat
ive
dist
ance
(A
D),
incl
ude
a va
lue
for
dist
ance
. A s
tati
c ro
ute
wit
h a
very
hi
gh A
D, s
o hi
gh t
hat
the
rout
e is
not
use
d as
long
as
a ro
ute
is le
arne
d fr
om a
rou
ting
pr
otoc
ol, i
s ca
lled
a
float
ing
stat
ic r
oute
.T
he p
erm
anen
t ke
ywor
d ca
uses
the
rou
te t
o re
mai
n in
the
rou
ting
tab
le, e
ven
if t
he
next
hop
is lo
st.
Stat
ic r
outi
ng d
oes
not
adju
st t
o ne
twor
k ch
ange
s, s
tati
c ro
utin
g re
quir
es t
ime
to m
ain-
tain
in a
gro
win
g ne
twor
k, a
nd s
tati
c ro
utin
g do
esn’
t sc
ale
wel
l (ea
ch n
ew b
ranc
h of
fice
resu
lts
in a
new
sta
tic
rout
e on
all
othe
r ro
uter
s).
Stat
ic r
oute
s do
n’t
com
mun
icat
e in
form
atio
n to
nei
ghbo
ring
rou
ters
. An
impo
rtan
t po
int t
o re
mem
ber
abou
t sta
tic
rout
es is
that
for
rout
ers
to c
omm
unic
ate,
the
neig
hbor
ro
uter
nee
ds a
rec
ipro
cal r
oute
bac
k.St
atic
rou
tes
are
appr
opri
ate
whe
n•
The
re is
a s
ingl
e ex
it p
ath
from
a r
oute
r.•
The
ban
dwid
th r
equi
red
to s
uppo
rt a
rou
ting
pro
toco
l is
unac
cept
able
.•
The
mem
ory
and
cent
ral p
roce
ssin
g un
it (
CPU
) re
sour
ces
requ
ired
to
supp
ort
a ro
utin
g pr
otoc
ol a
re u
nacc
epta
ble.
Th
e D
efa
ult
Ro
ute
The
rou
te to
0.0
.0.0
/0 is
a s
peci
al r
oute
—th
e de
faul
t rou
te. A
def
ault
rout
e is
a p
ath
to
“eve
ryw
here
els
e.”
If s
ever
al p
aths
sho
uld
be c
onsi
dere
d, th
e ro
uter
cho
oses
the
path
with
th
e lo
nges
t pre
fix m
atch
, so
the
defa
ult i
s al
so k
now
n as
the
“pat
h of
last
res
ort.”
A ty
pica
l br
anch
offi
ce c
onfig
urat
ion,
with
ser
ial0
lead
ing
back
to H
Q, m
ight
look
like
the
follo
win
g:Router(config)# ip route 0.0.0.0 0.0.0.0 serial0
Dyn
am
ic R
ou
tin
gD
ynam
ic r
outi
ng p
roto
cols
aut
omat
ical
ly p
ick
the
best
pat
h of
man
y an
d ad
just
to a
new
pa
th a
s ci
rcum
stan
ces
chan
ge, b
ut t
hey
invo
lve
mor
e ad
vanc
ed u
pkee
p an
d ov
erhe
ad.
IP r
outi
ng p
roto
cols
incl
ude
the
follo
win
g:•
RIP
(v1
and
v2)
•In
teri
or G
atew
ay R
outi
ng P
roto
col (
IGR
P)•
EIG
RP
•O
SPF
•IS
-IS
•B
GP
On
Dem
an
d R
ou
tin
gO
n D
eman
d R
outi
ng (
OD
R)
uses
CD
P in
form
atio
n to
bui
ld r
outi
ng t
able
s.T
he C
isco
Dis
cove
ry P
roto
col (
CD
P) h
as t
he f
ollo
win
g ch
arac
teri
stic
s:•
Run
s au
tom
atic
ally
.•
Is g
loba
lly d
isab
led
wit
h th
e fo
llow
ing
com
man
d:Router(config)#no cdp run
•Is
dis
able
d on
an
inte
rfac
e w
ith
the
follo
win
g:Router(config-if)#no cdp enable
•Se
nds
out u
pdat
es e
very
60
seco
nds
and
hold
s up
date
s fo
r 18
0 se
cond
s. T
he ti
mer
is
cha
nged
usi
ng t
he f
ollo
win
g co
mm
and:
Router(config)#cdp timer seconds
OD
R h
as t
he f
ollo
win
g ch
arac
teri
stic
s:•
Is a
ppro
pria
te o
nly
for
hub
and
spok
e.•
Spok
es s
end
clas
sles
s co
nnec
ted
rout
es t
o hu
b ro
uter
.•
Hub
rou
ter
send
s de
faul
t ro
ute
to e
ach
spok
e ro
uter
.•
No
spok
e co
nfigu
rati
on is
req
uire
d (C
DP
mus
t be
run
ning
bet
wee
n ea
ch s
poke
an
d th
e hu
b).
•E
nabl
ing
any
rout
ing
prot
ocol
on
spok
e ro
uter
dis
able
s O
DR
.
R1
R2#
sho
w ip
ro
ute
o 0.
0.0.
0/0
(160
/1)
via
192.
168.
3.1,
00:
00:3
2, S
eria
l0C
192
.168
.1.0
is d
irect
ly c
onne
cted
, Eth
erne
t0
R3#
sho
w ip
ro
ute
o 0.
0.0.
0/0
(160
/1)
via
192.
168.
3.5,
00:
00:3
9, S
eria
l0C
192
.168
.2.0
is d
irect
ly c
onne
cted
, Eth
erne
t0
R1(
conf
ig)#
rou
ter
od
rR
1(co
nfig
)#en
dR
1#sh
ow
ip r
ou
teo
192.
168.
1.0/
24 (
160/
1) v
ia 1
92.1
68.3
.2, 0
0:00
:28,
Ser
ial0
o 19
2.16
8.2.
0/24
(16
0/1)
via
192
.168
.3.6
, 00:
00:0
1, S
eria
l0
R2
R3
192.
168.
1.0/
2419
2.16
8.2.
0/24
0910_BSCIssf.fm Page 227 Tuesday, September 9, 2003 8:24 AM
228 BSCI Quick Reference Sheets
•Is
ena
bled
on
hub
wit
h th
e co
mm
and:
Router(config)#router odr
•H
as a
n A
D o
f 16
0; t
he m
etri
c is
alw
ays
1.
Cla
ssfu
l IP
Ro
uti
ng
Cla
ssfu
l R
ou
tin
gT
here
are
tw
o cl
assf
ul I
P ro
utin
g pr
otoc
ols:
•R
IPv1
•IG
RP
Cla
ssfu
l rou
ting
pro
toco
ls d
o no
t inc
lude
a s
ubne
t mas
k in
rou
ting
upd
ates
. The
refo
re,
the
prefi
x le
ngth
is a
ssum
ed b
y th
e re
ceiv
er t
o be
eit
her:
•T
he s
ame
as t
he r
ecei
ving
inte
rfac
e, if
in t
he s
ame
clas
sful
net
wor
k.•
Sum
mar
ized
to
the
clas
sful
mas
k, if
in a
noth
er c
lass
ful n
etw
ork.
An
exam
ple
of R
IP a
dver
tise
men
ts is
sho
wn
to il
lust
rate
how
sub
net
mas
ks a
re
assu
med
.
The
se a
ssum
ptio
ns le
ad t
o th
e tw
o ru
les
of c
lass
ful n
etw
ork
desi
gn:
•A
ll su
bnet
s of
a c
lass
ful n
etw
ork
mus
t us
e th
e sa
me
mas
k.•
Eac
h cl
assf
ul n
etw
ork
mus
t be
con
tigu
ous.
An
easy
way
to
appr
ecia
te t
he is
sues
wit
h cl
assf
ul r
outi
ng is
to
cons
ider
how
the
net
-w
ork
in t
he f
ollo
win
g ex
ampl
e fu
ncti
ons
whe
n th
e in
teri
or li
nk g
oes
dow
n. R
1
rece
ives
a r
oute
to
192.
168.
1.0
from
R2
and
R3
and,
the
refo
re, l
oad
bala
nces
ove
r tw
o pa
ths
to r
each
192
.168
.1.6
5.
The
pro
blem
is th
at w
hen
the
inte
rior
link
goe
s do
wn,
R1
does
not
rec
eive
info
rmat
ion
abou
t th
e ch
ange
d to
polo
gy b
ecau
se o
f th
e cl
assf
ul s
umm
ariz
atio
n. R
1 co
ntin
ues
to
load
bal
ance
, and
the
refo
re, o
nly
half
the
tra
ffic
reac
hes
192.
168.
1.65
.
Th
e ip
cla
ssle
ss C
om
man
dRouter(config)# ip classless
The
ip c
lass
less
com
man
d be
cam
e a
defa
ult
in v
ersi
on 1
2.0
of t
he I
OS.
Wit
hout
the
co
mm
and,
a r
oute
r op
erat
ing
clas
sful
ly a
nd n
eedi
ng to
rou
te tr
affic
to a
noth
er lo
cati
on
with
in th
e sa
me
clas
sful
net
wor
k ch
ecks
the
rout
ing
tabl
e fo
r sp
ecifi
c ro
utin
g in
form
atio
n an
d, if
not
fou
nd, d
rops
the
tra
ffic.
Thi
s m
akes
sen
se b
ecau
se c
lass
ful n
etw
orks
mus
t be
bui
lt w
ith
all s
ubne
ts c
onti
guou
s.W
ith
ip c
lass
less
, the
rou
ter
cons
ider
s ro
utes
insi
de t
he c
lass
ful n
etw
ork,
and
if n
o ro
ute
is f
ound
, the
rou
ter
can
reso
rt t
o le
ss s
peci
fic r
oute
s in
clud
ing
the
defa
ult.
Cla
ssle
ss IP
Ro
uti
ng
Pro
toco
ls
Cla
ssle
ss R
ou
tin
gC
lass
less
IP
rout
ing
prot
ocol
s in
clud
e R
IPv2
, EIG
RP,
OSP
F, a
nd I
S-IS
. Cla
ssle
ss r
out-
ing
prot
ocol
s in
clud
e a
subn
et m
ask
in r
outi
ng u
pdat
es, s
o th
ey s
moo
thly
han
dle
dis-
cont
iguo
us s
ubne
ts a
nd s
itua
tion
s of
var
iabl
e le
ngth
sub
net
mas
k. B
ecau
se o
f cl
assl
ess
rout
ing’
s ab
ility
to
cons
erve
add
ress
spa
ce a
nd t
o ha
ndle
any
add
ress
spa
ce, c
lass
less
ro
utin
g is
gen
eral
ly a
ssum
ed t
o be
tak
ing
plac
e in
mod
ern
IP n
etw
orks
.
R1
R2
R3
192.
168.
1.0/
2719
2.16
8.1.
64/2
7
10.1
.1.4
/30
10.1
.1.0
/30
192.
168.
1.32
/27
192.
168.
1.0,
1 H
op19
2.16
8.1.
0, 1
Hop
192.
168.
1.0,
1 H
op10
.0.0
.0, 1
Hop
192.
168.
1.64
, 1 H
op10
.0.0
.0, 1
Hop
R1
R2
R3
192.
168.
1.0/
2719
2.16
8.1.
64/2
7
10.1
.1.4
/30
10.1
.1.0
/30
Dow
n!
192.
168.
1.0,
1 H
op19
2.16
8.1.
0, 1
Hop
0910_BSCIssf.fm Page 228 Tuesday, September 9, 2003 8:24 AM
Comparing RIP and IGRP 229
Au
to-S
um
mary
Cla
ssle
ss r
outi
ng s
uppo
rts
the
use
of a
rbit
rary
sum
mar
y ro
utes
to
redu
ce t
he r
outi
ng
tabl
e co
mpl
exity
. Sum
mar
izat
ion
redu
ces
the
size
and
am
ount
of r
outin
g pr
otoc
ol tr
affic
an
d th
e am
ount
of
syst
em r
esou
rces
use
d to
mai
ntai
n a
rout
ing
prot
ocol
and
hid
es
(hop
eful
ly!)
uni
mpo
rtan
t ne
twor
k de
tails
. Sum
mar
izat
ion
is g
ener
ally
a g
ood
idea
so
RIP
v2 a
nd E
IGR
P at
tem
pt t
o au
tom
atic
ally
sum
mar
ize
at a
logi
cal p
lace
—th
e jo
inin
g of
cla
ssfu
l net
wor
ks. T
he p
robl
em is
tha
t th
is b
reak
s di
scon
tigu
ous
netw
orks
and
end
s up
tur
ned
off
in m
any
curr
ent
inst
alla
tion
s. T
he e
xam
ple
show
s th
e di
stri
buti
on o
f R
IPv2
rou
tes
wit
h au
tom
atic
cla
ssfu
l sum
mar
izat
ion
in p
lace
. Not
ice
that
the
sub
net
mas
ks a
re in
clud
ed in
eac
h up
date
, but
tha
t R
1 st
ill r
ecei
ves
the
sam
e ro
ute
to
192.
168.
1.0/
24 f
rom
R2
and
R3
and,
the
refo
re, l
oad
bala
nces
to
reac
h an
add
ress
in
the
Cla
ss C
net
wor
k. (
All
traf
fic e
vent
ually
get
s th
roug
h, a
ltho
ugh
not
alw
ays
alon
g th
e sh
orte
st p
ath.
)
No
Au
to-S
um
mary
Aut
omat
ic s
umm
ariz
atio
n is
dis
able
d un
der
the
rout
ing
proc
ess
wit
h th
e no
aut
o-su
mm
ary
com
man
d:Router(config-router)# no auto-summary
Wit
h au
to-s
umm
ary
off,
com
plet
e ta
bles
are
now
dis
trib
uted
. Thi
s m
eans
tha
t R
1 ta
kes
the
shor
test
pat
h to
rea
ch a
ny d
esti
nati
on.
The
fol
low
ing
diag
ram
illu
stra
tes
the
issu
e w
ith
sum
mar
izat
ion.
In th
is c
ase,
RIP
is a
utom
atic
ally
sum
mar
izin
g at
cla
ssfu
l net
wor
k bo
unda
ries
. The
link
be
twee
n R
2 an
d R
3 is
bro
ken,
but
eac
h de
vice
sti
ll ad
vert
ises
the
cla
ssfu
lly c
ompl
ete
netw
ork.
The
res
ult
is t
hat
R1
load
bal
ance
s to
192
.168
.1.6
5 ov
er t
he p
erce
ived
tw
o eq
ual-
cost
pat
hs, r
esul
ting
in 5
0 pe
rcen
t pa
cket
loss
.W
hen
auto
mat
ic s
umm
ariz
atio
n is
tur
ned
off,
thi
s is
sue
is r
epai
red
beca
use
each
sp
ecifi
c ro
ute
is c
omm
unic
ated
.T
he a
dvan
tage
s of
cla
ssle
ss r
outi
ng p
roto
cols
are
as
follo
ws:
•Su
ppor
t fo
r V
aria
ble-
Len
gth
Subn
et M
aski
ng (
VL
SM),
whi
ch is
mor
e ef
ficie
nt o
f ad
dres
s sp
ace
•Su
ppor
t fo
r cl
assl
ess
inte
rdom
ain
rout
ing
(CID
R),
or
sum
mar
ies
to b
lock
s of
cl
assf
ul n
etw
orks
Co
mp
ari
ng
RIP
an
d IG
RP
IGR
PR
IP w
as t
he o
rigi
nal r
outi
ng p
roto
col,
but
was
des
igne
d fo
r a
tim
e w
hen
WA
N li
nks
wer
e co
mm
only
56
K. B
y th
e la
te 1
980s
, it w
as r
ecog
nize
d th
at a
mor
e ad
vanc
ed r
outi
ng
prot
ocol
was
nee
ded.
Inte
rior
Gat
eway
Rou
ting
Pro
toco
l (IG
RP)
was
not
tha
t pr
otoc
ol—
OSP
F w
as, b
ut it
w
asn’
t co
min
g fa
st e
noug
h. C
isco
inve
nted
IG
RP
as a
n in
teri
m s
olut
ion
and
care
fully
ad
dres
sed
the
two
larg
est
prob
lem
s w
ith
RIP
:•
RIP
put
s ou
t to
o m
uch
broa
dcas
t tr
affic
.•
RIP
ass
umes
all
links
are
the
sam
e sp
eed.
Cis
co a
ddre
ssed
the
issu
e of
tra
ffic
volu
me
by d
ecre
asin
g th
e fr
eque
ncy
of r
outi
ng
upda
tes—
IGR
P se
nds
out
a co
py o
f it
’s ro
utin
g ta
ble
ever
y 90
sec
onds
inst
ead
of e
very
30
sec
onds
like
RIP
. Unf
ortu
nate
ly, t
he u
pdat
es a
re b
road
cast
just
like
RIP
.
R1
R2
R3
192.
168.
1.0/
2719
2.16
8.1.
64/2
7
10.1
.1.4
/30
10.1
.1.0
/30
192.
168.
1.32
/30
192.
168.
1.0/
24, 1
Hop
192.
168.
1.0/
24, 1
Hop
192.
168.
1.0/
27, 1
Hop
10.0
.0.0
/8, 1
Hop
192.
168.
1.64
/27,
1 H
op10
.0.0
.0/8
, 1 H
op
R1
R2
R3
192.
168.
1.0/
2719
2.16
8.1.
64/2
7
10.1
.1.4
/30
10.1
.1.0
/30
Dow
n
192.
168.
1.0/
24, 1
Hop
192.
168.
1.0/
24, 1
Hop
0910_BSCIssf.fm Page 229 Tuesday, September 9, 2003 8:24 AM
230 BSCI Quick Reference SheetsIG
RP
uses
a c
ompl
ex m
etri
c th
at in
clud
es a
s va
riab
les
the
follo
win
g:•
Ban
dwid
th•
Del
ay•
Loa
d (n
ot u
sed
by d
efau
lt)
•R
elia
bilit
y (n
ot u
sed
by d
efau
lt)
Max
imum
tra
nsm
issi
on u
nit
(MT
U)
is t
rack
ed; t
his
was
mea
nt t
o al
low
pat
h M
TU
di
scov
ery,
but
it w
as n
ever
impl
emen
ted.
Hop
cou
nt is
als
o tr
acke
d, b
ut s
tric
tly
as a
lo
op r
ecog
niti
on t
echn
ique
.IG
RP
is a
Cis
co p
ropr
ieta
ry c
lass
ful I
P ro
utin
g pr
otoc
ol. B
y de
faul
t, R
IP w
ill b
e en
able
d on
all
inte
rfac
es t
hat
fall
wit
hin
the
netw
orks
spe
cifie
d in
the
net
wor
k co
mm
and.
Une
qual
cos
t lo
ad b
alan
cing
is a
uni
que
feat
ure
of I
GR
P an
d E
nhan
ced
IGR
P (E
IGR
P). W
hen
uneq
ual c
ost
load
bal
anci
ng is
act
ive,
the
bes
t m
etri
c to
a r
oute
is m
ul-
tipl
ied
by a
who
le-n
umbe
r va
rian
ce. A
ny p
ath
low
er th
an th
e pr
oduc
t is
load
-bal
ance
d pr
opor
tion
ally
.
RIP
Vers
ion
1R
IP v
1 is
a s
tand
ard-
base
d (R
FC 1
058)
cla
ssfu
l rou
ting
pro
toco
l tha
t us
es h
op c
ount
as
its
met
ric.
RIP
bro
adca
sts
a co
py o
f it
s ta
ble
ever
y 30
sec
onds
and
, lik
e al
l oth
er I
P ro
utin
g pr
otoc
ols
on a
Cis
co r
oute
r, su
ppor
ts e
qual
cos
t lo
ad b
alan
cing
.
RIP
Vers
ion
2R
IP v
2 is
a s
tand
ards
-bas
ed (
RFC
172
1, 1
722,
and
245
3) c
lass
less
rou
ting
pro
toco
l th
at u
ses
hop
coun
t as
its
met
ric.
Ver
sion
2 a
ddre
sses
sev
eral
of t
he is
sues
wit
h V
ersi
on 1
:•
Ver
sion
2 is
cla
ssle
ss (
VL
SM).
•V
ersi
on 2
sup
port
s ro
ute
sum
mar
izat
ion
and
, by
defa
ult,
auto
mat
ical
ly s
umm
ariz
es
at c
lass
ful n
etw
ork
boun
dari
es. A
utom
atic
sum
mar
izat
ion
can
be d
isab
led,
and
m
anua
l sum
mar
izat
ion
confi
gure
d.•
Ver
sion
2 u
ses
mul
tica
sts
inst
ead
of b
road
cast
s•
Ver
sion
2 a
llow
s fo
r au
then
tica
tion
(pl
ain
text
or
MD
5).
RIP
is c
onfig
ured
by
ente
ring
the
RIP
rou
ter
confi
gura
tion
mod
e an
d id
enti
fyin
g th
e cl
assf
ul n
etw
orks
wit
hin
whi
ch it
sho
uld
run.
All
inte
rfac
es o
n th
e ro
uter
in t
he
assi
gned
net
wor
ks r
un R
IP.
Router(config)# router rip
Router(config-router)# network 192.168.1.0
By
defa
ult,
RIP
sen
ds v
ersi
on 1
and
rec
eive
s ve
rsio
n 1
and
2 ro
utes
. To
confi
gure
RIP
to
run
onl
y ve
rsio
n 2
use
the
vers
ion
com
man
d.Router(config-router)# version 2
Con
figur
e sp
ecifi
c in
terf
aces
to
run
eith
er v
ersi
on 1
or
2 or
bot
h us
ing
the
ip r
ip s
end
or ip
rip
rec
eive
com
man
ds.
Router(config-router)# ip rip send version 2
Router(config-router)# ip rip receive version 2
Fina
lly, c
onfig
ure
a su
mm
ary
rout
e ou
t a
part
icul
ar in
terf
ace
usin
g th
e ip
sum
mar
y-ad
dres
s ri
p co
mm
and.
Of
cour
se, a
utom
atic
sum
mar
izat
ion
is u
sual
ly d
isab
led
also
(n
o au
to-s
umm
ary)
. The
fol
low
ing
exam
ple
adve
rtis
es a
def
ault
rou
te o
ut e
ther
net0
an
d a
sum
mar
y ro
ute
172.
16.1
04.0
/22
out
seri
al0.
Router(config)# int e0
Router(config-if)# ip summary-address rip 0.0.0.0 0.0.0.0
Router(config)# int s0
Router(config-if)# ip summary-address rip 172.16.104.0 255.255.252.0
IP R
ou
tin
g P
roto
co
ls
Ad
min
istr
ati
ve D
ista
nce
Cis
co r
oute
rs a
re c
apab
le o
f sup
port
ing
seve
ral I
P ro
utin
g pr
otoc
ols
conc
urre
ntly
. Whe
n id
enti
cal p
refix
es a
re d
isco
vere
d fr
om t
wo
or m
ore
sepa
rate
pro
toco
ls, a
dmin
istr
ativ
e di
stan
ce (
AD
) is
use
d to
dis
crim
inat
e be
twee
n th
e pa
ths.
AD
is r
eally
a p
oor
choi
ce o
f w
ords
—tr
ustw
orth
ines
s w
ould
be
a be
tter
nam
e. R
oute
rs u
se p
aths
wit
h th
e lo
wer
AD
.T
he f
ollo
win
g ta
ble
lists
the
def
ault
val
ues
for
vari
ous
rout
ing
prot
ocol
s. O
f co
urse
, yo
u ha
ve s
ever
al w
ays
to c
hang
e A
D f
or a
rou
ting
pro
toco
l or
for
a sp
ecifi
c ro
ute.
Info
rmati
on
So
urc
eA
D
Con
nect
ed0
Stat
ic1
Ext
erna
l BG
P20
Inte
rnal
EIG
RP
90
IGR
P10
0
OSP
F11
0
IS-I
S11
5
RIP
120
OD
R16
0
0910_BSCIssf.fm Page 230 Tuesday, September 9, 2003 8:24 AM
EIGRP 231
Bu
ild
ing
th
e R
ou
tin
g T
ab
leT
he r
oute
r bu
ilds
its
rout
ing
tabl
e by
rul
ing
out
inva
lid r
oute
s an
d ca
refu
lly c
onsi
deri
ng
the
rem
aini
ng a
dver
tise
men
ts. T
he p
roce
dure
is a
s fo
llow
s:•
For
each
rou
te r
ecei
ved,
ver
ify
the
next
hop
. If
inva
lid, d
isca
rd t
he r
oute
.•
If m
ore
than
one
spe
cific
val
id r
oute
is a
dver
tise
d by
a r
outi
ng p
roto
col,
choo
se
the
path
wit
h th
e lo
wes
t m
etri
c.•
If m
ore
than
one
spe
cific
val
id r
oute
is a
dver
tise
d by
dif
fere
nt r
outi
ng p
roto
cols
, ch
oose
the
pat
h w
ith
the
low
est
AD
.•
Rou
tes
are
cons
ider
ed id
enti
cal i
f th
ey a
dver
tise
the
sam
e pr
efix
and
mas
k, s
o 19
2.16
8.0.
0/16
and
192
.168
.0.0
/24
are
sepa
rate
pat
hs a
nd a
re e
nter
ed in
to t
he
rout
ing
tabl
e se
para
tely
.
Co
mp
ari
ng
Ro
uti
ng
Pro
toco
lsG
ener
ical
ly, t
wo
thin
gs s
houl
d al
way
s be
con
side
red
in c
hoos
ing
a ro
utin
g pr
otoc
ol:
fast
con
verg
ence
spe
ed a
nd s
uppo
rt fo
r V
LSM
. EIG
RP,
OSP
F, a
nd IS
-IS
mee
t the
se c
rite
ria.
EIG
RP
is C
isco
pro
prie
tary
, but
sim
ple
to c
onfig
ure
and
supp
ort.
OSP
F is
sta
ndar
ds
base
d, b
ut d
iffic
ult
to im
plem
ent
and
supp
ort.
IS-
IS is
an
OSI
net
wor
k la
yer
prot
ocol
th
at c
an c
arry
IP
info
rmat
ion.
It
is f
airl
y si
mpl
e to
con
figur
e an
d su
ppor
t, b
ut n
ot a
s fu
ll fe
atur
ed a
s O
SPF.
The
fol
low
ing
tabl
e co
mpa
res
crit
ical
par
ts o
f al
l the
rou
ting
pro
toco
ls o
n th
e B
SCI
test
.
EIG
RP
EIG
RP
Ov
erv
iew
EIG
RP
is a
pro
prie
tary
cla
ssle
ss r
outi
ng p
roto
col t
hat
uses
a c
ompl
ex m
etri
c th
at is
ba
sed
on b
andw
idth
and
del
ay. E
IGR
P ad
dres
ses
seve
ral i
ssue
s w
ith IG
RP.
The
follo
win
g ar
e so
me
feat
ures
of
EIG
RP:
•Q
uick
con
verg
ence
.•
Supp
ort
for
VL
SM.
•Is
con
serv
ativ
e of
net
wor
k ba
ndw
idth
.•
Supp
ort
for
IP, A
pple
Talk
, and
IPX
.•
Supp
ort
for
uneq
ual-
cost
pro
port
iona
l loa
d-ba
lanc
ing.
•C
lass
less
.•
Supp
orts
rou
te s
umm
ariz
atio
n by
def
ault
and
auto
mat
ical
ly s
umm
ariz
es a
t cla
ssfu
l ne
twor
k bo
unda
ries
. Man
ual s
umm
ariz
atio
n ca
n al
so b
e do
ne w
ith
EIG
RP.
•U
ses
mul
tica
sts
(and
uni
cast
s w
here
app
ropr
iate
) in
stea
d of
bro
adca
sts.
•E
IGR
P su
ppor
ts a
uthe
ntic
atio
n.
Info
rmati
on
So
urc
eA
D
Ext
erna
l EIG
RP
170
Inte
rnal
BG
P20
0
Unk
now
n25
5
Pro
pert
yR
IPv2
EIG
RP
OS
PF
IS-I
SB
GP
Alg
orit
hmD
ista
nce
Vec
tor
Adv
ance
d D
ista
nce
Vec
tor
Lin
k St
ate
Lin
k St
ate
Path
vec
tor
Pro
pert
yR
IPv2
EIG
RP
OS
PF
IS-I
SB
GP
Sum
mar
izat
ion
Aut
o an
d ar
bitr
ary
Aut
o an
d ar
bitr
ary
Arb
itra
ryA
rbit
rary
Aut
o an
d ar
bitr
ary
VL
SMY
esY
esY
esY
esY
es
Con
verg
eM
inut
esSe
cond
sSe
cond
sSe
cond
sM
inut
es
Tim
ers:
Upd
ate
(hel
lo/d
ead)
Upd
ate
ever
y 30
se
cond
s
Tri
gger
ed,
(LA
N 5
/15,
W
AN
60/
180)
Tri
gger
ed,
LSA
ref
resh
30
min
utes
. (N
BM
A 3
0/12
0, L
AN
10
, 40)
Tri
gger
ed
(10/
30)
Tri
gger
ed
(60/
180)
0910_BSCIssf.fm Page 231 Tuesday, September 9, 2003 8:24 AM
232 BSCI Quick Reference SheetsD
ata
base S
tru
ctu
re
EIG
RP
uses
thr
ee t
able
s:•
The
nei
ghbo
r ta
ble
is b
uilt
fro
m E
IGR
P he
llos
and
used
for
rel
iabl
e de
liver
y.•
The
top
olog
y ta
ble
cont
ains
EIG
RP
rout
ing
info
rmat
ion
for
best
pat
hs a
nd
loop
-fre
e al
tern
ativ
es.
•T
he r
outin
g ta
ble
is u
sed
by E
IGR
P an
d ot
her
rout
ing
prot
ocol
s fo
r al
l bes
t pat
hs.
Ro
ute
Sele
cti
on
An
EIG
RP
rout
er r
ecei
ves
adve
rtis
emen
ts f
rom
eac
h ne
ighb
or t
hat
list
the
adve
rtis
ed
dist
ance
and
fea
sibl
e di
stan
ce t
o a
rout
e. A
dver
tise
d di
stan
ce is
the
met
ric
from
the
ne
ighb
or t
o th
e ne
twor
k. F
easi
ble
dist
ance
is t
he m
etri
c fr
om t
his
rout
er, t
hrou
gh t
he
neig
hbor
, to
the
netw
ork.
The
EIG
RP
path
wit
h th
e lo
wes
t fe
asib
le d
ista
nce
is c
alle
d th
e su
cces
sor
path
. Any
E
IGR
P pa
ths
that
hav
e a
low
er a
dver
tise
d di
stan
ce th
an th
e m
etri
c of
the
succ
esso
r ar
e gu
aran
teed
loop
fre
e an
d ca
lled
feas
ible
suc
cess
ors.
EIG
RP
Metr
icT
he E
IGR
P m
etri
c is
as
follo
ws:
The
k v
alue
s ar
e co
nsta
nts.
The
def
ault
s ar
e k1
= 1
, k2
= 0,
k3
= 1,
k4
= 0,
and
k5
= 0.
If
k5
= 0,
the
fina
l par
t of
the
equ
atio
n (k
5 / [
rel +
k4]
) is
igno
red.
BW
min
is t
he m
inim
um b
andw
idth
alo
ng t
he p
ath—
the
chok
e po
int
band
wid
th.
Del
ay v
alue
s ar
e as
soci
ated
wit
h ea
ch in
terf
ace.
The
sum
of
the
dela
ys (
in 1
0s o
f m
icro
seco
nds)
is u
sed
in t
he e
quat
ion.
Taki
ng t
he c
onst
ants
into
acc
ount
, the
equ
atio
n be
com
es t
his:
If d
efau
lt k
val
ues
are
used
, thi
s w
orks
out
to
be 2
56 (
BW
+ c
umul
ativ
e de
lay)
.B
andw
idth
is th
e la
rges
t con
trib
utor
to th
e m
etri
c. T
he d
elay
val
ue a
llow
s us
to c
hoos
e a
mor
e di
rect
pat
h w
hen
band
wid
th is
equ
ival
ent.
The
EIG
RP
met
ric
is 2
56 t
imes
the
IG
RP
met
ric.
The
tw
o au
tom
atic
ally
red
istr
ibut
e an
d al
gori
thm
ical
ly a
djus
t m
etri
cs if
the
y ar
e co
nfigu
red
on t
he s
ame
rout
er f
or t
he
sam
e au
tono
mou
s sy
stem
.
EIG
RP
Messag
es
Packets
EIG
RP
uses
five
pac
ket
type
s:•
Hel
lo—
Iden
tifie
s ne
ighb
ors
and
serv
es a
s ke
epal
ive
•U
pdat
e—R
elia
bly
send
s ro
ute
info
rmat
ion
•Q
uery
—R
elia
bly
requ
est
spec
ific
rout
e in
form
atio
n•
Rep
ly—
Rel
iabl
e re
spon
se t
o qu
ery
•A
CK
—A
ckno
wle
dgem
ent
EIG
RP
is r
elia
ble,
but
not
all
traf
fic r
equi
res
an A
CK
. Hel
los
are
not
ackn
owle
dged
, an
d th
e ac
know
ledg
emen
t of
a q
uery
is a
rep
ly.
Whe
n E
IGR
P fir
st s
tart
s, it
use
s he
llos
to b
uild
a n
eigh
bor
tabl
e. N
eigh
bors
are
dir
ectl
y at
tach
ed r
oute
rs t
hat
agre
e on
AS
num
ber
and
k va
lues
(ti
mer
s do
n’t
have
to
agre
e).
Subs
eque
nt t
raffi
c is
sen
t w
ith
the
expe
ctat
ion
that
eac
h id
enti
fied
neig
hbor
will
re
spon
d.If
a r
elia
ble
pack
et is
not
ack
now
ledg
ed, E
IGR
P pe
riod
ical
ly r
etra
nsm
its
the
pack
et t
o th
e no
n-re
spon
ding
nei
ghbo
r as
a u
nica
st. E
IGR
P ha
s a
win
dow
siz
e of
one
, so
no
othe
r tr
affic
is s
ent
to t
his
neig
hbor
unt
il it
res
pond
s. A
fter
16
retr
ansm
issi
ons
the
neig
hbor
is r
emov
ed f
rom
the
nei
ghbo
r ta
ble.
Hel
los
also
ser
ve a
s ke
epal
ives
. A n
eigh
bor
is c
onsi
dere
d lo
st if
no
hello
is r
ecei
ved
wit
hin
thre
e he
llo p
erio
ds (
calle
d th
e ho
ld t
ime)
. The
def
ault
tim
ers
are
as f
ollo
ws:
•5
seco
nds/
15 s
econ
ds f
or m
ulti
poin
t ci
rcui
ts w
ith
band
wid
th g
reat
er t
han
T1
and
for
poin
t-to
-poi
nt m
edia
•60
sec
onds
/180
sec
onds
for
oth
er m
ulti
poin
t ci
rcui
ts w
ith
band
wid
th le
ss t
han
or
equa
l to
T1
The
nei
ghbo
r ta
ble
can
be s
een
wit
h th
e co
mm
and
show
ip e
igrp
nei
ghbo
rs.
0910_BSCIssf.fm Page 232 Tuesday, September 9, 2003 8:24 AM
EIGRP DUAL 233
The
pro
cess
of
rout
e ex
chan
ge b
etw
een
two
EIG
RP
rout
ers
is a
s fo
llow
s:1.
Rou
ter
A s
ends
out
a h
ello
.2.
Rou
ter
B se
nds
back
a h
ello
and
an
upda
te. T
he u
pdat
e co
ntai
ns r
outin
g in
form
atio
n.3.
Rou
ter
A a
ckno
wle
dges
the
upd
ate.
4.R
oute
r A
sen
ds it
s up
date
.5.
Rou
ter
B a
ckno
wle
dges
.H
ello
s ar
e us
ed a
s ke
epal
ives
fro
m t
his
poin
t on
. Add
itio
nal r
oute
info
rmat
ion
is s
ent
only
if a
rou
te is
lost
or
new
rou
te d
isco
vere
d.T
he e
xcha
nge
proc
ess
can
be v
iew
ed u
sing
deb
ug ip
eig
rp p
acke
ts, a
nd t
he u
pdat
e pr
oces
s ca
n be
see
n us
ing
debu
g ip
eig
rp.
EIG
RP
DU
AL
Dif
fusin
g U
pd
ate
Alg
ori
thm
(D
UA
L)
DU
AL
is th
e al
gori
thm
use
d by
EIG
RP
to c
hoos
e be
st p
aths
by
look
ing
at a
dver
tised
dis
-ta
nce
(AD
) and
feas
ible
dis
tanc
e (F
D).
Adv
ertis
ed d
ista
nce
is th
e m
etri
c fr
om th
e ne
ighb
or
to th
e de
stin
atio
n. F
easi
ble
dist
ance
is th
e m
etri
c fr
om th
is r
oute
r, th
roug
h th
e ne
ighb
or, t
o th
e de
stin
atio
n. T
he p
ath
with
the
low
est m
etri
c is
cal
led
the
succ
esso
r pa
th. E
IGR
P pa
ths
with
a lo
wer
adv
ertis
ed d
ista
nce
than
the
feas
ible
dis
tanc
e of
the
succ
esso
r pa
th a
re g
uar-
ante
ed lo
op fr
ee a
nd c
alle
d fe
asib
le s
ucce
ssor
s. If
the
succ
esso
r pa
th is
lost
, the
rou
ter
mig
ht
star
t usi
ng th
e fe
asib
le s
ucce
ssor
imm
edia
tely
with
out f
ear
of lo
ops.
Feas
ible
suc
cess
ors
are
not a
lway
s av
aila
ble.
If a
suc
cess
or p
ath
is lo
st a
nd n
o ba
ckup
pat
h is
iden
tified
, the
rou
ter
send
s ou
t que
ries
on
all i
nter
face
s tr
ying
to id
entif
y an
alte
rnat
e pa
th.
Ro
ute
Sele
cti
on
An
easy
way
to u
nder
stan
d th
is is
to c
onsi
der
a dr
ivin
g ex
ampl
e. L
ocat
ed in
Pitt
sbur
gh,
you
are
told
of
thre
e w
ays
to N
ew Y
ork:
•A
dir
ect
path
(43
5 m
iles)
•A
pat
h th
roug
h B
alti
mor
e (A
D: 2
24 m
iles,
FD
: 491
mile
s)•
A p
ath
thro
ugh
Chi
cago
(A
D: 8
51 m
iles,
FD
: 131
9 m
iles)
The
dir
ect
path
wou
ld b
e th
e su
cces
sor
path
; it
has
the
low
est
met
ric.
The
pat
h th
roug
h B
alti
mor
e w
ould
be
a fe
asib
le s
ucce
ssor
—B
alti
mor
e is
clo
ser
to N
ew
Yor
k (2
24 m
iles)
tha
n Pi
ttsb
urgh
(43
5 m
iles)
, so
we’
re s
ure
that
goi
ng t
hrou
gh B
alti
-m
ore
to N
ew Y
ork
does
n’t
invo
lve
loop
ing
back
thr
ough
Pit
tsbu
rgh.
The
pat
h th
roug
h C
hica
go w
ould
not
be
a fe
asib
le s
ucce
ssor
bec
ause
Chi
cago
(85
1 m
iles)
is f
urth
er a
way
fro
m N
ew Y
ork
than
Pit
tsbu
rgh
(435
mile
s) a
nd w
e ca
n’t
say
wit
h ce
rtai
nty
that
tra
velin
g th
roug
h C
hica
go t
o N
ew Y
ork
does
n’t
invo
lve
com
ing
back
thr
ough
Pit
tsbu
rgh.
Netw
ork
Exam
ple
The
fol
low
ing
diag
ram
s sh
ow E
IGR
P ad
vert
isem
ents
fro
m t
he d
esti
nati
on n
etw
ork
to
R3
and
R5.
R5
choo
ses
R4
as th
e su
cces
sor
path
bec
ause
it is
off
erin
g th
e lo
wes
t Fea
sibl
e D
ista
nce.
The
Adv
erti
sed
Dis
tanc
e fr
om R
3 in
dica
tes
that
pas
sing
tra
ffic
thro
ugh
R3
will
not
loop
, so
R3
is a
fea
sibl
e su
cces
sor.
Chi
cago
New
Yor
k
Pitt
sbur
gh
Bal
timor
e
851
Mile
s
458
Mile
s
267
Mile
s
435
Mile
s
224 MilesR
4
R2
R3
R5
R1
All
Link
s H
ave
aD
elay
of 2
0000
µs
FD
: 14,
869,
333
AD
: 14,
357,
333
256
k
192 k
128 k
192
k
576
k15
44 k
FD
: 21,
024,
000
AD
: 2,1
70,0
31
Des
tinat
ion
Net
wor
k
0910_BSCIssf.fm Page 233 Tuesday, September 9, 2003 8:24 AM
234 BSCI Quick Reference Sheets
How
doe
s R
3 ch
oose
its
pat
h? R
1 w
ill
be t
he s
ucce
ssor
, bu
t no
fea
sibl
e su
cces
sor
exis
ts. I
f th
e di
rect
pat
h to
R1
is lo
st t
hen
R3
has
to q
uery
its
neig
hbor
s to
dis
cove
r an
al
tern
ativ
e pa
th. I
t w
aits
to
hear
bac
k fr
om R
2 an
d R
5, b
ut u
ltim
atel
y de
cide
s th
at R
2 is
the
new
suc
cess
or.R
4
R2
R3
R5
R1
All
Link
s H
ave
aD
elay
of 2
0000
µs
256
k
192 k
128 k
192
k
576
k1544 k F
D: 2
,170
,031
AD
: 0
Des
tinat
ion
Net
wor
k
FD
: 13,
845,
333
AD
: 4,9
56,4
44
R4
R2
R3
R5
R1
All
Link
s H
ave
aD
elay
of 2
0000
µs
FD
: 14,
869,
333
AD
: 14,
357,
333
256
k
192 k
128 k
192
k
576
k15
44 k
FD
: 21,
024,
000
AD
: 2,1
70,0
31
Des
tinat
ion
Net
wor
k
0910_BSCIssf.fm Page 234 Tuesday, September 9, 2003 8:24 AM
Advanced EIGRP 235
Co
nfi
gu
rin
g E
IGR
P
Co
nfi
gu
rati
on
EIG
RP
is c
onfig
ured
by
ente
ring
rou
ter
confi
gura
tion
mod
e an
d id
enti
fyin
g th
e cl
assf
ul
netw
orks
wit
hin
whi
ch it
sho
uld
run.
Whe
n se
ttin
g up
EIG
RP,
an
auto
nom
ous
syst
em
num
ber
mus
t be
use
d (7
is u
sed
in t
he e
xam
ple)
. Aut
onom
ous
syst
em n
umbe
rs f
or
EIG
RP
are
not
glob
ally
ass
igne
d, s
o m
ost
inst
alla
tion
s ju
st m
ake
up n
umbe
rs. A
uton
o-m
ous
syst
em n
umbe
rs m
ust
agre
e fo
r tw
o ro
uter
s to
for
m a
nei
ghbo
r re
lati
onsh
ip a
nd
to e
xcha
nge
rout
es.
Router(config)# router eigrp 7
Router(config-router)# network 192.168.1.0
If a
rou
ter
has
two
inte
rfac
es—
e0/0
(19
2.16
8.1.
1/27
) an
d e0
/1 (
192.
168.
1.33
/27)
—an
d ne
eds
to r
un o
nly
EIG
RP
on e
0/0,
the
wild
card
mas
k op
tion
can
be
used
wit
h th
e ne
twor
k co
mm
and:
Router(config-router)# network 192.168.1.0 0.0.0.31
Cre
ati
ng
a D
efa
ult
Ro
ute
You
can
pro
duce
a d
efau
lt r
oute
in E
IGR
P in
thr
ee w
ays:
•R
1 ca
n sp
ecif
y a
defa
ult
netw
ork:
R1(config)# ip default-network 10.0.0.0
R3
now
see
s a
defa
ult
netw
ork
wit
h a
next
hop
of
R1.
•Pr
oduc
e a
sum
mar
y ro
ute:
R1(config)# interface s0
R1(config-if)# ip summary-address eigrp 7 0.0.0.0 0.0.0.0
Thi
s pa
sses
a d
efau
lt r
oute
fro
m R
1 ou
t it
s se
rial
0 in
terf
ace
tow
ard
R3.
•C
reat
e a
stat
ic d
efau
lt r
oute
and
the
n in
clud
e ne
twor
k 0.
0.0.
0 in
EIG
RP:
R1(config)# ip route 0.0.0.0 0.0.0.0 10.1.1.2
R1(config)# router eigrp 7
R1(config-router)# network 0.0.0.0
Tro
ub
lesh
oo
tin
g E
IGR
PT
he m
ost
stra
ight
forw
ard
way
to
trou
bles
hoot
EIG
RP
is t
o in
spec
t th
e ro
utin
g ta
ble—
show
ip r
oute
. To
filte
r th
e ro
utin
g ta
ble
and
show
onl
y th
e ro
utes
lear
ned
from
E
IGR
P us
e sh
ow ip
rou
te e
igrp
.sh
ow ip
pro
toco
ls is
alw
ays
the
first
pla
ce t
o ch
eck
whe
n in
vest
igat
ing
rout
ing
prot
ocol
is
sues
. Use
this
com
man
d to
ver
ify a
uton
omou
s sy
stem
, tim
er v
alue
s, id
entifi
ed n
etw
orks
, an
d E
IGR
P ne
ighb
ors
(rou
ting
info
rmat
ion
sour
ces)
.E
IGR
P sp
ecifi
c is
sues
can
be
inve
stig
ated
usi
ng s
how
ip e
igrp
topo
logy
. Thi
s sh
ows
the
EIG
RP
topo
logy
tab
le a
nd id
enti
fies
succ
esso
rs a
nd f
easi
ble
succ
esso
rs.
Ad
van
ced
EIG
RP
Su
mm
ari
zati
on
Just
like
RIP
v2, E
IGR
P de
faul
ts t
o au
tom
atic
ally
sum
mar
izin
g at
cla
ssfu
l net
wor
k bo
unda
ries
. Thi
s is
com
mon
ly d
isab
led
and
arbi
trar
y su
mm
ariz
atio
n is
em
ploy
ed.
Router(config-router)# no auto-summary
Sum
mar
ies
can
be p
rodu
ced
man
ually
on
any
inte
rfac
e. W
hen
a su
mm
ary
is p
rodu
ced,
a
mat
chin
g ro
ute
to n
ull0
als
o be
com
es a
ctiv
e as
a lo
op p
reve
ntio
n m
echa
nism
. Con
-fig
ure
a su
mm
ary
rout
e ou
t a
part
icul
ar in
terf
ace
usin
g th
e ip
sum
mar
y-ad
dres
s ei
grp
AS
com
man
d. T
he f
ollo
win
g ex
ampl
e us
es E
IGR
P A
S 7
and
adve
rtis
es a
def
ault
rou
te
out
ethe
rnet
0 an
d a
sum
mar
y ro
ute
172.
16.1
04.0
/22
out
seri
al0.
Router(config)# int e0
Router(config-if)# ip summary-address eigrp 7 0.0.0.0 0.0.0.0
Router(config)# int s0
Router(config-if)# ip summary-address eigrp 7 172.16.104.0 255.255.252.0
Lo
ad
Bala
ncin
gE
IGR
P, li
ke m
ost I
P ro
utin
g pr
otoc
ols
on a
Cis
co r
oute
r, au
tom
atic
ally
load
bal
ance
s ov
er
equa
l cos
t pa
ths.
Wha
t m
akes
EIG
RP
uniq
ue is
tha
t it
pro
port
iona
lly lo
ad b
alan
ces
R3
R1
Inte
rnet
10.1
.1.0
/30
192.
168.
224/
30
192.
168.
1.0/
2719
2.16
8.1.
64/2
7
0910_BSCIssf.fm Page 235 Tuesday, September 9, 2003 8:24 AM
236 BSCI Quick Reference Sheetsov
er u
nequ
al c
ost p
aths
. A v
aria
nce
is s
peci
fied
and
load
bal
anci
ng is
use
d fo
r an
y pa
th
wit
h a
met
ric
of le
ss t
han
the
prod
uct
of t
he v
aria
nce
and
the
best
met
ric.
In t
his
exam
ple,
R5
uses
the
pat
h th
roug
h R
4 si
nce
it o
ffer
s th
e lo
wes
t m
etri
c (1
4,86
9,33
3). T
o se
t up
une
qual
cos
t lo
ad b
alan
cing
, ass
ign
a va
rian
ce o
f 2,
and
now
R
5 us
es a
ll pa
ths
with
a m
etri
c le
ss th
an 2
9,73
8,66
6. T
his
incl
udes
the
path
thro
ugh
R3.
R5(config-router)# variance 2
WA
N B
an
dw
idth
Oth
er r
outi
ng p
roto
cols
bur
st to
use
all
avai
labl
e lin
k ba
ndw
idth
. Bec
ause
rou
ting
pro
-to
col t
raffi
c is
tre
ated
as
havi
ng a
hig
her
prio
rity
, thi
s ca
n so
met
imes
lock
out
dat
a tr
affic
ove
r W
AN
link
s. E
IGR
P is
uni
que
in o
ffer
ing
a w
ay t
o co
ntro
l thi
s. B
y de
faul
t,
EIG
RP
limit
s it
self
to
burs
ting
to
half
the
link
ban
dwid
th. T
his
limit
is c
onfig
urab
le
usin
g th
e ip
ban
dwid
th-p
erce
nt c
omm
and.
The
fol
low
ing
exam
ple
assu
mes
EIG
RP
AS
7 an
d lim
its
EIG
RP
to a
fou
rth
of li
nk b
andw
idth
:Router(config-if)# ip bandwidth-percent eigrp 7 25
The
def
ault
val
ue is
acc
epta
ble
in m
ost c
ases
. The
rea
l iss
ue w
ith
WA
N li
nks
is th
at th
e ro
uter
ass
umes
tha
t ea
ch li
nk h
as 1
544
kbps
ban
dwid
th. I
f se
rial
0 is
att
ache
d to
a 1
28
k fr
acti
onal
T1,
EIG
RP
assu
mes
it c
an b
urst
to
768
k an
d co
uld
over
whe
lm t
he li
ne.
Thi
s is
rec
tifie
d by
cor
rect
ly id
enti
fyin
g lin
k ba
ndw
idth
.Router (config)# int serial 0
Router (config-if)# bandwidth 128
One
situ
atio
n su
gges
ts it
self
whe
re a
ll th
ese
tech
niqu
es c
an b
e co
mbi
ned—
Fram
e R
elay
.
In t
his
confi
gura
tion
, R1
has
a 25
6 K
con
nect
ion
to t
he F
ram
e R
elay
net
wor
k an
d tw
o pe
rman
ent
virt
ual c
ircu
its
(PV
Cs)
wit
h co
mm
itte
d in
form
atio
n ra
tes
(CIR
) (m
inim
um
guar
ante
ed b
andw
idth
) of
128
K a
nd 6
4 K
. Wha
t va
lue
shou
ld b
e us
ed f
or t
he in
ter-
face
ban
dwid
th in
thi
s ca
se?
The
usu
al s
ugge
stio
n is
to
use
the
CIR
, but
the
tw
o PV
Cs
have
dif
fere
nt C
IRs.
Spe
cify
ing
a ba
ndw
idth
of 1
28 o
n th
e m
ain
inte
rfac
e le
ads
EIG
RP
to a
ssum
e a
band
wid
th o
f 64
for
eac
h PV
C, b
ut c
ause
s th
e ro
uter
to
inco
rrec
tly
repo
rt
utili
zati
on t
hrou
gh S
impl
e N
etw
ork
Man
agem
ent
Prot
ocol
(SN
MP)
. We
coul
d us
e th
e ba
ndw
idth
-per
cent
com
man
d to
allo
w a
tru
e ba
ndw
idth
val
ue w
hile
adj
usti
ng t
he
burs
t ra
te t
o 64
k f
or e
ach
PVC
.R1(config)# int serial 0
R1 (config-if)# bandwidth 256
R1 (config-if)# ip bandwidth-percent eigrp 7 25
R4
R2
R3
R5
R1
All
Link
s H
ave
aD
elay
of 2
0000
us
FD
: 14,
869,
333
AD
: 14,
357,
333
256
k
192 k
128 k
192
k
576
k15
44 k
FD
: 21,
024,
000
AD
: 2,1
70,0
31
Des
tinat
ion
Net
wor
k
R3
R1
R2
Fram
e R
elay
Net
wor
k
PV
C12
8 K
CIR
PV
C64
K C
IR
256 K
0910_BSCIssf.fm Page 236 Tuesday, September 9, 2003 8:24 AM
OSPF Overview 237
A b
ette
r so
luti
on is
to u
se s
ubin
terf
aces
and
iden
tify
ban
dwid
th s
epar
atel
y. In
this
cas
e,
s0.1
bur
sts
to 6
4 k,
and
s0.
2 bu
rsts
to
32 k
.R1(config)#int serial 0.1
R1 (config-if)# bandwidth 128
R1(config)# int serial 0.2
R1 (config-if)# bandwidth 10
R1 (config-if)# ip bandwidth-percent eigrp 7 320
Not
ice
that
an
arbi
trar
ily lo
w v
alue
has
bee
n us
ed f
or t
he s
econ
d PV
C.
OS
PF O
verv
iew
Dijkstr
a A
lgo
rith
mO
SPF
is a
n op
en s
tand
ard
clas
sles
s ro
utin
g pr
otoc
ol th
at c
onve
rges
qui
ckly
and
use
s co
st
as a
met
ric
(cos
t is
by d
efau
lt au
tom
atic
ally
ass
ocia
ted
with
ban
dwid
th b
y C
isco
IOS)
.O
SPF
is a
link
-sta
te r
outi
ng p
roto
col a
nd u
ses
Dijk
stra
’s Sh
orte
st P
ath
Firs
t (S
PF)
algo
rith
m t
o de
term
ine
best
pat
hs. T
he fi
rst
resp
onsi
bilit
y of
a li
nk-s
tate
rou
ter
is t
o cr
eate
a d
atab
ase
that
refl
ects
the
str
uctu
re o
f th
e ne
twor
k.T
he r
oute
r ex
chan
ges
hello
s w
ith
each
nei
ghbo
r, le
arni
ng R
oute
r ID
(R
ID)
and
cost
.T
he r
oute
r th
en c
onst
ruct
s a
Lin
k St
ate
Adv
erti
sem
ent (
LSA
) wit
h th
e R
IDs
and
cost
to
each
nei
ghbo
r.E
ach
rout
er in
the
rou
ting
dom
ain
shar
es it
s L
SA w
ith
all o
ther
rou
ters
. Eac
h ro
uter
ke
eps
the
com
plet
e se
t of
LSA
s in
a t
able
—th
e L
ink
Stat
e D
atab
ase.
Eac
h ro
uter
run
s th
e SP
F al
gori
thm
to
com
pute
bes
t pa
ths.
Descri
pti
on
of
the S
PF A
lgo
rith
mT
he f
ollo
win
g se
ctio
n is
hel
pful
for
und
erst
andi
ng t
he o
pera
tion
of
the
SPF
algo
rith
m,
but
it is
not
tes
ted
in t
his
dept
h on
the
BSC
I ex
am. T
he S
PF a
lgor
ithm
use
s fo
ur t
able
s:•
Lin
k St
ate
Dat
abas
e—A
ll L
SAs
•T
enta
tive
—A
scr
atch
pad
tab
le f
or t
he a
lgor
ithm
•Pa
th—
The
bes
t O
SPF
path
•R
outi
ng T
able
—T
he b
est
path
giv
en a
ll so
urce
sT
he S
PF a
lgor
ithm
ope
rate
s on
eac
h ro
uter
in fi
ve s
teps
:St
ep 1
Plac
e m
ysel
f in
pat
h ta
ble
wit
h a
cost
of
zero
.
Step
2Fo
r th
e ne
w e
ntry
in t
he p
ath
tabl
e, lo
ok a
t it
s L
SA in
the
Lin
k St
ate
Dat
a-ba
se. A
dd t
he p
ath
cost
to
the
node
to
the
LSA
cos
t. F
or e
ach
neig
hbor
, if
not
alre
ady
in t
he p
ath
or t
enta
tive
tab
le w
ith
a be
tter
cos
t, p
lace
in t
he
tent
ativ
e ta
ble.
Step
3If
the
ten
tati
ve t
able
is e
mpt
y, s
top.
Step
4Fi
nd t
he lo
wes
t co
st e
ntry
in t
he t
enta
tive
tab
le a
nd m
ove
to it
to
the
path
ta
ble.
Step
5G
o to
Ste
p 2.
For
exam
ple,
con
side
r th
e fo
llow
ing
netw
ork.
Rou
ter
B b
uild
s an
LSA
tha
t sa
ys, “
My
nam
e is
B, a
nd I
hav
e a
neig
hbor
A w
ith
a co
st
of 1
, nei
ghbo
r C
wit
h a
cost
of
2, a
nd n
eigh
bor
E w
ith
a co
st o
f 2.
”T
he L
SAs
are
dist
ribu
ted,
and
the
Dijk
stra
alg
orit
hm is
run
.R
oute
r B
sta
rts
by p
laci
ng it
self
at
the
root
of
the
netw
ork
wit
h a
cost
of
zero
. B’s
LSA
is
add
ed t
o th
e te
nt.
The
low
est c
ost e
ntry
in te
nt is
A, s
o it
is m
oved
to th
e pa
th a
nd it
s L
SA is
inco
rpor
ated
in
the
tent
ativ
e da
taba
se. B
ecau
se B
is a
lrea
dy in
the
pat
h, a
n en
try
for
B (
via
A)
is n
ot
adde
d to
the
ten
tati
ve d
atab
ase.
To
po
log
yP
ath
Te
nt
BB
cos
t 0
A c
ost
1C
cos
t 2
E c
ost
2
To
po
log
yP
ath
Te
nt
B | A
B c
ost
0A
cos
t 1
C c
ost
2D
via
A c
ost
1 +
3 =
4E
cos
t 2
C
BA D
E
1
2
2
3
7
5
0910_BSCIssf.fm Page 237 Tuesday, September 9, 2003 8:24 AM
238 BSCI Quick Reference SheetsT
he lo
wes
t cos
t ent
ry in
tent
is n
ow C
or
E. C
hoos
ing
C, i
t is
mov
ed to
the
path
and
its
LSA
is in
corp
orat
ed in
the
ten
tati
ve d
atab
ase.
Bec
ause
E is
alr
eady
in t
he t
enta
tive
da
taba
se w
ith a
low
er c
ost,
the
entr
y fo
r E
(via
C) i
s no
t add
ed to
the
tent
ativ
e da
taba
se.
The
low
est c
ost e
ntry
in te
nt is
now
E. I
t is
mov
ed to
the
path
and
its
LSA
is in
corp
orat
ed
in t
he t
enta
tive
dat
abas
e. B
ecau
se D
is a
lrea
dy in
the
ten
tati
ve d
atab
ase
wit
h a
low
er
cost
, the
ent
ry f
or D
(vi
a E
) is
not
add
ed t
o th
e te
ntat
ive
data
base
.
The
low
est c
ost e
ntry
in te
nt is
now
D. I
t is
mov
ed to
the
path
and
its
LSA
is in
corp
orat
ed
in t
he t
enta
tive
dat
abas
e. B
ecau
se E
and
A a
re a
lrea
dy in
the
pat
h da
taba
se w
ith
a lo
wer
cos
t, t
he t
enta
tive
dat
abas
e is
now
em
pty.
The
alg
orit
hm is
now
com
plet
e, a
nd t
he b
est
path
s fr
om B
to
any
othe
r lo
cati
on a
re
now
inco
rpor
ated
fro
m t
he p
ath
data
base
into
the
rou
ting
tab
le.
Netw
ork
Str
uctu
reO
SPF
rout
ing
dom
ains
are
bro
ken
up in
to a
reas
. The
SPF
alg
orit
hm r
uns
wit
hin
an
area
, and
inte
r-ar
ea r
oute
s ar
e pa
ssed
bet
wee
n ar
eas.
A t
wo-
leve
l hie
rarc
hy t
o O
SPF
area
s ex
ists
—ot
her
area
s ar
e al
way
s at
tach
ed d
irec
tly
to a
rea
0 an
d on
ly t
o ar
ea 0
.
OSP
F ar
eas
do t
he f
ollo
win
g:•
Min
imiz
e th
e nu
mbe
r of
rou
ting
tab
le e
ntri
es a
nd t
he n
umbe
r of
tim
es t
he S
PF
algo
rith
m is
run
.•
Con
tain
LSA
floo
ding
to
a re
ason
able
are
a.•
Are
rec
omm
ende
d to
con
tain
50–
100
rout
ers.
Rou
ter
role
s ar
e de
fined
as
wel
l.A
n in
tern
al r
oute
r ha
s al
l int
erfa
ces
in o
ne a
rea
(R5,
R2,
R1)
.A
n A
rea
Bor
der
Rou
ter
(AB
R)
has
inte
rfac
es in
tw
o or
mor
e ar
eas
(R3,
R4)
.A
n A
uton
omou
s Sy
stem
Bou
ndar
y R
oute
r (A
SBR
) ha
s in
terf
aces
insi
de a
nd o
utsi
de
the
OSP
F ro
utin
g do
mai
n.
LS
A U
pd
ate
Eac
h ro
uter
mai
ntai
ns a
dat
abas
e of
the
late
st r
ecei
ved
LSA
s. E
ach
LSA
is n
umbe
red
wit
h a
sequ
ence
num
ber,
and
a ti
mer
is r
un t
o ag
e ou
t ol
d L
SAs.
Whe
n a
LSA
is r
ecei
ved,
it’s
com
pare
d to
the
LS
data
base
. If
it is
new
the
n it
is a
dded
to
the
data
base
and
the
SPF
algo
rith
m is
run
. If i
t is
from
a R
oute
r ID
that
is a
lrea
dy in
th
e da
taba
se, t
hen
the
sequ
ence
num
ber
is c
ompa
red,
and
old
er L
SAs
are
disc
arde
d. I
f it
is a
new
LSA
, it
is in
corp
orat
ed in
the
dat
abas
e, a
nd t
he S
PF a
lgor
ithm
is r
un. I
f it
is
an o
lder
LSA
, the
new
er L
SA in
mem
ory
is s
ent
back
to
who
ever
sen
t th
e ol
d on
e.
To
po
log
yP
ath
Ten
t
B / \ A
C
B c
ost
0A
cos
t 1
C c
ost
2
D v
ia A
cos
t 1
+ 3
= 4
E c
ost
2
To
po
log
yP
ath
Ten
t
B / \
\A
C
E
B c
ost
0A
cos
t 1
C c
ost
2E
cos
t 2
D v
ia A
cos
t 1
+ 3
= 4
To
po
log
yP
ath
Ten
t
B / \
\A
C
E
|
D
B c
ost
0A
cos
t 1
C c
ost
2E
cos
t 2
D c
ost
4
R3
R2
R4
R1
R5
Are
a 0
Are
a 1
Are
a 2
0910_BSCIssf.fm Page 238 Tuesday, September 9, 2003 8:24 AM
Low-Level OSPF 239
Co
nfi
gu
rin
g S
ing
le A
rea O
SP
F
Co
nfi
gu
rati
on
OSP
F is
con
figur
ed b
y en
teri
ng r
oute
r co
nfigu
rati
on m
ode
and
iden
tify
ing
the
rang
e of
in
terf
ace
addr
esse
s on
whi
ch it
sho
uld
run
and
the
area
s th
ey a
re in
. Whe
n se
ttin
g up
O
SPF,
a p
roce
ss I
D m
ust
be u
sed
(8 is
use
d in
the
exa
mpl
e), b
ut t
he p
roce
ss I
D d
oes
not
have
to
agre
e on
dif
fere
nt O
SPF
devi
ces
for
them
to
exch
ange
info
rmat
ion.
The
ne
twor
k st
atem
ent
uses
a w
ildca
rd m
ask
and
can
spec
ify
any
rang
e fr
om a
sin
gle
addr
ess
to a
ll ad
dres
ses.
Router(config)# router ospf 8
Router(config-router)# network 192.168.1.0 0.0.0.255 area 0
Tro
ub
lesh
oo
tin
g O
SP
FT
he fi
rst
plac
e O
SPF
issu
es a
re n
otic
ed is
whe
n in
spec
ting
the
rou
ting
tab
le—
show
ip
rout
e. T
o fil
ter
the
rout
ing
tabl
e an
d on
ly s
how
the
rou
tes
lear
ned
from
OSP
F us
e sh
ow ip
rou
te o
spf.
show
ip p
roto
cols
sho
uld
be u
sed
next
. It o
ffer
s a
wea
lth
of in
form
atio
n fo
r an
y ro
utin
g pr
otoc
ol is
sue.
Use
this
com
man
d to
ver
ify
para
met
ers,
tim
er v
alue
s, id
enti
fied
netw
orks
, an
d O
SPF
neig
hbor
s (“
rout
ing
info
rmat
ion
sour
ces”
).B
ecau
se w
ildca
rd m
asks
som
etim
es in
corr
ectl
y gr
oup
inte
rfac
es to
are
as, a
noth
er g
ood
plac
e to
che
ck is
sho
w ip
osp
f in
terf
aces
. Thi
s sh
ows
the
inte
rfac
es o
n w
hich
OSP
F is
ru
nnin
g an
d th
eir
curr
ent
corr
ect
assi
gned
are
a.sh
ow ip
osp
f sh
ows
the
RID
, tim
ers,
and
cou
nter
s. s
how
ip o
spf
neig
hbor
s sh
ows
the
OSP
F ne
ighb
or ta
ble,
iden
tifie
s ad
jace
ncy
stat
us, a
nd r
evea
ls th
e de
sign
ated
rou
ter
and
back
up d
esig
nate
d ro
uter
.
Ro
ute
r ID
The
SPF
alg
orit
hm is
use
d to
map
the
sho
rtes
t pa
th b
etw
een
a se
ries
of
node
s. T
he
issu
e is
tha
t an
IP
rout
er is
not
iden
tifie
d by
a s
ingl
e nu
mbe
r—it
s in
terf
aces
are
. For
re
ason
s of
com
pati
bilit
y w
ith
the
prot
ocol
a s
ingl
e ad
dres
s is
use
d as
the
“na
me”
of
the
rout
er—
the
Rou
ter
ID (
RID
).B
y de
faul
t, t
he R
oute
r ID
is t
he h
ighe
st lo
opba
ck I
P ad
dres
s. I
f no
loop
back
add
ress
es
are
confi
gure
d, t
he R
ID is
the
hig
hest
IP
addr
ess
on a
n ac
tive
inte
rfac
e w
hen
the
OSP
F pr
oces
s is
sta
rted
. The
rou
ter
ID is
sel
ecte
d w
hen
OSP
F st
arts
and
—fo
r re
ason
s of
sta
-bi
lity—
is n
ot c
hang
ed u
ntil
OSP
F re
star
ts. O
f co
urse
, the
OSP
F pr
oces
s ca
n be
re
star
ted
by r
eboo
ting
or
by u
sing
the
com
man
d cl
ear
ip o
spf
proc
ess.
Eit
her
choi
ce
affe
cts
rout
ing
in y
our
netw
ork
for
a pe
riod
of t
ime
and
shou
ld b
e us
ed o
nly
with
cau
tion.
A lo
opba
ck in
terf
ace
is a
vir
tual
inte
rfac
e. A
loop
back
add
ress
is c
onfig
ured
by
crea
ting
an
inte
rfac
e an
d as
sign
ing
an I
P ad
dres
s.Router(config)# interface loopback0
Router(config-if)# ip address 10.0.0.1 255.255.255.255
The
loop
back
add
ress
doe
s no
t ha
ve t
o be
incl
uded
in t
he O
SPF
rout
ing
proc
ess,
but
it
ofte
n is
to
prov
ide
a lo
cati
on t
o pi
ng o
r tr
ace
to.
A w
ay to
sho
rt-c
ircu
it th
e R
ID s
elec
tion
is to
ass
ign
it us
ing
the
OSP
F ro
uter
-id c
omm
and.
Router(config)# router ospf 8
Router(config-router)# router-id 10.0.0.1
Lo
w-L
evel O
SP
F
Packets
OSP
F us
es fi
ve p
acke
t ty
pes:
•H
ello
—Id
enti
fies
neig
hbor
s an
d se
rves
as
keep
aliv
e.•
Lin
k St
ate
Req
uest
(L
SR)—
A r
eque
st f
or a
n L
SU. C
onta
ins
the
type
of
LSU
re
ques
ted
and
the
ID o
f th
e ro
uter
req
uest
ing
it.
•D
atab
ase
Des
crip
tion
(D
BD
)—A
sum
mar
y of
the
Lin
k St
ate
Dat
abas
e, in
clud
ing
the
RID
and
seq
uenc
e nu
mbe
r of
eac
h L
SA in
the
Lin
k St
ate
Dat
abas
e.•
Lin
k St
ate
Upd
ate
(LSU
)—C
onta
ins
a fu
ll L
SA (
link
stat
e ad
vert
isem
ent)
ent
ry.
An
LSA
incl
udes
top
olog
y in
form
atio
n, f
or e
xam
ple
the
RID
of
this
rou
ter
and
the
RID
and
cos
t to
eac
h ne
ighb
or. O
ne L
SU c
an c
onta
in m
ulti
ple
LSA
s.•
Lin
k St
ate
Ack
now
ledg
men
t (L
SAck
)—A
ckno
wle
dges
all
othe
r O
SPF
pack
ets
(exc
ept
hello
s).
All
five
pack
et t
ypes
are
dir
ectl
y pl
aced
into
an
IP p
acke
t (I
P pr
otoc
ol 8
9) u
sing
a
com
mon
OSP
F he
ader
.
Neig
hb
ors
hip
OSP
F ro
uter
s se
nd o
ut p
erio
dic
mul
tica
st p
acke
ts t
o in
trod
uce
them
selv
es t
o ot
her
rout
ers
on a
link
. The
y be
com
e ne
ighb
ors
whe
n th
ey h
ear
thei
r ow
n ro
uter
ID in
clud
ed
in t
he h
ello
of
anot
her
rout
er, t
hus
prov
ing
bidi
rect
iona
l com
mun
icat
ion.
OSP
F tr
affic
is m
ulti
cast
to
eith
er o
f tw
o ad
dres
ses:
224.
0.0.
5—A
ll SP
F R
oute
rs22
4.0.
0.6—
All
SPF
DR
s
0910_BSCIssf.fm Page 239 Tuesday, September 9, 2003 8:24 AM
240 BSCI Quick Reference SheetsO
SPF
rout
ers,
if c
erta
in p
aram
eter
s ag
ree,
bec
ome
neig
hbor
s w
hen
they
see
them
selv
es
in t
he “
neig
hbor
s” fi
eld
of a
n in
com
ing
hello
. The
fol
low
ing
mus
t m
atch
:•
Tim
er v
alue
s•
Are
a ID
•Pa
ssw
ord
(if
used
)•
Com
mon
sub
net
•St
ub a
rea
flag
(T/F
)O
SPF
rout
ers
can
be n
eigh
bors
wit
hout
bei
ng a
djac
ent.
Onl
y ad
jace
nt n
eigh
bors
ex
chan
ge r
outi
ng u
pdat
es a
nd s
ynch
roni
ze t
heir
dat
abas
es. O
n a
poin
t-to
-poi
nt li
nk,
an a
djac
ency
is e
stab
lishe
d be
twee
n th
e tw
o ro
uter
s w
hen
they
can
com
mun
icat
e. O
n a
mul
tiac
cess
link
, eac
h ro
uter
est
ablis
hes
an a
djac
ency
onl
y w
ith
the
DR
and
the
ba
ckup
DR
(B
DR
).H
ello
s al
so s
erve
as
keep
aliv
es. A
nei
ghbo
r is
con
side
red
lost
if n
o H
ello
is r
ecei
ved
wit
hin
four
Hel
lo p
erio
ds (
calle
d th
e de
ad t
ime)
. The
def
ault
tim
ers
are
as f
ollo
ws:
•10
sec
onds
/40
seco
nds
for
LA
N a
nd p
oint
-to-
poin
t in
terf
aces
•30
sec
onds
/120
sec
onds
for
non
broa
dcas
t m
ulti
acce
ss (
NB
MA
) in
terf
aces
The
nei
ghbo
r ta
ble
can
be s
een
wit
h sh
ow ip
osp
f ne
ighb
ors.
The
pro
cess
of
rout
e ex
chan
ge b
etw
een
two
OSP
F ro
uter
s is
as
follo
ws:
1.D
own
stat
e: R
oute
r A
sen
ds a
hel
lo t
hat
lists
no
neig
hbor
s.2.
Init
sta
te: R
oute
r B
sen
ds a
hel
lo t
hat
lists
A a
s a
neig
hbor
.Tw
o-w
ay s
tate
: Rou
ter
A s
ees
Rou
ter
B’s
hello
and
add
s it
to th
e ne
ighb
or d
atab
ase.
(I
f one
rou
ter
is n
ot D
R o
r B
DR
and
this
is a
mul
tiacc
ess
link,
pro
cess
sto
ps h
ere.
)
3.E
xsta
rt s
tate
: One
rou
ter
asse
rts
itse
lf a
s th
e le
ad in
exc
hang
ing
rout
es.
4.E
xcha
nge
stat
e: T
he le
ad r
oute
r se
nds
its
DB
D li
stin
g th
e L
SAs
in it
s L
S da
taba
se
by R
ID a
nd s
eque
nce
num
ber.
5.T
he o
ther
rou
ter
repl
ies
wit
h it
s D
BD
.6.
Eac
h ro
uter
sen
ds a
n L
SAck
.7.
Loa
ding
sta
te: E
ach
rout
er c
ompa
res
the
DB
D r
ecei
ved
to th
e co
nten
ts o
f its
Lin
k St
ate
data
base
. It
then
sen
ds a
Lin
k St
ate
Req
uest
ask
ing
for
mis
sing
or
outd
ated
L
SAs.
8.T
he n
eigh
bor
repl
ies
to t
he r
eque
st.
9.T
he r
oute
r ac
know
ledg
es r
ecei
pt.
10.
Full
stat
e: L
ink
Stat
e D
atab
ases
are
syn
chro
nize
d.
Seq
uen
ce N
um
bers
OSP
F se
quen
ce n
umbe
rs a
re 3
2 bi
ts. T
he fi
rst
lega
l seq
uenc
e nu
mbe
r is
0x8
0000
001.
L
arge
r nu
mbe
rs a
re m
ore
rece
nt.
Nor
mal
ly, t
he s
eque
nce
num
ber
chan
ges
only
und
er t
wo
cond
itio
ns:
•T
he L
SA c
hang
es b
ecau
se a
rou
te is
add
ed o
r de
lete
d.•
The
LSA
age
s ou
t (L
SAs
are
upda
ted
ever
y ha
lf h
our,
even
if n
othi
ng c
hang
es).
The
com
man
d sh
ow ip
osp
f dat
abas
e sh
ows
the
age
(in
seco
nds)
and
seq
uenc
e nu
mbe
r fo
r ea
ch R
ID.
Tro
ub
lesh
oo
tin
gT
he n
eigh
bor
init
ializ
atio
n pr
oces
s ca
n be
vie
wed
usi
ng d
ebug
ip o
spf
adja
cenc
ies.
A
ll O
SPF
traf
fic c
an b
e se
en f
rom
deb
ug ip
osp
f pa
cket
.
OS
PF N
etw
ork
Typ
es
Exp
ecta
tio
ns o
f D
ijkstr
a’s
SP
F A
lgo
rith
mT
he S
PF a
lgor
ithm
bui
lds
a di
rect
ed g
raph
—pa
ths
mad
e up
of
a se
ries
of
poin
ts c
on-
nect
ed b
y di
rect
link
s. O
ne o
f th
e co
nseq
uenc
es o
f th
is “
dire
cted
gra
ph”
appr
oach
is
that
the
algo
rith
m h
as n
o w
ay to
han
dle
a m
ulti
acce
ss n
etw
ork.
The
sol
utio
n us
ed is
to
elec
t on
e ro
uter
to
repr
esen
t th
e en
tire
seg
men
t—a
desi
gnat
ed r
oute
r (D
R).
Desig
nate
d R
ou
ters
Poin
t-to
-poi
nt li
nks
fit t
he S
PF m
odel
per
fect
ly a
nd d
on’t
need
any
spe
cial
mod
elin
g m
etho
d. O
n a
poin
t-to
-poi
nt li
nk, n
o D
R is
ele
cted
and
all
traf
fic is
mul
tica
st t
o 22
4.0.
0.5.
On
a m
ulti
acce
ss li
nk o
ne o
f th
e ro
uter
s is
ele
cted
as
a de
sign
ated
rou
ter
(DR
) an
d an
othe
r as
a b
acku
p D
R (
BD
R).
All
othe
r ro
uter
s on
tha
t lin
k be
com
e ad
jace
nt o
nly
to t
he D
R a
nd B
DR
, not
to
each
oth
er (
they
sto
p at
the
two-
way
sta
te).
The
DR
is
resp
onsi
ble
for
crea
ting
and
flood
ing
a ne
twor
k L
SA (t
ype
2) a
dver
tisin
g th
e m
ultia
cces
s lin
k. N
on-D
R (D
RO
TH
ER
) rou
ters
com
mun
icat
e w
ith th
e D
Rs
usin
g IP
add
ress
22
4.0.
0.6.
The
DR
s us
e IP
add
ress
224
.0.0
.5 to
pas
s in
form
atio
n to
oth
er r
oute
rs.
The
DR
and
BD
R a
re e
lect
ed a
s fo
llow
s:•
A s
tart
ing
rout
er li
sten
s fo
r O
SPF
hello
s. If
non
e ar
e he
ard
wit
hin
the
dead
tim
e, it
de
clar
es it
self
the
DR
.•
If o
ne o
r m
ore
othe
r ro
uter
s ar
e he
ard,
the
rou
ter
wit
h th
e hi
ghes
t O
SPF
prio
rity
is
ele
cted
DR
, and
the
ele
ctio
n pr
oces
s st
arts
aga
in f
or B
DR
. Pri
orit
y of
zer
o re
mov
es a
rou
ter
from
the
ele
ctio
n.•
If t
wo
or m
ore
rout
ers
have
the
sam
e O
SPF
prio
rity
, the
rou
ter
wit
h th
e hi
ghes
t R
ID is
ele
cted
DR
, and
the
ele
ctio
n pr
oces
s st
arts
aga
in f
or B
DR
.
0910_BSCIssf.fm Page 240 Tuesday, September 9, 2003 8:24 AM
OSPF Network Types 241
•D
R e
lect
ion
does
not
tak
e pl
ace
agai
n un
less
the
DR
or
BD
R a
re lo
st. B
ecau
se o
f th
is, t
he D
R is
som
etim
es t
he fi
rst
devi
ce s
tart
ed w
ith
a no
n-ze
ro p
rior
ity.
As
men
tion
ed, t
he b
est w
ay to
spe
cify
a r
oute
r to
be
the
DR
is to
use
the
OSP
F pr
iori
ty.
The
def
ault
pri
orit
y is
one
. A p
rior
ity
of z
ero
mea
ns t
hat
a ro
uter
doe
s no
t ac
t as
DR
or
BD
R—
it c
an b
e on
ly a
DR
OT
HE
R. P
rior
ity
can
be s
et w
ith
the
ip o
spf
prio
rity
co
mm
and
in in
terf
ace
confi
gura
tion
mod
e.Router(config)# int ethernet 0
Router(config-if)# ip ospf priority 2
No
nb
road
cast
Mu
ltia
ccess N
etw
ork
sR
outi
ng p
roto
cols
ass
ume
that
mul
tiac
cess
link
s su
ppor
t br
oadc
ast
and
have
ful
l co
nnec
tivity
(fro
m a
ny d
evic
e to
any
dev
ice)
. In
term
s of
OSP
F, th
is m
eans
the
follo
win
g:•
All
Fram
e R
elay
or
AT
M m
aps
shou
ld in
clud
e th
e br
oadc
ast
attr
ibut
e.•
DR
and
BD
R s
houl
d ha
ve f
ull V
C c
onne
ctiv
ity
to a
ll ot
her
devi
ces.
•H
ub-a
nd-s
poke
env
iron
men
ts s
houl
d ei
ther
hav
e th
e D
R a
s th
e hu
b or
be
confi
gure
d us
ing
poin
t-to
-poi
nt s
ubin
terf
aces
.•
Part
ial m
esh
envi
ronm
ents
sho
uld
be c
onfig
ured
usi
ng p
oint
-to-
poin
t sub
inte
rfac
es,
espe
cial
ly w
hen
no s
ingl
e de
vice
has
ful
l con
nect
ivit
y to
all
othe
r de
vice
s. I
f th
ere
is a
sub
set
of t
he t
opol
ogy
wit
h fu
ll c
onne
ctiv
ity,
the
n th
at s
ubse
t ca
n us
e a
mul
tipo
int
subi
nter
face
.•
Full
mes
h en
viro
nmen
ts c
an b
e co
nfigu
red
on t
he m
ain
inte
rfac
e, b
ut o
ften
logi
cal
inte
rfac
es a
re u
sed
to t
ake
adva
ntag
e of
the
oth
er b
enefi
ts o
f su
bint
erfa
ces.
OSP
F su
ppor
ts fi
ve n
etw
ork
type
s:•
NB
MA
—D
efau
lt f
or m
ulti
poin
t se
rial
inte
rfac
es. R
FC-c
ompl
iant
mod
e th
at u
ses
DR
s an
d re
quir
es m
anua
l nei
ghbo
r co
nfigu
rati
on.
•Po
int-
to–m
ultip
oint
(P2M
P)—
Doe
sn’t
use
DR
s so
adj
acen
cies
incr
ease
loga
rith
mic
ally
w
ith r
oute
rs. R
esili
ent R
FC c
ompl
iant
mod
e th
at a
utom
atic
ally
dis
cove
rs n
eigh
bors
.•
Poin
t-to
-mul
tipo
int
nonb
road
cast
(P2
MN
B)—
Prop
riet
ary
mod
e th
at is
use
d on
L
ayer
2 f
acili
ties
whe
re d
ynam
ic n
eigh
bor
disc
over
y is
not
sup
port
ed. R
equi
res
man
ual n
eigh
bor
confi
gura
tion
.
•B
road
cast
—D
efau
lt m
ode
for
LA
Ns.
Use
s D
Rs
and
auto
mat
ic n
eigh
bor
disc
over
y.
Prop
riet
ary
whe
n us
ed o
n W
AN
inte
rfac
e.•
Poin
t-to
–poi
nt (P
2P)—
Prop
riet
ary
mod
e th
at d
isco
vers
nei
ghbo
rs a
nd d
oesn
’t us
e D
R.
The
inte
rfac
e ty
pe is
sel
ecte
d—as
sum
ing
the
defa
ult
is u
nsat
isfa
ctor
y—us
ing
the
com
man
d ip
osp
f ne
twor
k:Router(config-if)# ip ospf network point-to-multipoint
Whe
n us
ing
the
NB
MA
or
P2M
P no
n-br
oadc
ast
mod
e, n
eigh
bors
mus
t be
man
ually
de
fined
und
er t
he r
outi
ng p
roce
ss:
Router(config-router)# neighbor 172.16.0.1
Mo
de
RFC
or
Cis
co
DR
Ad
jace
ncie
s
Ne
igh
bo
r
Dis
co
ve
ry
Tim
ers
He
llo
/De
ad
To
po
NB
MA
RFC
Yes
2n–3
Man
ual
30/1
20Fu
ll
P2M
PR
FCN
on(
n–1)
/2A
utom
atic
30/1
20A
ny
P2M
PNB
Cis
coN
on(
n–1)
/2M
anua
l30
/120
Any
Bro
adca
stC
isco
Yes
2n–3
Aut
omat
ic10
/40
Full
P2P
Cis
coN
o1
Aut
omat
ic10
/40
P2P
0910_BSCIssf.fm Page 241 Tuesday, September 9, 2003 8:24 AM
242 BSCI Quick Reference SheetsO
SP
F A
dvert
isem
en
ts a
nd
Co
st
LS
A T
yp
es
OSP
F ad
vert
ises
man
y di
ffer
ent
thin
gs in
dif
fere
nt w
ays.
The
typ
e of
adv
erti
sem
ent
esta
blis
hes
cont
ext
for
its
cont
ents
.
Co
st
By
defa
ult,
Cis
co a
ssig
ns a
cos
t to
eac
h in
terf
ace
that
is in
vers
ely
prop
orti
onal
to
100
Mbp
s.
The
def
ault
form
ula
does
n’t d
iffer
entia
te b
etw
een
fast
eth
erne
t and
gig
abit
ethe
rnet
, for
ex
ampl
e. In
suc
h ca
ses,
the
cost
form
ula
can
be a
djus
ted
usin
g th
e au
to-c
ost c
omm
and.
V
alue
s fo
r ba
ndw
idth
(in
Kb)
up
to 4
,294
,967
are
per
mit
ted
(1 G
b is
sho
wn
in t
he
exam
ple)
.Router(config-router)# auto-cost reference-bandwidth 1000000
The
cos
t ca
n al
so b
e m
anua
lly a
ssig
ned
unde
r in
terf
ace
confi
gura
tion
mod
e. C
ost
is a
16
-bit
num
ber,
so c
an b
e an
y va
lue
up t
o 65
,535
.Router(config-router)# ip ospf cost 27
OS
PF S
um
mari
zati
on
OS
PF B
en
efi
ts o
f S
um
mari
zati
on
All
rout
ing
prot
ocol
s be
nefit
from
sum
mar
izat
ion,
but
OSP
F es
peci
ally
ben
efits
bec
ause
it
is a
lrea
dy s
ensi
tive
to th
e m
emor
y an
d C
PU s
peed
of t
he r
oute
rs. S
umm
ariz
atio
n pr
even
ts
topo
logy
cha
nges
fro
m b
eing
pas
sed
outs
ide
an a
rea
and
thus
sav
es r
oute
rs in
oth
er
area
s fr
om h
avin
g to
run
the
SPF
alg
orit
hm. O
SPF
can
prod
uce
sum
mar
ies
wit
hin
a cl
assf
ul n
etw
ork
(VL
SM)
or s
umm
arie
s of
blo
cks
of c
lass
ful n
etw
orks
(C
IDR
).
Cre
ati
ng
a S
um
mary
Inte
r-ar
ea s
umm
ariz
atio
ns a
re c
reat
ed o
n th
e A
BR
und
er t
he r
oute
r pr
oces
s us
ing
the
area
ran
ge c
omm
and.
The
follo
win
g co
mm
and
adve
rtis
es 1
72.1
6.0.
0/12
from
are
a ze
ro.
Router(config-router)# area 0 range 172.16.0.0 255.240.0.0
Sum
mar
izin
g ex
tern
al r
oute
s is
don
e on
an
ASB
R w
ith th
e su
mm
ary-
addr
ess
com
man
d un
der
the
rout
ing
proc
ess.
The
fol
low
ing
exam
ple
sum
mar
izes
a r
ange
of
exte
rnal
ro
utes
to
192.
168.
0.0/
16 a
nd in
ject
s a
sing
le r
oute
into
OSP
F.Router(config-router)# summary-address 192.168.0.0 255.255.0.0
Cre
ati
ng
a D
efa
ult
Ro
ute
The
def
ault
rou
te is
a s
peci
al t
ype
of s
umm
ariz
atio
n—it
sum
mar
izes
eve
ryth
ing.
Thi
s pr
ovid
es t
he u
ltim
ate
bene
fit o
f su
mm
ariz
atio
n by
red
ucin
g th
e ro
utin
g in
form
atio
n to
a
min
imum
. Sev
eral
dif
fere
nt w
ays
to u
se t
he r
oute
r IO
S to
pla
ce a
def
ault
rou
te in
to
OSP
F.T
he b
est-
know
n w
ay t
o pr
oduc
e an
OSP
F de
faul
t is
to
use
the
defa
ult-
info
rmat
ion
com
man
d:Router(config-router)# default-information originate [always]
Typ
eD
escri
pti
on
Ro
uti
ng
Tab
le
Sym
bo
l
1In
tra-
area
LSA
of
a ro
uter
O
2In
tra-
area
LSA
of
DR
O
3In
ter-
area
rou
te p
asse
d by
AB
RO
IA
4In
ter-
area
rou
te t
o an
ASB
RO
IA
5E
xter
nal t
ype
2 ro
ute
from
ASB
R. M
etri
c do
esn’
t ac
crue
in O
SPF
(def
ault
).O
E2
5E
xter
nal t
ype
1 ro
ute
from
ASB
R. M
etri
c ac
cum
ulat
es
in O
SPF.
O E
1
6M
ulti
cast
(no
t us
ed b
y C
isco
)N
/A
7N
ot-s
o-st
ubby
are
a (N
SSA
) ex
tern
al r
oute
pas
sed
thro
ugh
stub
by a
rea
O N
2O
N1
Cost=
100Mbps
Bandwidth
0910_BSCIssf.fm Page 242 Tuesday, September 9, 2003 8:24 AM
IS-IS 243
Thi
s co
mm
and,
wit
hout
the
key
wor
d al
way
s, r
eadv
erti
ses
a de
faul
t le
arne
d fr
om
anot
her
sour
ce in
to O
SPF.
If
the
alw
ays
keyw
ord
is p
rese
nt, O
SPF
adve
rtis
es a
def
ault
ev
en if
one
doe
s no
t al
read
y ex
ist.
A d
efau
lt s
umm
ary
can
also
be
prod
uced
usi
ng t
he s
umm
ary-
addr
ess
com
man
d or
the
ar
ea r
ange
com
man
d (t
o ju
st p
rodu
ce a
def
ault
into
an
area
). R
educ
ing
rout
ing
info
r-m
atio
n in
non
-bac
kbon
e ar
eas
is a
com
mon
req
uire
men
t be
caus
e th
ese
rout
ers
are
the
mos
t vul
nera
ble,
in te
rms
of p
roce
ssor
and
spe
ed, a
nd th
e lin
ks th
at c
onne
ct th
em h
ave
the
leas
t ban
dwid
th. A
spe
cific
con
cern
is th
at a
n ar
ea w
ill b
e ov
erw
helm
ed b
y ex
tern
al
rout
ing
info
rmat
ion.
Mak
ing
an a
rea
a st
ub a
rea
forc
es it
s A
BR
to
drop
all
exte
rnal
(ty
pe 5
) ro
utes
and
re
plac
es t
hem
wit
h a
defa
ult
rout
e. I
n so
me
case
s an
are
a ca
n be
mad
e to
tally
stu
bby
(stu
b no
-sum
mar
y), i
n w
hich
cas
e al
l int
ra-a
rea
and
exte
rnal
rou
tes
are
repl
aced
by
a de
faul
t.Router(config-router)# area 7 stub [no-summary]
Stub
are
as a
re a
ttra
ctiv
e be
caus
e of
the
ir lo
w o
verh
ead.
The
y do
hav
e so
me
limit
atio
ns, i
nclu
ding
the
fol
low
ing:
•St
ub a
reas
can
’t in
clud
e a
virt
ual l
ink.
•St
ub a
reas
can
’t in
clud
e an
ASB
R.
•St
ubbi
ness
mus
t be
con
figur
ed o
n al
l rou
ters
in t
he a
rea.
A t
hird
kin
d of
stu
bby
area
is a
not
-so-
stub
by a
rea
(NSS
A).
NSS
A is
like
a s
tub
or
tota
lly s
tub
area
, but
allo
ws
an A
SBR
wit
hin
the
area
. Ext
erna
l rou
tes
are
adve
rtis
ed
as ty
pe 7
rou
tes
and
sent
to th
e A
BR
, whi
ch c
onve
rts
them
to tr
adit
iona
l typ
e 5
exte
rnal
ro
utes
. The
NSS
A a
rea
allo
ws
the
netw
ork
to a
dapt
to y
our
com
pany
’s ph
ysic
al to
polo
gy
and
has
adva
ntag
es in
term
s of
filt
erin
g an
d su
mm
ariz
atio
n of
ext
erna
l rou
tes.
An
NSS
A
area
is id
enti
fied
wit
h th
e ar
ea n
ssa
com
man
d:Router(config-router)# area 7 nssa [no-summary]
IS-I
SIn
term
edia
te S
yste
m-t
o-In
term
edia
te S
yste
m (
IS-I
S) is
a li
nk s
tate
rou
ting
pro
toco
l tha
t is
par
t of t
he O
SI fa
mily
of p
roto
cols
. Int
egra
ted
IS-I
S ca
n ca
rry
IP n
etw
ork
info
rmat
ion,
bu
t do
es n
ot u
se I
P as
its
tran
spor
t pr
otoc
ol. I
t us
es C
LN
S an
d C
LN
P to
del
iver
its
upda
tes.
IS-I
S is
a c
lass
less
inte
rior
gat
eway
pro
toco
l tha
t use
s ro
uter
res
ourc
es e
ffici
ently
, an
d sc
ales
to
very
larg
e ne
twor
ks, s
uch
as la
rge
Inte
rnet
ser
vice
pro
vide
rs (
ISPs
).
IS-I
S A
cro
nym
s
Term
Acro
ny
mD
escri
pti
on
Inte
rmed
iate
Sys
tem
IST
he O
SI n
ame
for
a ro
uter
.
End
sys
tem
ES
A h
ost,
suc
h as
a c
ompu
ter.
Con
nect
ionl
ess
Net
wor
k Se
rvic
es
CN
LS
An
OSI
dat
a de
liver
y se
rvic
e th
at p
rovi
des
best
-eff
ort
deliv
ery.
Con
nect
ionl
ess
Net
wor
k Pr
otoc
olC
LN
PT
he O
SI p
roto
col u
sed
to
prov
ide
the
conn
ecti
onle
ss
serv
ices
.
End
sys
tem
hel
loE
SHSe
nt b
y ho
sts
to r
oute
rs.
Inte
rmed
iate
Sys
tem
hel
loIS
HSe
nt b
y ro
uter
s to
hos
ts.
IS t
o IS
hel
loII
HH
ello
s ex
chan
ged
betw
een
rout
ers.
Sep
arat
e le
vel 1
and
le
vel 2
IIH
s ex
ist.
Type
Len
gth
Val
ueT
LVFi
elds
in th
e IS
-IS
upda
tes
that
co
ntai
n IP
sub
net,
au
then
tica
tion
, and
end
sy
stem
info
rmat
ion.
Net
wor
k Se
rvic
e A
cces
s Po
int
NSA
PT
he a
ddre
ss o
f a C
LN
S de
vice
. A
ddre
sses
are
ass
igne
d pe
r de
vice
, not
per
inte
rfac
e as
w
ith
IP.
0910_BSCIssf.fm Page 243 Tuesday, September 9, 2003 8:24 AM
244 BSCI Quick Reference SheetsTyp
es o
f IS
-IS
Ro
ute
rsA
n IS
-IS
netw
ork
is d
ivid
ed in
to a
reas
. With
in a
n ar
ea, r
oute
rs c
an b
e on
e of
thre
e ty
pes:
•L
evel
1 (
L1)
rou
ter—
Rou
tes
to n
etw
orks
onl
y w
ithi
n th
e lo
cal a
rea
(int
ra-a
rea
rout
ing)
. Use
s a
defa
ult r
oute
to th
e ne
ares
t Lev
el 2
rou
ter
for
traf
fic b
ound
out
side
th
e ar
ea. R
outi
ng is
bas
ed o
n Sy
stem
ID
. Kee
ps o
ne L
SDB
for
the
loca
l are
a. (
R1,
R
2, a
nd R
5 in
thi
s fig
ure.
)
•L
evel
2 (
L2)
rou
ter—
Rou
tes
to n
etw
orks
in o
ther
are
as (
inte
rare
a ro
utin
g). T
he
rout
ing
is b
ased
on
area
ID
. Kee
ps o
ne L
SDB
for
rou
ting
to
othe
r ar
eas.
(R
6 in
th
is fi
gure
.)•
Lev
el 1
-2 (
L1-
2) r
oute
r—A
cts
as a
gat
eway
into
and
out
of
an a
rea.
Doe
s L
evel
1
rout
ing
wit
hin
the
area
and
Lev
el 2
rou
ting
bet
wee
n ar
eas.
Kee
ps t
wo
LSD
B, o
ne
for
the
loca
l are
a an
d on
e fo
r in
tera
rea
rout
ing.
(R3
and
R4
in th
is fi
gure
.)T
he IS
-IS
back
bone
is n
ot a
spe
cific
are
a, a
s in
OSP
F, b
ut a
n un
brok
en c
hain
of r
oute
rs
doin
g L
evel
2 r
outi
ng. R
3, R
6, a
nd R
4 ar
e th
e ba
ckbo
ne in
thi
s fig
ure.
Term
Acro
nym
Descri
pti
on
Net
wor
k E
ntit
y T
itle
NE
TA
rou
ter’
s N
SAP.
The
last
byt
e of
a N
ET
is a
lway
s ze
ro.
NSA
P Se
lect
orN
SEL
The
last
byt
e of
a N
SAP
addr
ess.
Ide
ntifi
es t
he p
roce
ss
on t
he d
evic
e, s
uch
as r
outi
ng.
Lin
k St
ate
PDU
LSP
A r
outi
ng u
pdat
e.
Subn
etw
ork
Poin
t of
Att
achm
ent
SNPA
Lay
er 2
iden
tific
atio
n fo
r a
rout
er’s
inte
rfac
e, s
uch
as
MA
C a
ddre
ss o
r D
LC
I.
Cir
cuit
ID
Iden
tifie
s a
phys
ical
inte
rfac
e on
the
rou
ter.
Lin
k St
ate
Dat
abas
eL
SDB
Sequ
ence
Num
ber
Prot
ocol
Dat
a U
nit
SNP
An
IS-I
S pa
cket
tha
t is
se
quen
ced
and
mus
t be
ac
know
ledg
ed. T
he s
eque
nce
num
ber
help
s a
rout
er
mai
ntai
n th
e m
ost
rece
nt li
nk
stat
e in
form
atio
n.
Com
plet
e Se
quen
ce N
umbe
r PD
UC
SNP
A s
umm
ary
of a
rou
ter’s
co
mpl
ete
Lin
k St
ate
Dat
abas
e.
Part
ial S
eque
nce
Num
ber
PDU
PSN
PU
sed
to a
ckno
wle
dge
rece
ipt
of a
CSN
P an
d to
req
uest
m
ore
info
rmat
ion
abou
t a
netw
ork
cont
aine
d in
a C
SNP.
Part
ial r
oute
cal
cula
tion
PRC
Use
d to
det
erm
ine
end
syst
em
and
IP s
ubne
t re
acha
bilit
y.
R1-
L1
R2-
L1R
3-L1
-2
R5-
L1
R6-
L2
R4-
L1-2
Are
a49
.000
1
Are
a49
.000
2
Are
a49
.000
3
0910_BSCIssf.fm Page 244 Tuesday, September 9, 2003 8:24 AM
IS-IS 245
NS
AP
Ad
dre
ss S
tru
ctu
re
In C
isco
impl
emen
tatio
n of
inte
grat
ed IS
-IS,
NSA
P ad
dres
ses
have
thre
e pa
rts.
A r
oute
r al
way
s ha
s a
NSE
L o
f 00
. An
area
ID
tha
t be
gins
wit
h 49
des
igna
tes
priv
ate
area
ad
dres
sing
. MA
C a
ddre
sses
or
IP a
ddre
sses
pad
ded
wit
h 0s
are
oft
en u
sed
as s
yste
m ID
s.
Ad
jacen
cy F
orm
ati
on
in
IS
-IS
IS-I
S ro
uter
s fo
rm a
djac
enci
es b
ased
on
the
leve
l of
IS r
outi
ng t
hey
are
doin
g an
d th
eir
area
num
ber.
Thi
s is
a C
LN
S ad
jace
ncy
and
can
be f
orm
ed e
ven
if I
P ad
dres
ses
don’
t m
atch
.•
Lev
el 1
rou
ters
for
m a
djac
enci
es o
nly
wit
h L
1 an
d L
1-2
devi
ces
in t
heir
ow
n ar
ea.
(In
the
prev
ious
figu
re, R
1 w
ith
R2
and
R3.
)•
Lev
el 2
rou
ters
for
m a
djac
enci
es o
nly
wit
h L
evel
2 c
apab
le d
evic
es (
eith
er L
2 or
L
1-2
rout
ers)
. The
se c
an b
e in
the
loca
l are
a or
in o
ther
are
as. (
In t
he p
revi
ous
fig-
ure,
R6
wit
h R
3 an
d R
4•
Lev
el 1
-2 r
oute
rs f
orm
Lev
el 1
adj
acen
cies
wit
h L
1 ro
uter
s in
the
ir o
wn
area
, and
L
evel
2 a
djac
enci
es w
ith
rout
ers
in o
ther
are
as. (
In t
he p
revi
ous
figur
e, R
4 ha
s a
L1
adja
cenc
y w
ith
R5
and
a L
2 ad
jace
ncy
wit
h R
6.)
IS-I
S in
a B
road
cast,
Mu
ltia
ccess N
etw
ork
On
a ne
twor
k su
ch a
s E
ther
net,
IS-
IS r
oute
rs e
lect
a D
esig
nate
d In
term
edia
te S
yste
m
(DIS
). T
he D
IS is
ele
cted
bas
ed o
n pr
iori
ty, w
ith
MA
C a
ddre
ss a
s th
e ti
ebre
aker
. Rou
t-er
s fo
rm a
djac
enci
es w
ith
all r
oute
rs o
n th
e L
AN
as
wel
l as
the
DIS
. The
DIS
cre
ates
a
pseu
dono
de t
o re
pres
ent
the
netw
ork
and
send
s ou
t an
adv
erti
sem
ent
to r
epre
sent
the
L
AN
. All
rout
ers
adve
rtis
e on
ly a
n ad
jace
ncy
to t
he p
seud
onod
e. I
f th
e D
IS f
ails
, an
othe
r is
ele
cted
; no
back
up D
IS e
xist
s. T
he D
IS s
ends
Hel
los
ever
y 3.
3 se
cond
s; o
ther
ro
uter
s se
nd t
hem
eve
ry 1
0 se
cond
s. T
he D
IS a
lso
mul
tica
sts
a C
SNP
ever
y 10
sec
onds
.
IS-I
S o
n a
Po
int-
to-P
oin
t Lin
kN
o D
IS e
xist
s on
a p
oint
-to-
poin
t lin
k. W
hen
an a
djac
ency
is fi
rst
form
ed o
ver
the
link,
th
e ro
uter
s ex
chan
ge C
SNPs
. If
one
of t
he r
oute
rs n
eeds
mor
e in
form
atio
n ab
out
a sp
ecifi
c ne
twor
k, it
sen
ds a
PSN
P re
ques
ting
tha
t. A
fter
the
init
ial e
xcha
nge,
LSP
s ar
e se
nt t
o de
scri
be li
nk c
hang
es, a
nd t
hey
are
ackn
owle
dged
wit
h PS
NPs
.
IS-I
S C
on
fig
ura
tio
n T
asks
•E
nabl
e IS
-IS
on t
he r
oute
r.•
Con
figur
e ea
ch r
oute
r’s N
ET.
•E
nabl
e IS
-IS
on t
he r
oute
r’s in
terf
aces
.
Basic
IS
-IS
Co
mm
an
ds
Are
a ID
—1
to 1
3 by
tes
long
Syst
em I
D—
Mus
t be
exa
ctly
6 b
ytes
long
NSE
L—
1 by
te
Co
mm
an
dD
escri
pti
on
rout
er is
isE
nabl
es I
S-IS
on
the
rout
er
net
Ass
igns
the
rou
ter’s
NSA
P ad
dres
s
ip r
oute
r is
isE
nabl
es I
S-IS
on
an in
terf
ace
is-t
ype
Sets
the
IS
leve
l for
the
who
le r
oute
r
isis
cir
cuit
-typ
eSe
ts t
he I
S le
vel f
or a
n in
terf
ace
isis
met
ric
Cha
nges
the
met
ric
for
an in
terf
ace
sum
mar
y-ad
dres
sSu
mm
ariz
es I
P ne
twor
ks f
or I
S-IS
show
isis
top
olog
yD
ispl
ays
the
topo
logy
dat
abas
e an
d le
ast
cost
pat
hs
show
cln
s ro
ute
Dis
play
s th
e L
2 ro
utin
g ta
ble
show
isis
rou
teD
ispl
ays
the
L1 r
outin
g ta
ble—
requ
ires
CLN
S ro
utin
g en
able
d
show
cln
s pr
otoc
olD
ispl
ays
the
rout
er’s
IS t
ype,
sys
tem
ID
, are
a ID
, int
erfa
ces
runn
ing
IS-I
S, a
nd a
ny r
edis
trib
utio
n
show
cln
s ne
ighb
ors
Dis
play
s th
e ad
jace
nt n
eigh
bors
and
the
ir I
S le
vel
show
cln
s in
terf
ace
Dis
play
s IS
-IS
deta
ils f
or e
ach
inte
rfac
e, s
uch
as c
ircu
it
type
, met
ric,
and
pri
orit
y
show
ip p
roto
cols
Dis
play
s th
e in
tegr
ated
IS-
IS s
etti
ngs
0910_BSCIssf.fm Page 245 Tuesday, September 9, 2003 8:24 AM
246 BSCI Quick Reference SheetsTu
nin
g IS
-IS
You
nee
d to
do
thre
e ba
sic
type
s of
tun
ing
to I
S-IS
rou
ters
:•
Set
the
IS le
vel.
•Se
t th
e ci
rcui
t ty
pe o
n L
1-2
rout
ers.
•Su
mm
ariz
e ad
dres
ses.
Sett
ing
th
e IS
Level
Cis
co r
oute
rs a
re L
1-2
by d
efau
lt. I
f th
e ro
uter
is c
ompl
etel
y an
inte
rnal
are
a ro
uter
, se
t th
e IS
leve
l to
L1.
If
the
rout
er r
oute
s on
ly t
o ot
her
area
s an
d ha
s no
inte
rnal
are
a in
terf
aces
, set
the
IS
leve
l to
L2.
If
the
rout
er h
as b
oth
inte
rnal
and
ext
erna
l are
a in
ter-
face
s, le
ave
the
IS le
vel a
t L
1-2.
Sett
ing
th
e C
ircu
it T
yp
e
On
L1-
2 ro
uter
s, a
ll in
terf
aces
sen
d ou
t bot
h L
1 an
d L
2 he
llos,
tryi
ng to
est
ablis
h bo
th
type
s of
adj
acen
cies
. Thi
s ca
n w
aste
ban
dwid
th. I
f on
ly a
n L
1 ro
uter
is a
ttac
hed
to a
n in
terf
ace,
the
n ch
ange
the
cir
cuit
typ
e fo
r th
at in
terf
ace
to L
1, s
o th
at o
nly
L1
hello
s ar
e se
nt. I
f the
re is
onl
y a
L2
rout
er a
ttac
hed
to a
n in
terf
ace,
cha
nge
the
circ
uit t
ype
for
that
inte
rfac
e to
L2.
Su
mm
ari
zin
g A
dd
resses
Alt
houg
h IS
-IS
does
CL
NS
rout
ing,
it c
an s
umm
ariz
e th
e IP
add
ress
es t
hat
it c
arri
es.
Sum
mar
ized
rou
tes
can
be d
esig
nate
d as
Lev
el 1
, Lev
el 2
, or
Lev
el 1
-2 r
oute
s. T
he
defa
ult
is L
evel
2.
Op
tim
izin
g R
ou
tin
g
Mig
rati
ng
IP
Ad
dre
ssin
gM
ost
netw
orks
ope
rate
mor
e ef
ficie
ntly
whe
n us
ing
a m
oder
n ro
utin
g pr
otoc
ol. W
hen
mig
rati
ng to
a n
ew r
outi
ng p
roto
col,
you
mig
ht a
lso
need
to c
hang
e IP
add
ress
sch
emes
. Y
ou o
ften
cha
nge
IP a
ddre
ssin
g w
hen
mov
ing
from
a F
LSM
pro
toco
l to
a V
LSM
one
, or
to c
reat
e ro
ute
sum
mar
y po
ints
with
in th
e ne
twor
k. H
ere
are
som
e ar
eas
to c
onsi
der
whe
n pl
anni
ng t
his:
•H
ost
addr
esse
s—C
hang
e or
add
DH
CP.
•N
AT
—T
rans
late
the
new
add
ress
es.
•D
NS
serv
ers—
If s
erve
r ha
ve n
ew a
ddre
sses
, new
DN
S m
appi
ngs
mad
e ne
ed t
o be
co
nfigu
red.
•A
cces
s lis
ts a
nd fi
rew
alls
—U
pdat
e tr
affic
filt
ers
to w
ork
for
the
new
add
ress
es.
•R
outi
ng—
Upd
ate
rout
ers
to r
oute
for
the
new
net
wor
ks.
•Se
cond
ary
addr
essi
ng—
You
mig
ht n
eed
to h
ave
both
old
and
new
add
ress
es o
n th
e ro
uter
inte
rfac
es d
urin
g tr
ansi
tion
.•
Tim
ing
of t
he t
rans
itio
n—W
ho g
ets
conv
erte
d w
hen.
Con
side
rs t
he d
ay o
f th
e w
eek
and
tim
e of
day
.•
Tra
nsit
ion
stra
tegy
—W
hich
par
ts o
f th
e ne
twor
k ar
e ch
ange
d fir
st, s
econ
d, e
tc.
How
to
avoi
d di
srup
ting
use
r tr
affic
dur
ing
the
tran
siti
on.
Mig
rati
ng
Ro
uti
ng
Pro
toco
lsT
he s
teps
in m
igra
ting
to
a ne
w r
outi
ng p
roto
col a
re a
s fo
llow
s:St
ep 1
Dec
ide
on a
tim
elin
e fo
r th
e m
igra
tion
.
Step
2Id
enti
fy b
ound
ary
rout
ers
that
are
to
run
both
pro
toco
ls.
Step
3D
ecid
e w
hich
pro
toco
l is
to b
e th
e co
re a
nd w
hich
is to
be
the
edge
pro
toco
l.
Step
4D
ecid
e w
here
and
in w
hat
dire
ctio
n to
red
istr
ibut
e ro
utes
.
Step
5Te
st t
he p
lan
in a
lab.
Step
6B
ack
up a
ll de
vice
con
figur
atio
ns b
efor
e ch
angi
ng t
hem
.
Rou
te r
edis
trib
utio
n ca
n ca
use
prob
lem
s be
caus
e of
rou
te f
eedb
ack,
inco
mpa
tibl
e m
etri
cs, a
nd in
cons
iste
nt c
onve
rgen
ce t
imes
. The
saf
est
way
to
run
mul
tipl
e pr
otoc
ols
is t
o re
dist
ribu
te th
e ed
ge p
roto
col i
nto
the
core
, and
sen
d a
defa
ult r
oute
or
use
stat
ic
rout
ing
back
to
the
edge
. The
nex
t be
st w
ay is
to
redi
stri
bute
bot
h w
ays
and
filte
r to
av
oid
rout
e fe
edba
ck d
ista
nce,
or
chan
ge t
he a
dmin
istr
ativ
e di
stan
ce o
f re
dist
ribu
ted
rout
es.
Edg
eP
roto
col
Cor
eP
roto
col
Red
istr
ibut
eE
dge
into
Cor
e
Wha
t to
Do
inth
is D
irect
ion?
0910_BSCIssf.fm Page 246 Tuesday, September 9, 2003 8:24 AM
Optimizing Routing 247
Eac
h pr
otoc
ol h
as s
ome
uniq
ue c
hara
cter
isti
cs w
hen
redi
stri
buti
ng, a
s sh
own
in t
he
follo
win
g ta
ble.
Seed
Metr
icR
edis
trib
utio
n in
volv
es c
onfig
urin
g a
rout
ing
prot
ocol
to
adve
rtis
e ro
utes
lear
ned
by
anot
her
rout
ing
proc
ess.
Pro
toco
ls u
se in
com
pati
ble
met
rics
, so
the
redi
stri
bute
d ro
utes
mus
t be
ass
igne
d a
new
met
ric
com
pati
ble
wit
h th
e ne
w p
roto
col.
Nor
mal
ly,
met
rics
are
bas
ed o
n an
inte
rfac
e va
lue,
suc
h as
ban
dwid
th, b
ut n
o in
terf
ace
for
a re
dist
ribu
ted
rout
e ex
ists
. A r
oute
’s or
igin
al m
etri
c is
cal
led
its
seed
met
ric.
Set
the
met
ric
for
all r
edis
trib
uted
rou
tes
wit
h th
e de
faul
t-m
etri
c [m
etri
c] c
omm
and.
To
set
the
met
ric
for
spec
ific
rout
es, e
ithe
r us
e th
e m
etri
c ke
ywor
d w
hen
redi
stri
buti
ng
or u
se t
he r
oute
-map
key
wor
d to
link
a r
oute
map
to
the
redi
stri
buti
on.
Co
nfi
gu
rin
g R
ou
te R
ed
istr
ibu
tio
nY
ou c
an r
edis
trib
ute
betw
een
prot
ocol
s th
at u
se t
he s
ame
prot
ocol
sta
ck, e
.g.,
IP
prot
ocol
s ca
nnot
adv
erti
se I
PX r
oute
s. C
onfig
urin
g re
dist
ribu
tion
is s
impl
e; is
sue
this
com
man
d un
der
the
rout
ing
proc
ess
that
is t
o re
ceiv
e th
e ne
w r
oute
s:redistribute [route source]
To
ols
fo
r C
on
tro
llin
g/P
reven
tin
g R
ou
tin
g U
pd
ate
s•
Pass
ive
inte
rfac
e•
Def
ault
and
/or
stat
ic r
oute
s•
Dis
trib
ute
list
•R
oute
map
•C
hang
e ad
min
istr
ativ
e di
stan
ce
Pa
ssiv
e I
nte
rfa
ce
Pass
ive
inte
rfac
e pr
even
ts R
IP a
nd I
GR
P fr
om s
endi
ng u
pdat
es o
ut a
n in
terf
ace.
It
pre-
vent
s ot
her
rout
ing
prot
ocol
s fr
om s
endi
ng h
ello
s ou
t of
an
inte
rfac
e; t
hus,
the
y do
n’t
disc
over
nei
ghbo
rs o
r fo
rm a
n ad
jace
ncy
out
that
inte
rfac
e. R
IP, I
GR
P, a
nd o
lder
ver
-si
ons
of E
IGR
P re
quir
e a
clas
sful
net
wor
k in
the
net
wor
k st
atem
ent.
To
avoi
d ru
nnin
g th
e pr
otoc
ol a
ll in
terf
aces
wit
hin
that
net
wor
k, u
se th
e pa
ssiv
e-in
terf
ace
com
man
d an
d sp
ecif
y an
inte
rfac
e th
at d
oesn
’t ru
n th
e pr
otoc
ol. T
o tu
rn o
ff t
he p
roto
col o
n al
l int
er-
face
s, u
se p
assi
ve-i
nter
face
def
ault,
the
n no
pas
sive
-int
erfa
ce f
or t
he o
nes
that
sho
uld
run
the
prot
ocol
.
Dis
trib
ute
Lis
tsA
dis
trib
ute
list
allo
ws
you
to fi
lter
rou
ting
upd
ates
thr
ough
an
acce
ss li
st. C
onfig
ure
an a
cces
s lis
t and
then
link
that
acc
ess
list t
o th
e ro
utin
g pr
oces
s w
ith
the
dist
ribu
te-l
ist
com
man
d.T
he d
istr
ibut
e-lis
t co
mm
and
has
two
opti
ons:
•di
stri
bute
-lis
t [A
CL
] in
—Fi
lter
s up
date
s as
the
y co
me
in a
n in
terf
ace.
For
OSP
F,
this
con
trol
s ro
utes
pla
ced
in t
he r
outi
ng t
able
but
not
the
dat
abas
e. F
or o
ther
pr
otoc
ols,
thi
s co
ntro
ls t
he r
oute
s th
e pr
otoc
ol k
now
s ab
out.
•di
stri
bute
-lis
t [A
CL
] ou
t—Fi
lter
s up
date
s go
ing
out
of a
n in
terf
ace
and
also
up
date
s be
ing
redi
stri
bute
d in
fro
m a
noth
er p
roto
col.
Ro
ute
Map
sR
oute
map
s m
atch
con
diti
ons,
and
the
n se
t op
tion
s fo
r tr
affic
tha
t m
atch
es. E
ach
stat
emen
t has
a s
eque
nce
num
ber,
stat
emen
ts a
re r
ead
from
the
low
est n
umbe
r to
hig
hest
,
Ro
ute
Red
istr
ibu
tio
n C
har
acte
rist
ics
RIP
Met
ric
mus
t be
set
exc
ept
whe
n re
dist
ribu
ting
sta
tic
or
conn
ecte
d ro
utes
, whi
ch h
ave
a m
etri
c of
1.
OSP
FD
efau
lt m
etri
c is
20.
Can
spe
cify
the
met
ric
type
; the
def
ault
is
E2.
Mus
t us
e su
bnet
s ke
ywor
d or
onl
y cl
assf
ul n
etw
orks
ar
e re
dist
ribu
ted.
EIG
RP
Met
ric
mus
t be
set
, exc
ept
whe
n re
dist
ribu
ting
sta
tic
or
conn
ecte
d ro
utes
, whi
ch g
et t
heir
met
ric
from
the
inte
rfac
e.
Met
ric
valu
e is
“ba
ndw
idth
, del
ay, r
elia
bilit
y, lo
ad, M
TU
.”
Red
istr
ibut
ed r
oute
s ha
ve a
hig
her
adm
inis
trat
ive
dist
ance
th
an in
tern
al o
nes.
IS-I
SD
efau
lt m
etri
c is
0. C
an s
peci
fy r
oute
leve
l; de
faul
t is
L2.
Can
ch
oose
to
redi
stri
bute
onl
y ex
tern
al o
r in
tern
al r
oute
s in
to I
S-IS
fro
m O
SPF
and
into
OSP
F fr
om I
S-IS
.
Stat
ic/C
onne
cted
Onl
y ro
utes
tha
t ar
e in
the
rou
ting
tab
le a
nd le
arne
d vi
a th
e sp
ecifi
ed p
roto
col a
re r
edis
trib
uted
. To
incl
ude
loca
l ne
twor
ks, y
ou m
ust
redi
stri
bute
con
nect
ed in
terf
aces
. You
ca
n al
so r
edis
trib
ute
stat
ic r
oute
s in
to a
dyn
amic
pro
toco
l.
0910_BSCIssf.fm Page 247 Tuesday, September 9, 2003 8:24 AM
248 BSCI Quick Reference Sheetsan
d th
e ro
uter
sto
ps r
eadi
ng w
hen
it g
ets
a m
atch
. The
seq
uenc
e nu
mbe
r ca
n be
use
d to
inse
rt o
r de
lete
sta
tem
ents
. Her
e ar
e so
me
uses
for
rou
te m
aps:
•Fi
lter
ing
redi
stri
bute
d ro
utes
—U
se t
he r
oute
-map
key
wor
d in
the
red
istr
ibut
e co
mm
and.
•N
AT
—To
spe
cify
the
pri
vate
add
ress
es t
o be
tra
nsla
ted.
•Po
licy-
base
d ro
utin
g—To
spe
cify
whi
ch t
raffi
c sh
ould
be
polic
y ro
uted
, bas
ed o
n ve
ry g
ranu
lar
cont
rols
.•
BG
P po
licy—
To c
ontr
ol r
outi
ng u
pdat
es a
nd t
o m
anip
ulat
ion
path
att
ribu
tes.
Ro
ute
Map
Syn
tax
Rou
te m
aps
are
crea
ted
wit
h th
e co
mm
and:
route-map [name] permit
| deny [sequence no.]
Eac
h st
atem
ent
in a
rou
te m
ap b
egin
s th
is s
ame
way
, wit
h th
e sa
me
rout
e m
ap n
ame
but d
iffe
rent
seq
uenc
e nu
mbe
rs, a
nd w
ith
mat
ch a
nd/o
r se
t con
diti
ons
belo
w it
. Per
mit
m
eans
tha
t an
y tr
affic
mat
chin
g th
e m
atch
con
diti
ons
is u
sed.
Den
y m
eans
tha
t an
y tr
affic
mat
chin
g th
e m
atch
con
diti
ons
is n
ot u
sed.
Matc
h a
nd
Set
Co
nd
itio
ns
Eac
h ro
ute
map
sta
tem
ent
can
have
fro
m n
one
to m
ulti
ple
mat
ch a
nd s
et li
nes.
If
no
mat
ch li
ne e
xist
s, t
he s
tate
men
t m
atch
es a
nyth
ing,
sim
ilar
to a
“pe
rmit
any
” in
an
acce
ss li
st. I
f the
re is
no
set l
ine,
the
mat
chin
g tr
affic
is e
ithe
r pe
rmit
ted
or d
enie
d, w
ith
no o
ther
con
diti
ons
bein
g se
t.M
ulti
ple
mat
ch c
ondi
tion
s on
the
sam
e lin
e us
e a
logi
cal O
R. F
or e
xam
ple,
the
rou
ter
inte
rpre
ts m
atch
a b
c a
s “m
atch
a o
r b
or c
.” M
ulti
ple
mat
ch c
ondi
tion
s on
dif
fere
nt
lines
use
a lo
gica
l AN
D. F
or e
xam
ple,
the
rou
ter
inte
rpre
ts t
he f
ollo
win
g as
“m
atch
a
and
b an
d c”
:mmmmaaaattttcccchhhh aaaa
mmmmaaaattttcccchhhh bbbb
mmmmaaaattttcccchhhh cccc
In r
oute
red
istr
ibut
ion,
her
e ar
e so
me
com
mon
thi
ngs
to m
atch
:•
ip a
ddre
ss—
Ref
ers
the
rout
er t
o an
acc
ess
list
that
per
mit
s or
den
ies
netw
orks
.•
ip n
ext-
hop—
Ref
ers
the
rout
er t
o an
acc
ess
list
that
per
mit
s or
den
ies
next
-hop
IP
addr
esse
s.•
ip r
oute
-sou
rce—
Ref
ers
the
rout
er t
o an
acc
ess
list
that
per
mit
s or
den
ies
adve
rtis
-in
g ro
uter
IP
addr
esse
s.
•m
etri
c—Pe
rmit
s or
den
ies
rout
es w
ith
the
spec
ified
met
ric
from
bei
ng r
edis
trib
-ut
ed.
•ro
ute-
type
—Pe
rmit
s or
den
ies
redi
stri
buti
on o
f th
e ro
ute
type
list
ed, s
uch
as in
ter-
nal o
r ex
tern
al.
•ta
g—R
oute
s ca
n be
labe
led
(tag
ged)
wit
h a
num
ber,
and
rout
e m
aps
can
look
for
th
at n
umbe
r.In
rou
te r
edis
trib
utio
n, s
ome
com
mon
thi
ngs
to s
et a
re•
met
ric—
Sets
the
met
ric
for
redi
stri
bute
d ro
utes
•m
etri
c-ty
pe—
Sets
the
typ
e, s
uch
as E
1 fo
r O
SPF
•ta
g—Ta
gs a
rou
te w
ith
a nu
mbe
r th
at c
an b
e m
atch
ed o
n la
ter
by o
ther
rou
te
map
s•
leve
l—Fo
r IS
-IS,
set
s th
e IS
leve
l for
thi
s ro
ute
Man
ipu
lati
ng
Ad
min
istr
ati
ve D
ista
nce
Whe
n a
rout
er r
ecei
ves
rout
es t
o th
e sa
me
dest
inat
ion
netw
ork
from
mor
e th
an o
ne
rout
ing
proc
ess,
it d
ecid
es w
hich
to
put
in t
he r
outi
ng t
able
by
look
ing
at t
he a
dmin
is-
trat
ive
dist
ance
(A
D)
valu
e as
sign
ed t
o th
e ro
utin
g pr
oces
s. T
he r
oute
wit
h th
e lo
wes
t A
D is
cho
sen.
AD
can
be
chan
ged
for
all r
oute
s of
a p
roce
ss, o
r on
ly fo
r sp
ecifi
c ro
utes
w
ithi
n a
proc
ess.
The
com
man
d is
as
follo
ws:
distance {admin distance} [address mask [ACL]]
Rou
te M
ap E
xam
ple
route-map Demo permit 10
match ip address 23
set metric 550
route-map Demo permit 20
R1
R4
R2
R3
RIP
OS
PF
10.1
.1.0
0910_BSCIssf.fm Page 248 Tuesday, September 9, 2003 8:24 AM
BGP 249
Usi
ng t
he a
ddre
ss/m
ask
keyw
ords
in t
he c
omm
and
chan
ges
the
AD
of
rout
es le
arne
d fr
om t
he n
eigh
bor
wit
h th
at I
P ad
dres
s. S
peci
fyin
g an
acc
ess
list
num
ber
or n
ame
chan
ges
the
AD
onl
y on
net
wor
ks p
erm
itte
d in
the
AC
L. E
IGR
P an
d B
GP
have
dif
fer-
ent
AD
val
ues
for
inte
rnal
and
ext
erna
l rou
tes,
so
you
have
to
list
thos
e se
para
tely
w
hen
usin
g th
e co
mm
and
wit
h th
ose
prot
ocol
s.In
the
pre
viou
s fig
ure,
look
at
the
path
to
the
10.1
.1.0
net
wor
k. R
edis
trib
ute
RIP
into
O
SPF
on R
2. T
hese
rou
tes
inhe
rit O
SPF’
s A
D w
hen
they
are
adv
erti
sed
to R
4. R
4 th
en
adve
rtis
es t
hem
to
R3
as O
SPF
rout
es. W
e ha
ve r
oute
fee
dbac
k. R
3 no
w k
now
s ab
out
the
10.1
.1.0
net
wor
k fr
om t
wo
rout
ing
proc
esse
s: R
IP, w
ith
an A
D o
f 12
0, a
nd O
SPF,
w
ith
an A
D o
f 11
0. T
he p
ath
for
RIP
is t
hrou
gh R
1, t
he s
hort
est
path
. The
pat
h fo
r O
SPF
is t
hrou
gh R
4 an
d R
2, t
hen
to R
1—a
muc
h lo
nger
pat
h. B
ut t
he r
oute
r pu
ts t
he
OSP
F pa
th in
the
rou
ting
tab
le, b
ased
on
AD
.To
pre
vent
thi
s, in
crea
se t
he A
D o
f th
e re
dist
ribu
ted
RIP
rou
tes
whe
n O
SPF
adve
rtis
es
them
. Not
e—th
is d
oesn
’t ch
ange
all
OSP
F ro
utes
, jus
t th
e on
es le
arne
d fr
om R
IP. T
he
com
man
ds, g
iven
on
R2,
are
aaaacccccccceeeessssssss----lllliiiisssstttt 11110000 ppppeeeerrrrmmmmiiiitttt 11110000....1111....1111....0000
rrrroooouuuutttteeeerrrr oooossssppppffff 1111
rrrreeeeddddiiiissssttttrrrriiiibbbbuuuutttteeee rrrriiiipppp ssssuuuubbbbnnnneeeettttssss
ddddiiiissssttttaaaannnncccceeee 111122225555 0000....0000....0000....0000 222255555555....222255555555....222255555555....222255555555 11110000
Now
R3
hear
s ab
out
the
10.1
.1.0
net
wor
k fr
om R
IP w
ith
an A
D o
f 12
0, a
nd f
rom
O
SPF
wit
h an
AD
of
125.
The
RIP
rou
te is
, the
refo
re, p
ut in
to t
he r
outi
ng t
able
.
Po
licy-B
ased
Ro
uti
ng
Rou
ters
nor
mal
ly r
oute
tra
ffic
base
d on
des
tina
tion
net
wor
k. P
olic
y-ba
sed
rout
ing
(PB
R)
over
ride
s th
is a
nd c
ause
s th
em t
o ch
oose
a p
ath
base
d on
the
fol
low
ing:
•Po
rt n
umbe
r of
the
app
licat
ion
used
•Pr
otoc
ol n
umbe
r•
Pack
et s
ize
PBR
lets
you
load
sha
re b
ased
on
char
acte
rist
ics
of t
he t
raffi
c, r
athe
r th
an b
andw
idth
of
the
link
s, a
nd y
ou a
lso
can
set
qual
ity
of s
ervi
ce (
QoS
) va
lues
. It
is a
pplie
d to
pac
k-et
s as
the
y en
ter
the
rout
er, a
nd is
con
figur
ed b
y us
ing
rout
e m
aps.
PB
R B
asic
s1.
Con
figur
e a
rout
e m
ap t
o m
atch
tra
ffic
agai
nst
eith
er a
sta
ndar
d or
ext
ende
d ac
cess
list
, or
pack
et le
ngth
.2.
If t
raffi
c m
atch
es t
he c
ondi
tion
s an
d th
e ro
ute
map
sta
tem
ent
is a
per
mit
, pol
icy
rout
e th
e tr
affic
.
3.If
tra
ffic
mat
ches
the
con
diti
ons
and
the
rout
e m
ap s
tate
men
t is
a d
eny,
do
norm
al r
outi
ng.
4.If
all
the
stat
emen
ts in
the
rou
te m
ap h
ave
been
che
cked
and
no
mat
ch e
xist
s,
rout
e th
e tr
affic
nor
mal
ly (
base
d on
des
tina
tion
).
Co
nfi
gu
rin
g P
BR
You
can
set
the
fol
low
ing
opti
ons
in t
he r
oute
map
:•
ip n
ext-
hop—
The
IP a
ddre
ss o
f the
nex
t hop
rou
ter.
The
rou
ter
chec
ks th
e ro
utin
g ta
ble
to m
ake
sure
thi
s ne
xt h
op is
rea
chab
le.
•in
terf
ace—
The
out
boun
d in
terf
ace
for
the
traf
fic. A
n ex
plic
it r
oute
mus
t al
read
y be
in t
he r
outi
ng t
able
for
the
des
tina
tion
net
wor
k, b
ut t
his
stat
emen
t ov
erri
des
it.
•ip
def
ault
nex
t-ho
p—T
he I
P ad
dres
s of
a n
ext
hop
rout
er t
o se
nd t
raffi
c if
the
re is
no
exp
licit
rou
te f
or t
he d
esti
nati
on n
etw
ork
in t
he r
outi
ng t
able
.•
defa
ult i
nter
face
—T
he o
utbo
und
inte
rfac
e fo
r tr
affic
for
whi
ch th
ere
is n
o ex
plic
it
rout
e in
the
rou
ting
tab
le.
•ip
tos
—Se
ts t
he t
ype
of s
ervi
ce b
its
in t
he I
P he
ader
; use
d fo
r Q
oS p
urpo
ses.
•ip
pre
cede
nce—
Sets
the
pre
cede
nce
valu
e in
the
IP
head
er; u
sed
for
QoS
pur
pose
s.T
he p
olic
y m
ust
be a
pplie
d to
the
inco
min
g in
terf
ace
wit
h th
e co
mm
and
ip p
olic
y ro
ute-
map
<ro
ute
map
nam
e>. V
erif
y th
e po
licy
wit
h th
e fo
llow
ing
com
man
ds:
•sh
ow ip
pol
icy
•pi
ng•
trac
erou
te•
show
rou
te-m
ap <
nam
e>•
debu
g ip
pol
icy
BG
P
BG
P B
asic
s•
BG
P st
ands
for
Bor
der
Gat
eway
Pro
toco
l.•
BG
P us
es t
he c
once
pt o
f au
tono
mou
s sy
stem
s. A
n au
tono
mou
s sy
stem
is a
gro
up
of n
etw
orks
und
er a
com
mon
adm
inis
trat
ion.
•A
uton
omou
s sy
stem
s ru
n In
teri
or G
atew
ay P
roto
cols
(IG
Ps)
wit
hin
the
syst
em.
The
y ru
n an
Ext
erio
r G
atew
ay P
roto
cols
(E
GP)
bet
wee
n th
em.
•B
GP
vers
ion
4 is
the
onl
y E
GP
curr
entl
y in
use
.
0910_BSCIssf.fm Page 249 Tuesday, September 9, 2003 8:24 AM
250 BSCI Quick Reference Sheets•
BG
P ne
ighb
ors
are
calle
d pe
ers
and
mus
t be
sta
tica
lly c
onfig
ured
.•
Use
s T
CP
port
179
.•
BG
P is
a p
ath-
vect
or p
roto
col.
Its
rout
e to
a n
etw
ork
cons
ists
of a
list
of a
uton
omou
s sy
stem
s on
the
pat
h to
tha
t ne
twor
k.•
BG
P’s
loop
pre
vent
ion
mec
hani
sm is
aut
onom
ous
syst
em n
umbe
r. W
hen
an u
pdat
e ab
out a
net
wor
k le
aves
an
auto
nom
ous
syst
em, t
hat a
uton
omou
s sy
stem
’s nu
mbe
r is
pre
pend
ed t
o th
e lis
t of
aut
onom
ous
syst
ems
that
hav
e ha
ndle
d th
at u
pdat
e.
Whe
n an
aut
onom
ous
syst
em r
ecei
ves
an u
pdat
e, it
exa
min
es th
e au
tono
mou
s sy
stem
lis
t. I
f it
find
s it
s ow
n au
tono
mou
s nu
mbe
r in
tha
t lis
t, t
he u
pdat
e is
dis
card
ed.
Exa
mpl
e: I
n th
e fo
llow
ing
figur
e, B
GP
rout
ers
in A
S100
see
net
wor
k 10
.1.1
.0 a
s ha
ving
an
auto
nom
ous
syst
em p
ath
of 2
00 3
00 4
00.
BG
P D
ata
bases
•N
eigh
bor
data
base
—L
ist
of a
ll co
nfigu
red
BG
P ne
ighb
ors.
To
view
, typ
e sh
ow ip
bg
p su
mm
ary.
•B
GP
data
base
, or
RIB
(R
outi
ng I
nfor
mat
ion
Bas
e)—
Lis
t of
net
wor
ks k
now
n by
B
GP,
alo
ng w
ith
thei
r pa
ths
and
attr
ibut
es. T
o vi
ew, t
ype
“sho
w ip
bgp
”.•
Rou
ting
tabl
e—L
ist
of t
he p
aths
to
each
net
wor
k us
ed b
y th
e ro
uter
, and
the
nex
t ho
p fo
r ea
ch n
etw
ork.
To
view
, typ
e sh
ow ip
rou
te.
BG
P M
essag
e T
yp
es
•O
pen
mes
sage
—A
fter
a n
eigh
bor
is c
onfig
ured
, BG
P se
nds
an o
pen
mes
sage
to tr
y to
est
ablis
h a
peer
ing
with
that
nei
ghbo
r. In
clud
es in
form
atio
n su
ch a
s au
tono
mou
s sy
stem
num
ber,
rout
er I
D, a
nd h
old
tim
e.•
Upd
ate
mes
sage
—M
essa
ge u
sed
to t
rans
fer
rout
ing
info
rmat
ion
betw
een
peer
s.•
Kee
paliv
e m
essa
ge—
BG
P pe
ers
exch
ange
kee
paliv
e m
essa
ges
ever
y 60
sec
onds
by
defa
ult.
The
se k
eep
the
peer
ing
sess
ion
acti
ve.
•N
otifi
cati
on m
essa
ge—
If a
pro
blem
occ
urs
that
cau
ses
the
BG
P pe
er t
o be
end
ed,
a no
tific
atio
n m
essa
ge is
sen
t to
the
BG
P ne
ighb
or, a
nd t
he c
onne
ctio
n is
clo
sed.
Inte
rnal an
d E
xte
rnal B
GP
Inte
rnal
BG
P (iB
GP)
is a
BG
P pe
erin
g be
twee
n ro
uter
s in
the
sam
e au
tono
mou
s sy
stem
. E
xter
nal B
GP
(eB
GP)
is a
BG
P pe
erin
g be
twee
n ro
uter
s in
diff
eren
t aut
onom
ous
syst
ems.
B
GP
trea
ts u
pdat
es fr
om in
tern
al p
eers
diff
eren
tly th
an u
pdat
es fr
om e
xter
nal p
eers
.In
thi
s fig
ure,
rou
ters
A a
nd B
are
eB
GP
peer
s. R
oute
rs B
, C a
nd D
are
iBG
P pe
ers.
BG
P S
plit
Ho
rizo
n R
ule
Rou
tes
lear
ned
from
iBG
P ne
ighb
ors
are
not
forw
arde
d to
oth
er iB
GP
neig
hbor
s. B
GP
assu
mes
tha
t al
l int
erna
l BG
P ro
uter
s ar
e fu
lly m
eshe
d, s
o if
one
inte
rnal
rou
ter
has
gott
en a
n up
date
fro
m a
n iB
GP
peer
, all
inte
rnal
rou
ters
sho
uld
have
rec
eive
d it
. Wit
h-ou
t B
GP
split
hor
izon
, rou
ting
loop
s an
d bl
ack
hole
s co
uld
be in
trod
uced
wit
hin
an
auto
nom
ous
syst
em.
For
exam
ple,
in t
he p
revi
ous
figur
e, if
Rtr
B r
ecei
ves
an u
pdat
e fr
om R
trA
, it
forw
ards
th
e up
date
to
Rtr
C a
nd R
trD
. But
C a
nd D
do
not
send
it b
ack
to B
, or
to e
ach
othe
r.
iBG
P N
ext
Ho
pW
hen
a B
GP
rout
er r
ecei
ves
an u
pdat
e fr
om a
n eB
GP
neig
hbor
, it
mus
t pa
ss t
hat
upda
te t
o it
s iB
GP
neig
hbor
s w
itho
ut c
hang
ing
the
next
-hop
att
ribu
te. T
he n
ext-
hop
IP a
ddre
ss is
the
IP
addr
ess
of a
n ed
ge r
oute
r be
long
ing
to t
he n
ext-
hop
auto
nom
ous
AS
100
AS
300
AS
200
AS
400
10.1
.1.0
AS
100
AS
200
Rtr
A
Rtr
C
Rtr
D
Rtr
B
0910_BSCIssf.fm Page 250 Tuesday, September 9, 2003 8:24 AM
BGP 251
syst
em. T
here
fore
, iB
GP
rout
ers
mus
t ha
ve a
rou
te t
o th
e ne
twor
k co
nnec
ting
the
ir
auto
nom
ous
syst
em t
o th
at e
dge
rout
er. F
or e
xam
ple,
in t
he fi
gure
bel
ow, R
trA
sen
ds
an u
pdat
e to
Rtr
B, l
isti
ng a
nex
t ho
p of
10.
2.2.
1—it
’s se
rial
inte
rfac
e. W
hen
Rtr
B f
or-
war
ds t
hat
upda
te t
o R
trC
, the
nex
t-ho
p IP
add
ress
will
sti
ll be
10.
2.2.
1. R
trC
nee
ds
to h
ave
a ro
ute
to t
he 1
0.2.
2.0
netw
ork
to h
ave
a va
lid n
ext
hop.
BG
P N
ext
Ho
p o
n a
Mu
ltia
ccess N
etw
ork
On
a m
ulti
acce
ss n
etw
ork,
BG
P ca
n ad
just
the
nex
t-ho
p at
trib
ute
to a
void
an
extr
a ho
p. I
n th
e pr
evio
us fi
gure
, Rtr
C a
nd R
trD
are
eB
GP
peer
s, a
nd R
trC
is a
n iB
GP
peer
w
ith
Rtr
B. W
hen
C s
ends
an
upda
te to
D a
bout
net
wor
k 10
.2.2
.0, i
t nor
mal
ly g
ives
its
inte
rfac
e IP
add
ress
as
the
next
hop
for
D t
o us
e. B
ut s
ince
B, C
, and
D a
re a
ll on
the
sa
me
mul
tiac
cess
net
wor
k, it
add
s an
ext
ra h
op f
or D
to
send
tra
ffic
to C
, and
C t
o se
nd it
on
to B
. So
Rtr
C a
dver
tise
s a
next
hop
of
10.3
.3.3
(R
trB
’s in
terf
ace)
for
the
10
.2.2
.0 n
etw
ork.
To
chan
ge th
is b
ehav
ior,
use
the
neig
hbor
[ip
addr
ess]
nex
t-ho
p-se
lf
com
man
d.
BG
P S
yn
ch
ron
izati
on
Ru
leW
hen
a B
GP
rout
er r
ecei
ves
info
rmat
ion
abou
t a
netw
ork
from
an
iBG
P ne
ighb
or, i
t do
es n
ot u
se th
at in
form
atio
n un
til a
mat
chin
g ro
ute
is le
arne
d vi
a an
IGP
or s
tatic
rou
te.
It a
lso
does
not
adv
erti
se t
hat
rout
e to
an
eBG
P ne
ighb
or. I
n th
e pr
eced
ing
figur
e, if
R
trB
adv
erti
ses
a ro
ute
to R
trC
, C d
oes
not
subm
it it
to
the
rout
ing
tabl
e or
adv
erti
se
it to
Rtr
D u
nles
s it
als
o le
arns
the
rout
e fr
om s
ome
othe
r IG
P so
urce
. It i
s us
ually
saf
e to
tu
rn o
ff s
ynch
roni
zati
on w
hen
all r
oute
rs in
the
auto
nom
ous
syst
em a
re r
unni
ng B
GP.
To
turn
it o
ff, u
se t
he c
omm
and
no s
ynch
roni
zatio
n un
der
BG
P ro
uter
con
fig m
ode.
Basic
BG
P C
om
man
ds
AS
100
10.2
.2.1
AS
300
10.3
.3.1
AS
200
Rtr
AR
trD
Rtr
CR
trB10
.2.2
.2 10.3
.3.3
10.3
.3.2
Co
mm
an
dD
escri
pti
on
rout
er b
gp [
AS
num
ber]
Star
ts t
he B
GP
rout
ing
proc
ess
on t
he r
oute
r.
neig
hbor
[ip
add
ress
] re
mot
e-as
[A
S nu
mbe
r]Se
ts u
p a
peer
ing
betw
een
BG
P ro
uter
s.
neig
hbor
[pe
er g
roup
nam
e] p
eer-
grou
pC
reat
es a
pee
r gr
oup,
w
hich
you
can
the
n pu
t ne
ighb
ors
in.
neig
hbor
[ip
add
ress
] pe
er-g
roup
[pe
er g
roup
nam
e]A
ssig
ns a
nei
ghbo
r to
a
peer
gro
up.
neig
hbor
[ip
add
ress
] ne
xt-h
op-s
elf
Con
figur
es a
rou
ter
to
adve
rtis
e it
s co
nnec
ted
inte
rfac
e as
the
nex
t ho
p fo
r al
l rou
tes
to t
his
neig
hbor
.
neig
hbor
[ip
add
ress
] up
date
-sou
rce
loop
back
0C
onfig
ures
a r
oute
r to
use
th
e IP
add
ress
of
its
loop
back
0 in
terf
ace
as t
he
sour
ce f
or it
s ad
vert
isem
ents
to
this
ne
ighb
or.
no s
ynch
roni
zati
onTu
rns
off
BG
P sy
nchr
oniz
atio
n.
netw
ork
[pre
fix>
[m
ask
[sub
net
mas
k]]
Init
iate
s th
e ad
vert
isem
ent
of a
net
wor
k in
BG
P.
no a
uto-
sum
mar
yTu
rns
off
auto
mat
ic
sum
mar
izat
ion
of r
oute
s to
th
e cl
assf
ul n
etw
ork
boun
dary
.
0910_BSCIssf.fm Page 251 Tuesday, September 9, 2003 8:24 AM
252 BSCI Quick Reference SheetsT
he B
GP
netw
ork
Co
mm
an
dIn
mos
t IG
Ps, t
he n
etw
ork
com
man
d st
arts
the
rou
ting
pro
cess
on
an in
terf
ace.
In
BG
P, th
e co
mm
and
tells
the
rout
er to
ori
gina
te a
n ad
vert
isem
ent f
or th
at n
etw
ork.
The
ne
twor
k do
es n
ot h
ave
to b
e co
nnec
ted
to t
he r
oute
r; it
just
has
to
be in
the
rou
ting
ta
ble.
In
theo
ry, i
t co
uld
even
be
a ne
twor
k in
a d
iffe
rent
aut
onom
ous
syst
em (
not
usu-
ally
rec
omm
ende
d). W
hen
adve
rtis
ing
a ne
twor
k, B
GP
assu
mes
you
are
usi
ng t
he
defa
ult
clas
sful
sub
net
mas
k. I
f yo
u w
ant
to a
dver
tise
a s
ubne
t, y
ou m
ust
use
the
opti
onal
key
wor
d m
ask
and
spec
ify
the
subn
et m
ask
to u
se.
BG
P P
eeri
ng
BG
P as
sum
es t
hat
exte
rnal
nei
ghbo
rs a
re d
irec
tly
conn
ecte
d an
d th
at t
hey
are
peer
ing
wit
h th
e IP
add
ress
of
the
dire
ctly
con
nect
ed in
terf
ace
of t
heir
nei
ghbo
r. If
not
, you
m
ust
tell
BG
P to
look
mor
e th
an o
ne h
op a
way
for
its
neig
hbor
, wit
h th
e ne
ighb
or
[ip
addr
ess]
ebg
p-m
ulti
hop
[no.
of
hops
] co
mm
and.
You
mig
ht u
se t
his
com
man
d if
you
are
pee
ring
wit
h lo
opba
ck in
terf
ace
IP a
ddre
sses
. BG
P as
sum
es t
hat
inte
rnal
ne
ighb
ors
mig
ht n
ot b
e di
rect
ly c
onne
cted
, so
this
com
man
d is
not
nee
ded
wit
h iB
GP.
BG
P P
eeri
ng
Sta
tes
•Id
le—
No
peer
ing;
rou
ter
is lo
okin
g fo
r ne
ighb
or. I
dle
(adm
in)
mea
ns t
hat
the
neig
hbor
rel
atio
nshi
p ha
s be
en a
dmin
istr
ativ
ely
shut
dow
n.•
Con
nect
—T
CP
hand
shak
e co
mpl
eted
.•
Ope
nSen
t—A
n op
en m
essa
ge w
as s
ent
to t
ry t
o es
tabl
ish
the
peer
ing
(als
o ca
lled
Act
ive
stat
e).
•O
penC
onfir
m—
Rou
ter
has
rece
ived
a r
eply
to
the
open
mes
sage
.•
Est
ablis
hed—
Rou
ters
hav
e a
BG
P pe
erin
g se
ssio
n. T
his
is t
he d
esir
ed s
tate
.
Su
mm
ari
zin
g B
GP
Ro
ute
sY
ou c
an p
erfo
rm r
oute
sum
mar
izat
ion
in B
GP
in s
ever
al w
ays:
•L
eave
aut
o-su
mm
ariz
atio
n on
and
allo
w t
he r
oute
r to
adv
erti
se t
he d
efau
lt
clas
sful
rou
te.
•U
se t
he n
etw
ork
com
man
d al
ong
wit
h a
stat
ic r
oute
poi
ntin
g to
Nul
l0. I
n th
e fo
llow
ing
figur
e, A
S200
has
the
ent
ire
10.2
.0.0
sub
net.
Fir
st, c
onfig
ure
a st
atic
ro
ute
for
the
sum
mar
y, p
oint
ing
to N
ull0
(re
mem
ber
that
a r
oute
mus
t be
in
the
rout
ing
tabl
e be
fore
BG
P or
igin
ates
an
adve
rtis
emen
t fo
r th
at n
etw
ork)
:iiiipppp rrrroooouuuutttteeee 11110000....2222....0000....0000 222255555555....222255555555....0000....0000 nnnnuuuullllllll0000
The
n, p
ut a
net
wor
k st
atem
ent
for
the
sum
mar
y ne
twor
k in
to B
GP:
nnnneeeettttwwwwoooorrrrkkkk 11110000....2222....0000....0000 mmmmaaaasssskkkk 222255555555....222255555555....0000....0000
•U
se t
he a
ggre
gate
-add
ress
com
man
d—th
e pr
efer
red
met
hod.
At
leas
t on
e m
ore
spec
ific
netw
ork
of t
he s
umm
ariz
ed r
oute
s m
ust
be in
the
BG
P ta
ble,
eit
her
from
th
e ne
twor
k co
mm
and,
or
via
an a
dver
tise
men
t fr
om a
noth
er r
oute
r.In
the
fol
low
ing
figur
e, R
trB
use
s th
e fo
llow
ing
com
man
d to
sum
mar
ize
its
subn
ets:
aggregate-address 10.2.0.0 255.255.0.0
BG
P ad
vert
ises
the
sum
mar
y ro
ute
and
the
mor
e sp
ecifi
c ro
utes
. To
supp
ress
adv
erti
se-
men
t of
the
spe
cific
rou
tes,
add
the
sum
mar
y-on
ly k
eyw
ord
to t
he p
rece
ding
com
-m
and.
If
the
rout
es c
ome
from
oth
er a
uton
omou
s sy
stem
s, y
ou s
houl
d ad
d th
e as
-set
ke
ywor
d. T
his
tells
BG
P to
adv
erti
se a
list
of
the
auto
nom
ous
syst
em n
umbe
rs a
ssoc
i-at
ed w
ith
the
spec
ific
rout
es. B
GP’
s de
faul
t is
to
adve
rtis
e th
e ro
ute
wit
h on
ly t
he
auto
nom
ous
syst
em n
umbe
r of
the
sum
mar
izin
g ro
uter
. The
agg
rega
te-a
ddre
ss c
om-
man
d ca
uses
BG
P to
aut
omat
ical
ly c
reat
e a
rout
e fo
r th
e su
mm
ary,
poi
ntin
g to
Nul
l0,
to p
reve
nt lo
op f
orm
atio
n.
AS
100
AS
200
10.2
.0.0
10.2
.1.0
10.2
.3.0
… 10.2
.255
.0
Rtr
A
Rtr
B
0910_BSCIssf.fm Page 252 Tuesday, September 9, 2003 8:24 AM
BGP 253
BG
P A
ttri
bu
tes
BG
P ch
oose
s a
rout
e to
net
wor
k ba
sed
on t
he a
ttri
bute
s of
its
path
. Fou
r ca
tego
ries
of
attr
ibut
es e
xist
:•
Wel
l-kn
own
man
dato
ry—
Mus
t be
rec
ogni
zed
by a
ll B
GP
rout
ers,
pre
sent
in a
ll B
GP
upda
tes,
and
pas
sed
on t
o ot
her
BG
P ro
uter
s. E
xam
ple:
aut
onom
ous
syst
em
path
, ori
gin,
nex
t ho
p.•
Wel
l-kno
wn
disc
retio
nary
—M
ust b
e re
cogn
ized
by
all B
GP
rout
ers
and
pass
ed o
n to
ot
her
BG
P ro
uter
s, b
ut n
eed
not b
e pr
esen
t in
an u
pdat
e. E
xam
ple:
Loc
al p
refe
renc
e.•
Opt
iona
l tra
nsit
ive—
Mig
ht o
r m
ight
not
be
reco
gniz
ed b
y a
BG
P ro
uter
, but
is
pass
ed o
n to
oth
er B
GP
rout
ers.
If n
ot r
ecog
nize
d, it
is m
arke
d as
par
tial.
Exa
mpl
e:
aggr
egat
or, c
omm
unit
y.•
Opt
iona
l non
tran
siti
ve—
Mig
ht o
r m
ight
not
be
reco
gniz
ed b
y a
BG
P ro
uter
and
is
not
pas
sed
on t
o ot
her
rout
ers.
Exa
mpl
e: M
ulti
-Exi
t D
iscr
imin
ator
(M
ED
),
orig
inat
or I
D.
Ap
ply
ing
BG
P P
olicie
sT
hese
att
ribu
tes
are
usua
lly m
anip
ulat
ed u
sing
rou
te m
aps.
You
can
set
a d
efau
lt lo
cal
pref
eren
ce b
y us
ing
the
com
man
d bg
p de
faul
t lo
cal-
pref
eren
ce a
nd a
def
ault
ME
D f
or
redi
stri
bute
d ro
utes
wit
h th
e de
faul
t-m
etri
c co
mm
and
unde
r th
e B
GP
rout
ing
proc
ess.
But
by
usin
g ro
ute
map
s, y
ou c
an c
hang
e at
trib
utes
for
cer
tain
nei
ghbo
rs o
nly,
or
for
cert
ain
rout
es o
nly.
Whe
n at
trib
utes
are
cha
nged
, you
mus
t te
ll B
GP
to a
pply
the
cha
nges
. Eit
her
clea
r th
e B
GP
sess
ion
(cle
ar ip
bgp
* )
or
do a
sof
t re
set
(cle
ar ip
bgp
* s
oft
in |
out)
.
BG
P P
ath
Sele
cti
on
Cri
teri
aB
GP
trie
s to
nar
row
its
path
sel
ecti
on d
own
to o
ne b
est
path
; it
does
not
load
bal
ance
by
def
ault
. To
do s
o, it
exa
min
es t
he p
ath
attr
ibut
es in
the
fol
low
ing
orde
r:1.
Is t
he r
oute
syn
chro
nize
d (i
f iB
GP)
wit
h a
valid
nex
t ho
p an
d no
aut
onom
ous
syst
em lo
ops?
2.C
hoos
e th
e ro
ute
wit
h th
e hi
ghes
t w
eigh
t.3.
If w
eigh
t is
not
set
, cho
ose
the
rout
e w
ith
the
high
est
loca
l pre
fere
nce.
4.C
hoos
e a
rout
e th
at w
as o
rigi
nate
d lo
cally
ove
r on
e th
at w
as a
dver
tise
d to
you
.5.
Cho
ose
the
path
wit
h th
e sh
orte
st a
uton
omou
s sy
stem
pat
h.6.
Cho
ose
the
path
wit
h th
e lo
wes
t or
igin
cod
e (i
is lo
wes
t, e
is n
ext,
? is
last
).7.
Cho
ose
the
rout
e w
ith th
e lo
wes
t ME
D, i
f the
sam
e au
tono
mou
s sy
stem
adv
ertis
es
the
poss
ible
rou
tes.
8.C
hoos
e an
eB
GP
rout
e ov
er a
n iB
GP
rout
e.9.
Cho
ose
the
rout
e th
roug
h th
e ne
ares
t IG
P ne
ighb
or.
10.
Cho
ose
the
olde
st r
oute
.11
.C
hoos
e a
path
thr
ough
the
nei
ghbo
r w
ith
the
low
est
rout
er I
D.
To e
nabl
e B
GP
to lo
ad b
alan
ce o
ver
mor
e th
an o
ne p
ath,
you
mus
t ent
er th
e co
mm
and
max
imum
-pat
hs [
no. o
f pa
ths]
. BG
P ca
n lo
ad b
alan
ce o
ver
a m
axim
um o
f 6
path
s.
Mu
ltih
om
ing
Mul
tiho
min
g m
eans
con
nect
ing
to m
ore
than
one
ISP
at
the
sam
e ti
me.
Mul
tiho
min
g is
don
e fo
r re
dund
ancy
and
bac
kup
in c
ase
one
ISP
fails
—an
d fo
r be
tter
pe
rfor
man
ce—
if o
ne I
SP p
rovi
des
a be
tter
pat
h to
oft
en u
sed
netw
orks
. Thr
ee w
ays
exis
t to
rec
eive
rou
tes
from
eac
h IS
P:•
Def
ault
rou
tes
from
eac
h pr
ovid
er. L
ow u
se o
f ba
ndw
idth
and
rou
ter
reso
urce
s,
IGP
met
ric
dete
rmin
es p
ath
chos
en f
or r
oute
s ou
tsid
e th
e au
tono
mou
s sy
stem
.•
Def
ault
rou
tes
plus
som
e m
ore
spec
ific
rout
es. M
ediu
m u
se o
f ba
ndw
idth
and
ro
uter
res
ourc
es. C
an m
anip
ulat
e pa
th f
or s
peci
fic r
oute
s, I
GP
met
ric
choo
ses
path
for
def
ault
rou
tes.
•A
ll ro
utes
fro
m a
ll pr
ovid
ers.
Hig
hest
use
of
band
wid
th a
nd r
oute
r re
sour
ces.
Ty
pica
lly d
one
only
by
ISPs
. Pat
h se
lect
ion
can
be c
ontr
olle
d vi
a B
GP
polic
y ro
utin
g to
ols.
Aut
onom
ous
syst
em p
ath
An
orde
red
list
of a
ll th
e au
tono
mou
s sy
stem
s th
roug
h w
hich
thi
s up
date
has
pas
sed.
Ori
gin
How
BG
P le
arne
d of
thi
s ne
twor
k. i
= by
net
wor
k co
mm
and,
e =
from
EG
P, ?
= r
edis
trib
uted
from
oth
er
sour
ce.
Nex
t ho
pT
he I
P ad
dres
s of
the
nex
t-ho
p ro
uter
.
Loc
al p
refe
renc
eA
val
ue t
ellin
g iB
GP
peer
s w
hich
pat
h to
sel
ect
for
traf
fic le
avin
g th
e A
S.
Wei
ght
Cis
co p
ropr
ieta
ry, t
o te
ll a
rout
er w
hich
of
mul
tipl
e lo
cal p
aths
to
sele
ct f
or t
raffi
c le
avin
g th
e A
S. O
nly
has
loca
l sig
nific
ant.
Mul
ti-E
xit
Dis
crim
inat
or
(ME
D)
Sugg
ests
to
a ne
ighb
or a
uton
omou
s sy
stem
whi
ch o
f m
ulti
ple
path
s to
sel
ect
for
traf
fic b
ound
for
you
r au
tono
mou
s sy
stem
.
0910_BSCIssf.fm Page 253 Tuesday, September 9, 2003 8:24 AM
