Post on 28-Feb-2018
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1Version 3.1
Module 9Basic Router
Troubleshooting
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2Version 3.1
The Routing Table and show ip route
Command
Routers build routing tables to:
list available routes for forwarding data
select the best path to a destination
show ip routedisplays routing table information aboutall known networks and subnetworks
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3Version 3.1
Example Routing Table
When RT recei!es a pac"et destined #or 19$.1%&.'.'%(
it loo"s #or the pre#ix 19$.1%&.'.)*$' in its table.
RT then #or+ards the pac"et out an inter#ace,Ethernet)- based on the routing table entr.
/# RT recei!es a pac"et destined #or 1).3.$1.0( it sends
that pac"et out erial )
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4Version 3.1
Example Routing Table
' routes 2 directl connected
The router +ill drop an pac"et destined #or a net+or"
not listed in the routing table
o +hat do ou do +ith those pac"ets that this router
doesnt ha!e a route to4
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5Version 3.1
dding Routes
tatic routing
Manuall entered b the administrator5
more secure
lo+ processor o!erhead ha!e precise control o# path selection
6namic routing
router learns route #rom other routers( dnamicall
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6Version 3.1
7ate+a o# 8ast Resort
,6e#ault tatic Route-
T+o +as to staticall con#igure de#ault
routes5
rom global con#iguration mode
ip route 0.0.0.0 0.0.0.0 [next-hop
interface|exit-interface]
rom router con#iguration mode
ip default network [network number]
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7/237Version 3.1
ip default-network
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8/238Version 3.1
ip route
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Version 3.1
Routing :rocesses
Remember that the /: source and destination do notchange in the pac"et( but the MC addresses do
change.
The pac"et is #or+arded based on the MC address o#
the next hop.
8aer 3 address is al+as used in routing( but the
MC address has to change because the data is
#ramed as it mo!es out on the data lin" laer.
ource to destination ;;; +e are al+as tal"ing about
net+or" addressing
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Version 3.1
Route Metrics
Routing protocols use metrics to determine the best
route to a destination.
The metric is a !alue that measures the desirabilit o#
a route. The smaller the metric number( the better the path.
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Version 3.1
M
E
T
R
I
C
S
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Version 3.1
Route Metrics
The more #actors that ma"e up a metric( the greater the#lexibilit to tailor net+or" operations to meet speci#icneeds.
B de#ault( /7R: uses the static #actors band+idth and
dela to calculate a metric !alue ,so band+idth and delacan actuall be entered b the administrator-.
/7R: ma also be con#igured to include the dnamic#actors( load and reliabilit( in the metric calculation.
Remember( /7R: uses the metric
Metric < band+idth = dela
Be sure to do the Interactive Media Activity in 9.1.6
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Version 3.1
Troubleshooting
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Version 3.1
Testing b >/ 8aers
8aer 1 2 chec" ob!ious #irst ,lights on a ?/C-
Bro"en cables
6isconnected cables
Cables connected to the +rong ports
/ntermittent cable connection
Wrong cables used #or the tas" at hand ,must userollo!ers( crosso!er cables( and straight;throughcables correctl-
Transcei!er problems 6CE cable problems
6TE cable problems
6e!ices turned o##
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15Version 3.1
Testing b >/ 8aers
8aer $ errors5
/mproperl con#igured serial inter#aces
/mproperl con#igured Ethernet inter#aces
/mproper encapsulation set ,@68C is de#ault #orserial inter#aces-
/mproper cloc"rate settings on serial inter#aces
?et+or" inter#ace card ,?/C- problems
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16Version 3.1
Testing b >/ 8aers
8aer 3 errors5
Routing protocol not enabled
Wrong routing protocol enabled
/ncorrect /: addresses /ncorrect subnet mas"s
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17Version 3.1
pingAtilit ,8aer 3 testing-
Mabe the host isnt a!ailable
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18Version 3.1
Telnet application ,8aer testing-
Actually verifies all seven layers of the OSI
If telnet is not working then that means that there are
upper!layer application layer problems"
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19Version 3.1
show interfaces serial
#sed to discover $ayer % & $ayer ' problems with the
router
(hen the line is down the protocol is always down
because there is no useable media for the $ayer ' protocol"If the interface is up and the line protocol is down a $ayer '
problem e)ists *no keepalives no clock rate encap different+
,ou would never see serial -.- is down line protocol is up
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20Version 3.1
show interfaces serial
Interpreting theShow Interfaces SerialCommand
One of the most important elements of theshow
interfaces serialcommand output is the display of the
line and data link protocol status.
The line status is triggered by a Carrier Detect signal, and
refers to the physical layer status. However, the line protocol,
triggered bykeepaliveframes, refers to the data link framing.
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21Version 3.1
show interfaces serial
no+ all
o# theseD
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22Version 3.1
show ip protocols
/he show ip protocolscommand shows the following:
Sources of routing updates
/he networks being advertised
#pdate timer values 0)" If a network is not being included in the routing
updates and should be an administrator could issue
this command to see which networks are being
advertised
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debug
1e 2areful333
4ebug will give you live changing information"
/herefore it will use processor time that may disrupt
normal router operation
0specially should not use 5debug all6 but be more
specific like
debug ip rip *only live info on rip routing ip+
/o turn off debug use undebug all or u all