Cn Chp4 [Compatibility Mode]

8/9/2019 Cn Chp4 [Compatibility Mode]

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Computer NetworksComputer Networks

[email protected]@iust.ac.ir Network LayerNetwork Layer [email protected] IUST-Network Layer

Network Layer


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Chapter 4: Network LayerChapter 4: Network Layer

Chapter goals: understanding principles

behind network layerservices: routing (path selection)

dealing with scale

Overview: network layer services

routing principles: pathselection

hierarchical routing


how a router works advanced topics: IPv6,

mobility

instantiation and

implementation in theInternet

Internet routing protocolsreliable transfer intra-domain

inter-domain

whats inside a router?

IPv6

mobility


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Chapter 4 OutlineChapter 4 Outline

4.1 Introduction and Network Service Models

4.2 Routing Principles4.3 Hierarchical Routing

4.4 The Internet (IP) Protocol


4.5 Routing in the Internet4.6 Whats Inside a Router

4.7 IPv6

4.8 Multicast Routing

4.9 Mobility


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Network Layer FunctionsNetwork Layer Functions

transport packet fromsending to receiving hosts

network layer protocols ineveryhost, router

three important functions:

applicationtransportnetworkdata linkphysical

networkdata linkphysical

networkdata link

physical

networkdata link




taken by packets from sourceto dest. (Routing Algorithms)

forwarding:move packetsfrom routers input to

appropriate router output call setup:some network

architectures require routercall setup along path before

data flows



p ysica


applicationtransportnetworkdata linkphysical


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Network Service ModelNetwork Service Model

Q: What service modelforchannel transportingpackets from sender toreceiver?

The most importantabstraction provided

by network layer:


guaranteed bandwidth? preservation of inter-packet

timing (no jitter)? loss-free delivery? in-order delivery? congestion feedback to

sender?

virtual circuitor

datagram?


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Virtual circuitsVirtual circuits

source-to-destination path behaves much liketelephone circuit

performance-wise

network actions along source-to-destination path


call setup, teardown for each call beforedata can flow each packet carries VC identifier (not destination host ID)

everyrouter on source-destination path maintains statefor each passing connection transport-layer connection only involved two end systems

Link and router resources (bandwidth, buffers) may beallocatedto VC to get circuit-like performance.


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Virtual Circuits: Signaling ProtocolsVirtual Circuits: Signaling Protocols

used to setup, maintain teardown VC

used in ATM, frame-relay, X.25 not used in todays Internet

6. Receive data

application


1. Initiate call

2. Incoming call

4. Call connected5. Data flow begins

application

transportnetworkdata linkphysical



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Datagram networks:Datagram networks: the Internet modelthe Internet model

2. Receive Data application

no call setup at network layer

routers: no state about end-to-end connections no network-level concept of connection

packets forwarded using destination host address packets between same source-destination

pair may take different paths


1. Send Data

application




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Network Layer Service Models:Network Layer Service Models:

NetworkArchitecture

Internet

ATM

ServiceModel

best effort

CBR

Bandwidth

none

constantrate

Loss

no

yes

Order

no

yes

Timing

no

yes

Congestionfeedback

no (inferredvia loss)nocongestion

Guarantees ?

e

e

te

rate


Internet model being extended: Integrated services,Differentiated Services

Chapter 6

ATM

ATM

ATM

VBR

ABR

UBR

guaranteedrateguaranteedminimumnone

yes

no

no

yes

yes

yes

yes

no

no

nocongestionyes

noCBR:Constantbit

ra

VBR:Variablebitrat

ABR:Availablebit

ra

UBR:Unspecified

bit


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QoS FactorsQoS Factors

Timing

Connection Establishment Delay

End-To-End Delay Connection Establishment Failure Probability

Throughput or Bandwidth Guarantee


Ordering Preservation Congestion Indication (Control)

Bit-Error rate or Packet-Loss Rate Control

Protection Priority

Resilience (Return Back to Normal Operation).


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Service ClasesService Clases

Guaranteed Quality of Service

Predictive Quality of Service


es or ua y o erv ce


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Guaranteed QoSGuaranteed QoS

Specified through QoS parameter values deterministic

statistical

Single value - average (threshold, target)

Pair of values - interval


Triple of values max., mean, min.


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Predictable ServicePredictable Service

Parameter bounds based on history, that is, past

network behavior. Parameter values are measured, and certain

statistical analyses may be carried out



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Best Effort ServicesBest Effort Services

No guarantees of quality, no QoS parameter values UDP/IP

Partial guarantees, some QoS parameter values


re g ven. TCP/IP


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Datagram or VC Network: why?Datagram or VC Network: why?

Internet data exchange among

computers elastic service, no strict

timing req. smart end systems

(computers)

ATM evolved from telephony human conversation:

strict timing, reliabilityrequirements

need for guaranteedservice


can adapt, performcontrol, error recovery simple inside network,

complexity at edge many link types

different characteristics uniform service is

difficult

dumb end systems telephones complexity inside

network


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Active Queue Management (AQM)Active Queue Management (AQM)

Performance Degradation in current TCPCongestion Control Multiple packet loss

Low link utilization

Congestion colla se


The role of the router (i.e., network) Control congestion effectively with a network

Allocate bandwidth fairly


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FIFO Queueing in the RouterFIFO Queueing in the Router

(Drop Tail)(Drop Tail)

Network


Single queue maintained

n er ace


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Network



Dequeue from head

n er ace


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Network



Dequeue from head Enqueue at tail

n er ace


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Network



Dequeue from head Enqueue at tailWhen full

n er ace


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Network



Dequeue from head Enqueue at tailWhen full drop arriving packet (drop-tail)

n er ace


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Active Queue ManagementActive Queue Management

Goals:

Better congestion notification for responsive flows(i.e. TCP)


Maintain shorter queues

Fairness in drops (proportional)


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RED OperationRED Operation



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Max Queue Size

Active Queue ManagementActive Queue Management

Random Early Detection (RED)Random Early Detection (RED)

Forced drop

Drop probability

Average queue length


Time

ax res o

Min Threshold

Probabilistic drops

No drops


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4.2 Routing Principles Link state routing Distance vector routing

4.3 Hierarchical Routing


4.4 The Internet (IP) Protocol4.5 Routing in the Internet

4.6 Whats Inside a Router

4.7 IPv64.8 Multicast Routing

4.9 Mobility


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RoutingRouting

Gra h abstraction for

Goal: determine good path

(sequence of routers) thrunetwork from source to dest.

A F

CB

12

2

5

35

3

Routing protocol


routing algorithms: graph nodes are

routers

graph edges arephysical links link cost: delay, $ cost,

or congestion level

good path: typically means minimum

cost path

other definitions possible

D E1

2

Abstract model of a network


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Routing Algorithm ClassificationsRouting Algorithm Classifications

1. Global: all routers have complete

topology, link cost info link state algorithms

1. Static:

routes update slowly

over time

2. D namic:


. router knows physically-

connected neighbors, linkcosts to neighbors

iterative process ofcomputation, exchange ofinfo with neighbors

distance vector algorithms

routes update morequickly

periodic update

in response to linkcost changes


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A LinkA Link--State Routing AlgorithmState Routing Algorithm

Dijkstras algorithm (global) net topology, link costs known to all

nodes accomplished via link state

broadcast


ll nodes have same information computes least cost paths from one

node (source) to all other nodes

gives routing table for that node iterative: after k iterations, know least

cost path to k destinations.


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Notation:Notation:

N: set of nodes whoseleast cost path

definitively knownc(i,j): link cost from node

i toj. cost infinite if

A F

D

C

E

B

1

1

2

2

2

53

5

3

5

3


not direct neighbors p(v): nodes along path

from source to v

D(v): current value ofcost of path fromsource to destinationv.

N: A, B, C, D, E, F

C(A,C)=5; C(C,A)=5C(B,D)=2; C(D,B)=3

Source=Ap(F): A-D-E-FD(F)=4

Example:


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1 Initialization:2 N = {A}

3 for all nodes v4 if v adjacent to A5 then D(v) = c(A,v)6 else D(v) = infinity

Dijsktras AlgorithmDijsktras Algorithm

v

w

D(v) c(w,v)

A

fnodes(exceptthesource)


8 Loop9 find w not in N such that D(w) is a minimum10 add w to N11 update D(v) for all v adjacent to w and not in N:

12 D(v) = min( D(v), D(w) + c(w,v) )13 /* new cost to v is either old cost to v or known14 shortest path cost to w plus cost from w to v */15 untilall nodes in N

w

n(n+1)/2)

times

n=numbe

ro


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Dijkstras Algorithm: exampleDijkstras Algorithm: example

computes least cost paths from node A to all other nodes

Step

0123

start N

AADADE

ADEB

D(B),p(B)

2,A-B2,A-B2,A-B2,A-B

D(C),p(C)

5,A-C4,A-D-C3,A-D-E-C3,A-D-E-C

D(D),p(D)

1,A-D1,A-D1,A-D1,A-D

D(E),p(E)

infinity2,A-D-E2,A-D-E2,A-D-E

D(F),p(F)

infinityinfinity4,A-D-E-F4,A-D-E-F


5 ADEBCFADEBCF, -

2,A-B3,A-D-E-C3,A-D-E-C

1,A-

1,A-D

, - -

2,A-D-E4,A-D-E-F4,A-D-E-F

A F

D

C

E

B

1

1

1

2

2

2

53

53

D(v): Distance (cost) of A to v.

P(v): nodes along path fromA to v.


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Dijkstras Algorithm: discussion1Dijkstras Algorithm: discussion1

Algorithm complexity: Suppose there are nnodes, except source

First iteration: Search through all nnodes to determine the node,w, not in Nthat has the minimum cost.

Second iteration: Check n- 1 nodes to determine minimum cost.

Third iteration: n- 2 nodes, and so on.


Total number of nodes searched: n(n+ 1)/2 The implementation of the link state algorithm has worst-case

complexity of order nsquared: O(n2).

A more sophisticated implementation of this algorithm, using adata structure known as a heap, can find the minimum in line 9 inlogarithmic rather than linear time, thus reducing the complexity:O( nlog(n) )


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D B

A

0

1

1

1+e

e0 0


Oscillations possibility: Suppose link costs are equal to

the load carried on the link, orthe delay that experienced.

Link costs are not symmetric,


e

1

Fig. a- Initial routing

c(A,B) equals c(B,A) only if theload on both directions on theABlink is the same.

Nodes B and Doriginates a unit

of traffic destined for A. Node Coriginates eunit forA.

Discussion2 (cont )Discussion2 (cont )


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oscillations possible: Algorithm is run: C

determines (Fig. a) the

clockwise path to Ahas a costof 1, while thecounterclockwise path to A

Discussion2 (cont.)Discussion2 (cont.)

D

C

B

A

0

1

1

1+e

e

e

1

0 0

Fig. a- Initial routing


.

least-cost path to Ais nowclockwise. Similarly, Bdetermines that

its new least-cost path to Ais

also clockwise, resulting incosts shown in Fig. b.

D

C

B

A

1+e

00

0

1

2+e

Fig. b- B, C find betterpath to A is clockwise

1e

1

Discussion2 (cont )Discussion2 (cont )


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oscillations possible:

When algorithm is run next,nodes B, C, and Dall detect azero-cost ath to Ain the

Discussion2 (cont.)Discussion2 (cont.)

Fi . c- B, C, D find better

D

C

B

A

01+e1

2+e

0

0

11

e


counterclockwise direction,and all route their traffic tothe counterclockwise routes.

The next time the LSalgorithm is run, B, C, and Dallthen route their traffic to theclockwise routes.

D

C

B

A

1+e00

0

1

2+e

11

e

path to A is counterclockwise

Fig. d- B, C, D find better

path to A is clockwise


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To prevent such oscillations: Solution1 :link costs not depend on the amount of traffic carried ,an

unacceptable solution since one goal of routing is to avoid highly congested(for example, high-delay) links.

Solution2 :all routers do not run the LS algorithm at the same time(a reasonable solution). Routers run the LS al orithm with the same eriodicit the



execution instance of the algorithm would not be the same ateach node.

Researchers have noted: Routers in the Internet can self-synchronize among themselves. That is, even though theyinitially execute the algorithm with the same period but atdifferent instants of time, the algorithm execution instance caneventually become, and remain, synchronized at the routers.

Avoid such self-synchronization: Introduce randomization intothe period between execution instants of the algorithm at eachnode.

Distance Vector Routing AlgorithmDistance Vector Routing Algorithm


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Distance Vector Routing AlgorithmDistance Vector Routing Algorithm(Decentralized)(Decentralized)

Iterative: continues until no

nodes exchange info. self-terminating: no

signal to stop

Distance Table data structure each node has its own:

row for each possible destination

column for each directly-attached neighbor to node


nodes need notexchange info/iteratein lock step!

distributed: each node

communicates onlywithdirectly-attachedneighbors

example: in node X, for dest. Yvia neighbor Z: DX(Y,Z)

distance fromX toY, viaZ as next hop

D (Y,Z)X

c(X,Z) + min {D (Y,w)}Z

w

=

Di t T bl lDi t T bl l


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Distance Table: exampleDistance Table: example

2

D

CB

A

E1

7

1

8

2source

ABCD

A

17

64

B

1489

11

D

55

4

neighbor: j

estination

:i


B

w=

c(E,B) + min {D (A,w)}=

8 + 6 = 14

E

D (A,B)=E

B

D (A,C)B

D

C

c(E,B)

Bs neighbor

D(i, j)EDistance table:

Di t t bl i ti t blDi t t bl i ti t bl


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Distance table gives routing tableDistance table gives routing table

D ()

A

A

1

B

14

D

5

E

cost to destination via

A A,1

Outgoing linkto use, costD ()

E


C

D

6

4

9

11

4

2

C

D

,

D,4

D,4

Distance table Routing tableof node E

Di t V t R ti iDi t V t R ti i


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Distance Vector Routing: overviewDistance Vector Routing: overview

Iterative, asynchronous:each local iteration causedby:

local link cost change

message from neighbor: itsleast cost path change

waitfor (change in local linkcost or message fromneighbor)

Each node:


from neighbor

Distributed: each node notifies

neighbors onlywhen its

least cost path to anydestination changes neighbors then notify

their neighbors ifnecessary

recomputedistance table

if least cost path to any

destination has changed,

notifyneighbors

Distance Vector Algorithm:Distance Vector Algorithm:


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Distance Vector Algorithm:Distance Vector Algorithm:

1 Initialization:

2 for all adjacent nodes v:

At node: X

X

v

*

DX (*,v)

Xs adjacentsdestinations

w

Y

DX (y,w)


,v = t e means or a esst nat ons

4 DX (v,v) = c(X,v)

5 for all destinations, y6 send minW DX (y,w) to each neighbor /* w over allX's neighbors */

Distance Vector Algorithm (cont ):Distance Vector Algorithm (cont ):


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Distance Vector Algorithm (cont.):Distance Vector Algorithm (cont.):8 loop

9 wait ( until I see a link cost change to neighbor v10 or until I receive update from neighbor v )1112 if ( c(X,v) changes by d )

13 /* change cost to all dest's via neighbor v by d */14 /* note: d could be positive or negative */15 for all destinations y: DX (y,v) = DX (y,v) + d16


e se i up ate receive rom v or estination

18 /* shortest path from V to some Y has changed */19 /* V has sent a new value for its minW DV (Y,w) */20 /* call this received new value is "newval" */21 for the single destination y: DX (Y,v) = c(X,v) + newval

2223 if we have a new minW DX(Y,w) for any destination Y24 send new value of minW DX(Y,w) to all neighbors25

26 forever

Distance Vector Algorithm: exampleDistance Vector Algorithm: example


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2Y

1

Node Xs table

Node Ys table


X Z7

Node Zs table

time

new minimum



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2

Y

X Z

1

7X learns this term from Y

X sends newDX(Y,Z) to Y and Z

X dose not sendsDX(Y,Y) to Y and Z.

1

2 2

3

4

4


D (Y,Z)X c(X,Z) + min {D (Y,w)}w=

= 7+1 = 8

Z

D (Z,Y)X c(X,Y) + min {D (Z,w)}w=

= 2+1 = 3

Y

X learns this term from Z

1

1


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Distance Vector: link cost changesDistance Vector: link cost changes


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Distance Vector: link cost changesDistance Vector: link cost changes

Link cost changes: Routing loop: in order to

get to X, Y routes through

Z, and Z routes through Y. count to infinity problem!

4Y

X Z

1

50

60


algorithmcontinues

on!

Poisoned reverse solution: count to infinity problem!Poisoned reverse solution: count to infinity problem!


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y py p

If Z routes through Y to get to X : Z tells Y its (Zs) distance to X is

infinite (so Y wont route to X via Z)

will this completely solve count toinfinity problem?

4Y

X Z

1

50

60


terminates

Comparison of LS and DV algorithmsComparison of LS and DV algorithms


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Co p so o S d go t sCo p so o S d go t s

Message complexity LS: with n nodes, E links,

O(nE) msgs sent each

DV: exchange between

neighbors only convergence time varies

S eed of Conver ence

Robustness: what happensif router malfunctions?

LS: Node (router) can

advertise incorrect linkcost

each node computes only


LS: O(n2

) algorithm requiresO(nE) msgs

may have oscillations

DV: convergence time varies

may be routing loops count-to-infinity problem

s own a e: ro us ness

DV: DV node can advertise

incorrect least-costpaths

each nodes table used byothers error propagate thru

network



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4.2 Routing Principles




4.5 Routing in the Internet4.6 Whats Inside a Router

4.7 IPv6

4.8 Multicast Routing4.9 Mobility

Hierarchical RoutingHierarchical Routing


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Hierarchical RoutingHierarchical Routing

The routing study thus far was idealized

all routers identical

network flat

nottrue in practice


scale: with 200 milliondestinations (hosts): cant store all dests in routing

tables (memory limitation)! routing table exchange would

leave no bandwidth left forsending data packets!

DV algorithm that iteratedamong large number ofrouters never converge!

administrativeautonomy: internet = network of

networks

each network admin maywant to control routing in itsown network


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IntraIntra--AS and InterAS and Inter--AS routingAS routing


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IntraIntra AS and InterAS and Inter AS routingAS routing

Gateways:perform inter-ASrouting amongstthemselves

perform intra-ASrouters with otherrouters in theirAS

C

A

B

C.b

A.a

A.c

B.a

a b

ad

bc

ac

b


Inter/intra-ASrouting in

gateway A.c

Routers in an AShave informationabout routing pathswithin that AS.

IntraIntra--ASASRoutingRouting

AlgorithmAlgorithm

InterInter--ASASRoutingRouting

AlgorithmAlgorithm

Routing TableRouting Table

DLDL DLDL DLDL

PHLPHLPHLPHL PHL To/from B.a and A.aTo/from A.b

To/from A.d

IntraIntra--AS and InterAS and Inter--AS routingAS routing


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Host2

ab

ac

b

C.b

A.a

B.a

A.c


A

Intra-AS routingwithin AS A

Intra-AS routingwithin AS B

Host1

db

c

Chapter 4 outlineChapter 4 outline


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pp

4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing

4.4 The Internet (IP) Protocol 4.4.1 IPv4 addressing 4.4.2 Moving a datagram from source to destination 4.4.3 Data ra or at


4.4.4 IP fragmentation 4.4.5 ICMP: Internet Control Message Protocol 4.4.6 DHCP: Dynamic Host Configuration Protocol 4.4.7 NAT: Network Address Translation

4.5 Routing in the Internet

4.6 Whats Inside a Router4.7 IPv64.8 Multicast Routing4.9 Mobility

The Internet Network layerThe Internet Network layer


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yy

Host, Router network-layer-functions:

Routing protocolspath selectionRIP, OSPF, BGP

IP protocoladdressing conventionsdatagram formatpacket handling conventions

Transport layer: TCP, UDP

orklayer


forwardingtable ICMP protocolerror reporting

router signaling

Link layer

physical layer

N

et

ICMP: Internet Control Message Protocol, RFC792

Internet Routing ProtocolInternet Routing Protocol


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gg

Intra-AS: administrator responsible for choice ofrouting algorithm within network Also known as Interior Gateway Protocols (IGP)

Most common Intra-AS routing protocols:RIP: Routing Information Protocol (RFCs1058,2453)

It is a distance vector protocol.


. .

OSPF: Open Shortest Path First (RFC2328) (Open Spec.)IGRP: Interior Gateway Routing Protocol (Cisco proprietary)

These are link-state protocol that uses flooding of link information and a

Dijkstra least-cost path algorithm.

Inter-AS: unique standard for inter-AS routing:BGP (RFC1771)

IP Addressing: IntroductionIP Addressing: Introduction


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IP address: 32-bitidentifier for host,router interface

interface:connectionbetween host/router

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.27


routers typically have

multiple interfaces

host may have multipleinterfaces

IP addressesassociated with eachinterface

223.1.3.2223.1.3.1

223.1.1.1 = 11011111 00000001 00000001 00000001

223 1 11

IP AddressingIP Addressing


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IP address: network part (high

order bits)

host part (low orderbits)

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.27


(from IP addressperspective) device interfaces with

same network part of

IP address can physically reach

each other withoutintervening router

223.1.3.2223.1.3.1

network consisting of 3 IP networks

LAN

IP AddressingIP Addressing223.1.1.2


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IP AddressingIP Addressing

How to find thenetworks?

Detach eachinterface fromrouter, host

223.1.1.1

223.1.1.3

223.1.1.4

223.1.7.0223.1.9.2


crea e s an s o

isolated networks

223.1.2.2223.1.2.1

223.1.2.6

223.1.3.2223.1.3.1

223.1.3.27

223.1.7.1

223.1.8.0223.1.8.1

223.1.9.1

Interconnectedsystem consistingof six networks.

Getting a datagram from source to dest.Getting a datagram from source to dest.


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IP datagram:miscields

sourceIP addr

destIP addr data

Dest. Net. Next Router Nhops

223.1.1 1

223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2

forwarding table in A


datagram remainsunchanged, as it travelssource to destination

addr fields of interest

here

. . .

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27 EB



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Starting at A, send IPdatagram addressed to B:

look u net. address of B in


223.1.1 1

223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2

miscfields 223.1.1.1 223.1.1.3 data



. . .

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27 EB

forwarding table

find B is on same net. as A

link layer will send datagramdirectly to B inside link-layerframe

B and A are directlyconnected



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223.1.1 1

223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2Starting at A, dest. E: look up network address of E

in forwarding table




E on differentnetwork

A, E not directly attached routing table: next hop

router to E is 223.1.1.4

link layer sends datagram torouter 223.1.1.4 inside link-layer frame

datagram arrives at 223.1.1.4

continued..

. . .

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27 EB



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Arriving at 223.1.4,destined for 223.1.2.2

look u network address of E


Dest. Net Router Nhops Interface

223.1.1 - 1 223.1.1.4

223.1.2 - 1 223.1.2.9223.1.3 - 1 223.1.3.27

forwarding table in router


. . .

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27 EB

in routers forwarding table

E on samenetwork as routersinterface 223.1.2.9

router, E directly attached

link layer sends datagram to223.1.2.2 inside link-layerframe via interface 223.1.2.9

datagram arrives at 223.1.2.2


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IP Addresses: ClassIP Addresses: Class--fullfull


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given notion of network, lets re-examine IP addresses:

class-full addressing:

0 network hostA

class1.0.0.0 to127.255.255.255

format range


110 network host

10 network hostB

C

D

128.0.0.0 to191.255.255.255

192.0.0.0 to223.255.255.255

224.0.0.0 to

239.255.255.255

32 bits

1110 multicast address

E 240.0.0.0 to255.255.255.2551111 reserved

ClassClass--full Summaryfull Summary


67/200

Address

ClassApplication

Number of

Network

Bits

Number of

Host Bits

Decimal

Address

Ran e

Number of

Networks

Number of

Possible

Host

Class A

Large

Networks 8 bits 24 bits 1 - 126 126 16,777,214

Class BMedium-

sized16 bits 16 bits 128 - 191 65,534 65,534

Class CSmall

24 bits 8 bits 192 - 223 2,097,152 254

The Class System


Class D and E

12.5%

Class C

12.5% Class A50%

Class B

25%

e wor s

Address depletionAddress depletion


68/200

In 1991 IAB identified 3 dangers Running out of class B addresses

Increase in nets has resulted in routing table explosion Increase in net/hosts exhausting 32 bit address space


Creative address space allocation {RFC 2050} Private addresses {RFC 1918}, Network Address

Translation (NAT) {RFC 1631}

Classless InterDomain Routing (CIDR) {RFC 1519}

IP version 6 (IPv6) {RFC 1883}

Creative IP address allocationCreative IP address allocation


69/200

Class A addresses 64 127 reserved Handle on individual basis

Class B only assigned given a demonstrated need Class C

divided u into 8 blocks allocated to re ional authorities


208-223 remains unassigned and unallocated

Three main registries handle assignments APNIC Asia & Pacific www.apnic.net ARIN N. & S. America, Caribbean & sub-Saharan Africa

www.arin.net RIPE Europe and surrounding areas www.ripe.net

Private IP AddressesPrivate IP Addresses


70/200

IP addresses that are not globally unique, but usedexclusively in an organization

Three ranges: 10.0.0.0 - 10.255.255.255 a single class A net 172.16.0.0 - 172.31.255.255 16 contiguous class Bs


192.168.0.0 192.168.255.255 256 contiguous class Cs

Connectivity provided by Network AddressTranslator (NAT) translates outgoing private IP address to Internet IP

address, and a return Internet IP address to a private

address Only for TCP/UDP packets

Special Purpose IP AddressesSpecial Purpose IP Addresses


71/200

Several Addresses within the classes arereserved for special use.

0.0.0.0 :Source IP Addr. Just after Boot network part of dest. Addr.= 0 :Source and

Destination are in same network.


Dest. Addr.=255.255.255.255 :Broadcast inSenders network.

host part of Dest.=111 : Broadcast indestination network.

Dest. Addr. = 127.anything : Loop Back

Special Purpose AddressesSpecial Purpose Addresses--ListList


72/200

Address Block Present Use Reference0.0.0.0/8 "This" Network [RFC1700, page 4]10.0.0.0/8 Private-Use Networks [RFC1918]14.0.0.0/8 Public-Data Networks [RFC1700, page 181]24.0.0.0/8 Cable Television Networks39.0.0.0/8 Reserved, subject to allocation [RFC1797]127.0.0.0/8 Loop back [RFC1700, page 5]128.0.0.0/16 Reserved but subject to allocation169.254.0.0/16 Link Local


172.16.0.0/12 Private-Use Networks [RFC1918]

191.255.0.0/16 Reserved but subject to allocation 192.0.0.0/24 Reserved but subject to allocation 192.0.2.0/24 Test-Net192.88.99.0/24 6to4 Relay Anycast [RFC3068]192.168.0.0/16 Private-Use Networks [RFC1918]198.18.0.0/15 Network Interconnect Device Benchmark Testing [RFC2544]223.255.255.0/24 Reserved but subject to allocation 224.0.0.0/4 Multicast [RFC3171]240.0.0.0/4 Reserved for Future Use [RFC1700]

Class Inter Domain RoutingClass Inter Domain Routing

(CIDR)(CIDR)


73/200

( )( )

Many organization have > 256 computersbut few have more than several thousand

Instead of giving class B (16384 nets) givesufficient conti uous class C addresses to


satisfy needs < 256 addresses assign 1 class C

< 8192 addresses assign 32 contiguous Class Cnets

IP addressing: CIDRIP addressing: CIDR


74/200

Classful addressing: inefficient use of address space, address space exhaustion

e.g., class B net allocated enough addresses for 65K hosts,even if only 2K hosts in that network

CIDR: Classless Inter Domain Routing (RFC1519)


network portion of address of arbitrary length

address format: a.b.c.d/x, where x is # bits in networkportion of address

11001000 00010111 00010000 00000000

network

part

host

part

200.23.16.0/23

Bit Masks and Subnet MasksBit Masks and Subnet Masks


75/200

In a production environment this prefix typicallyvaries in length from 8 to 30 bits

/16 = 255.255.0.0/17 = 255.255.128.0/18 = 255.255.192.0/19 = 255.255.224.0

/24 = 255.255.255.0/25 = 255.255.255.128/26 = 255.255.255.192/27 = 255.255.255.224

/8 = 255.0.0.0/9 = 255.128.0.0/10 = 255.192.0.0/11 = 255.224.0.0


/30yields two usable hosts and is used for WAN connections

/20 = 255.255.240.0

/21 = 255.255.248.0/22 = 255.255.252.0/23 = 255.255.254.0

/28 = 255.255.255.240

/29 = 255.255.255.248/30 = 255.255.255.252/31 = not usable/32 = not usable

/12 = 255.240.0.0

/13 = 255.248.0.0/14 = 255.252.0.0/15 = 255.254.0.0

Network Prefix Equivalent Number of Class Addresses Number of Hosts

Prefix Equivalents


76/200

q

/27 1/8th of a Class C 32

/26 1/4th of a Class C 64

/25 1/2 of a Class C 128

/24 1 Class C 256

/23 2 Class C 512

/22 4 Class C 1,024

/21 8 Class C 2,048

/20 16 Class C 4,096

/19 32 Class C 8,192


/18 64 Class C 16,384

/17 128 Class C 32,768

/16 256 Class C or 1 Class B 65,536

/15 512 Class C or 2 Class B 131,072

/14 1,024 Class C or 4 Class B 262,144

/13 2048 Class C or 8 Class B 524,288

/12 4096 Class C or 16 Class B 1,048,576/11 8192 Class C or 32 Class B 2,097,152

/10 16384 Class C or 64 Class B 4,194,304

/9 32768 Class C or 128 Class B 8,388,608

/8 65,536 Class C or 256 Class B or 1 Class A 16,777,216

ProtocolsProtocols


77/200

Class-full Routing Protocols Classless Routing Protocol

RIP version1 RIP version2

IGPR EIGPR


EGP OSPF

BGP3 BGP4

IS-IS

ExamplesExamples


78/200


IP addresses: how to get one?IP addresses: how to get one?


79/200

Q: How does hostget IP address?

IP addr. is configures into host by admin. in a file Wintel: control-panel->network->configuration-


-

UNIX: /etc/rc.config

DHCP: Dynamic Host Configuration Protocol (RFC2131):

dynamically get address from as server plug-and-play

Subnetting (Extended Network Prefix)Subnetting (Extended Network Prefix)


80/200

Q: How an organization gets network part of IP addr?A: It gets allocated portion of its ISPs address

space.

'

The ISP have been allocated the address block


. . .

Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23

... .. . .

Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23

The ISP divides the block into 8 smaller addr.blocks (subnets) and gives them to 8

organization.

Hierarchical addressing: route aggregationHierarchical addressing: route aggregation


81/200

Hierarchical addressing allows efficientadvertisement of routing information:

Send me anything

200.23.16.0/23

Organization 0

Organization 1

route aggregation orroute summarization.


w a ressesbeginning

200.23.16.0/20

200.23.18.0/23

200.23.30.0/23

Organization 7Internet

ISP2 Send me anythingwith addressesbeginning199.31.0.0/16

200.23.20.0/23Organization 2

...

...

199.31.0.0/16

ISP1200.23.16.0/20

Hierarchical addressing: more specific routesHierarchical addressing: more specific routes

ISP2 has a more specific route to Organization 1


82/200

Send me anythingwith addressesbeginning

200.23.16.0/23

Organization 0

The routers in Internet use a longest prefix matching rule, and routetoward ISP2, as it advertises the longest (more specific) address prefixthat matches the destination address.


200.23.16.0 /20

200.23.18.0/23

200.23.30.0/23

ISP1

Organization 7 Internet

Organization 1 ISP2

Send me anything

with addressesbeginning 199.31.0.0/16or 200.23.18.0 /23

200.23.20.0/23

Organization 2

...

.

..

23 bits

20 bits

Subnet MaskSubnet Mask--11


83/200

A subnet mask is applied to the host bits todetermine how the network is subnetted, e.g. if the host is: 137.138.28.228, and the subnet mask

is 255.255.255.0 then the right hand 8 bits are for thehost (255 is decimal for all bits set in an octet)


Host addresses of all bits set or no bits set,

indicate a broadcast, i.e. the packet is sent to allhosts.

Subnet MaskSubnet Mask--22


84/200

ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20ISPs subnet mask 11111111 11111111 11110000 00000000 255.255.240.0

Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23


Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23

... .. . .Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23

Ors subnet mask 11111111 11111111 11111110 00000000 255.255.254.0

Network part of an IP address= subnet mask & IP address

IP addressing: ICANNIP addressing: ICANN


85/200

Q: How does an ISP get block of addresses?

A: ICANN: Internet Corporation for Assigned


allocates addresses manages DNS

assigns domain names, resolves disputes

CIDR: Subneting ExampleCIDR: Subneting Example


86/200

You are assigned the CIDR address 200.32.108.0 /22 and

you must support the network shown in the diagram.

Create an addressing scheme that will meet the diagramrequirements.

100 computers


100 computers

100 computers

300 computers

CIDR: Subneting ExampleCIDR: Subneting Example

(Questions)(Questions)


87/200

Given the CIDR address 200.32.108.0 /22

How many Class C networks do we have? 3 classes

How many host addresses do we have? 4x254 addresses What is the largest LAN requirement? 300 addresses


Host required - 300, 100, 100, 100, and 3 WAN links

0 0


88/200

200.32.108.0 200.32. 110.0

255 255


0 0

255 255

200.32. 109.0 200.32. 111.0

0 0


89/200

200.32. 110.0

255 255

osts

08.0/

23

200.32.108.0


0 0

255 255

3

00

200.32.

1

200.32. 109.0

200.32. 111.0

0 0 128

2525


90/200

255 255

osts

08.0/

23

127

1

00h

osts

200.

32.

110.

0/

25

1

00h

osts

200.3

2.

110.

128/

200.32.108.0 200.32. 110.0


0 0

255 255

3

00

200.32.

1

200.32. 109.0

200.32. 111.0

0 0 128

25 /2

5


91/200

255 255

osts

08.

0/

23

127

1

00h

osts

200.

32.

110.

0/

25

1

00h

osts

200.3

2.

110.

128/2

200.32.108.0 200.32. 110.0


0 0

255 255

3

00

200.32.

1

127

128

100h

osts

200.3

2.

111.0/

25

200.32. 109.0 200.32. 111.0

0 0 128

25 /25


92/200

255 255

osts

08.

0/

23

127

1

00h

osts

200.

32.

110.

0/

25

1

00h

osts

200.3

2.

110.

128/

200.32.108.0 200.32. 110.0


0 0

255 255

3

00

200.32.

1

127

128

100h

osts

200.3

2.

111.0/

25

191192

223

224

248

247

243252

251244

WAN links/30

240239

200.32. 109.0 200.32. 111.0


93/200

Company XYZ needs to address 400 hosts

Supernetting ExampleSupernetting Example--11


94/200

Company XYZ needs to address 400 hosts. Its ISP gives them two contiguous Class C addresses:

207.21.54.0/24 207.21.55.0/24

Company XYZ can use a prefix of 207.21.54.0 /23 to supernet these twocontiguous networks. (Yielding 510 hosts) 207.21.54.0 /23

207.21.54.0/24


. . .

23 bits in common

Supernetting ExampleSupernetting Example--22

addressing authority of ISP include XYZ


95/200

addressing authority of ISP,include XYZ,be advertized to Internet as a single supernt


CIDR and the ProviderCIDR and the Provider

example of route aggregation


96/200

advertising address: a.b.c.d/x


IPIP datagram formatdatagram format

ver l h

32 bitsIP protocol versionNumber[4bits]

header length total datagramlength (bytes)head type of


97/200

ver length

16-bit identifier

Checksum: 1s add of

16bits words in header

time to

live32 bit source IP address

header length(bytes)[4bits]

max number

fragmentation/Reassembly/

DF, MF Flags

total datagramlength (bytes)

upper layerprotocol

head.len

type ofservice

type of data: Priority [3bits]Delay[1bit]

Throughput[1bit]Reliability[1bit]

flags fragmentoffset

upper

layer


data(variable length,typically a TCP

or UDP segment)

rema n ng o s(decremented at

each router)

o e verpayload to(rfc 1700)

es na on a ress

Options (if any)

e.g. timestamp,record routetaken, specifylist of routersto visit.

how much overheadwith TCP?

20 bytes of TCP 20 bytes of IP

= 40 bytes + applayer overhead

A packet is unique in Internet by:Id + S. IP Add + D. IP Add + Upper L.

1 :ICMP6 :TCP17 :UDP

IP Fragmentation & ReassemblyIP Fragmentation & Reassembly

network links have MTU


98/200

network links have MTU(max.transfer size) - largestpossible link-level frame.

different link types,

different MTUs large IP datagram divided

(fragmented) within net

fragmentation:

in: one large datagramout: 3 smaller datagrams


one datagram becomes

several datagrams reassembled only at final

destination

IP header bits used toidentify, order related

fragments

reassembly

IP Fragmentation and ReassemblyIP Fragmentation and Reassembly

0.3979

data20 Byte


99/200

ID=x

offset=0

fragflag=0

length=4000

ID offsetfragflaglength

Example

4000 byte

datagram MTU = 1500 bytes

4000 Bytes

0.1479


ID=x

offset=1480

fragflag=1

length=1500

ID=x

offset=2960

fragflag=0

length=1040

One large datagram becomes3 smaller datagrams.

14802959

Network managers or users identify network problems. On f th m st f ntl s d d b in t ls in k s th

ICMPICMP: Internet Control Message Protocol: Internet Control Message Protocol


100/200

Networ managers or users dent fy networ problems. One of the most frequently used debugging tools invokes the

ICMP echo requestand echo replymessages.

A host or router sends an ICMP echo request message to aspecified destination.


The command users invoke to send ICMP echo requests is

namedping. Sophisticated versions of ping send a series ofICMP echo requests, capture responses, and providestatistics about datagram loss. They allow the user tospecify the length of the data being sent and the interval

between requests. Less sophisticated versions merely sendone ICMP echo request and await a reply.

Any machine that receives an echo request formulates an

echo reply and returns it to the original sender. The requestcontains an optional data area; the reply contains a copy of

ICMP (Cont.)ICMP (Cont.)


101/200

p y g qcontains an optional data area; the reply contains a copy ofthe data sent in the request. The echo request andassociated reply can be used to test whether a destination isreachable and responding. Because both the request andreply travel in IP datagrams, successful receipt of a replyverifies that major pieces of the transport system work.


,the datagram.

Second, intermediate routers between the source anddestination must be operating and must route thedatagram correctly.

Third, the destination machine must be running (at least

it must respond to interrupts), and both ICMP and IPsoftware must be working.

Finally, all routers along the return path must havecorrect routes.

ICMP (Cont.)ICMP (Cont.)

The Internet Control Message Protocol allows routers to send error or

control messages to other routers or hosts; ICMP providescommunication between the Internet Protocol software on one machine


102/200

g pand the Internet Protocol software on another.

When a datagram causes an error, ICMP can only report the error

condition back to the original source of the datagram; the source mustrelate the error to an individual application program or take otheraction to correct the problem.


Each ICMP message has its own format. They all begin with the same

three fields: an 8-bit TYPE field that identifies the message, an 8-bit CODE field that provides further information about the

message type, a 16-bit CHECKSUM field (ICMP uses the same additive checksum

algorithm as IP, but the ICMP checksum only covers the ICMPmessage). In addition, ICMP messages that report errors always include the

header and first 64 data bits of the datagram causing the problem.

ICMP: TYPE, CODEICMP: TYPE, CODE

Type Code description0 0 echo reply (ping)


103/200

yp p0 0 echo reply (ping)3 0 dest. network unreachable3 1 dest host unreachable

3 2 dest protocol unreachable3 3 dest port unreachable3 6 dest network unknown


3 7 dest host unknown

4 0 source quench (congestioncontrol - not used)

8 0 echo request (ping)9 0 route advertisement

10 0 router discovery11 0 TTL expired12 0 bad IP header

ICMPs Message Format: an exampleICMPs Message Format: an example


104/200

OPTIONAL DATAis a variable length field that contains data to be returned to thesender. An echo reply always returns exactly the same data as was received in therequest. IDENTIFIERand SEQUENCE NUMBERare used by the sender to matchreplies to requests. The value of the TYPEfield specifies whether the message is a

ICMP echo request or reply message format.


The ICMP message is encapsulated in an IP datagram, which is furtherencapsulated in a frame for transmission. To identify ICMP, the datagramprotocol field contains the value 1.

reques or a rep y .

DHCPDHCP: Dynamic Host Configuration Protocol: Dynamic Host Configuration Protocol


105/200

Goal: allow host to dynamicallyobtain its IP addressfrom network server when it joins network

Can renew its lease on address in useAllows reuse of addresses (only hold address while connected

an on


Support for mobile users who want to join network (more

shortly)DHCP overview:

host broadcasts DHCP discover msg

DHCP server responds with DHCP offer msg host requests IP address: DHCP request msg

DHCP server sends address: DHCP ack msg

DHCP clientDHCP client--server scenarioserver scenario


106/200

223.1.1.1

223.1.1.2223.1.1.4 223.1.2.9

223.1.2.1

DHCPserver

A


223.1.1.3

223.1.2.2

223.1.3.2223.1.3.1

223.1.3.27 arriving DHCPclient needsaddress in thisnetwork

B

E

DHCP clientDHCP client--server scenarioserver scenario

DHCP server: 223.1.2.5arriving

clientDHCP discoversrc : 0.0.0.0, 68


107/200

,dest.: 255.255.255.255,67 yiaddr: 0.0.0.0transaction ID: 654

DHCP offer

src: 223.1.2.5, 67dest: 255.255.255.255, 68yiaddrr: 223.1.2.4transaction ID: 654


time

Lifetime: 3600 secsDHCP request

src: 0.0.0.0, 68dest:: 255.255.255.255, 67yiaddrr: 223.1.2.4transaction ID: 655Lifetime: 3600 secs

DHCP ACK

src: 223.1.2.5, 67dest: 255.255.255.255, 68yiaddrr: 223.1.2.4transaction ID: 655Lifetime: 3600 secs

NAT: Network Address TranslationNAT: Network Address Translation


108/200

10.0.0.1

10.0.0.210.0.0.4

local network(e.g., home network)

10.0.0/24

rest ofInternet


10.0.0.3

138.76.29.7

Datagrams with source ordestination in this network

have 10.0.0/24 address forsource, destination (as usual)

Alldatagrams leavinglocalnetwork have same single source

NAT IP address: 138.76.29.7,different source port numbers


l l k


109/200

Motivation: local network uses just one IP address asfar as outside word is concerned:

no need to be allocated range of addresses from ISP:- just one IP address is used for all devices


without notifying outside world can change ISP without changing addresses of

devices in local network

devices inside local net not explicitly addressable,visible by outside world (a security plus).


Implementation: NAT router must:


110/200

outgoing datagrams: replace(source IP address, port#) of every outgoing datagram to (NAT IP address,new port #). . . remote clients/servers will respond using (NAT

[email protected]@iust.ac.ir Network LayerNetwork Layer [email protected]

IUST-Network Layer

, .

remember (in NAT translation table)every (sourceIP address, port #) to (NAT IP address, new port #)translation pair

incoming datagrams: replace(NAT IP address, newport #) in dest fields of every incoming datagramwith corresponding (source IP address, port #)stored in NAT table


1: host 10 0 0 1NAT translation table2 N T


111/200

S: 10.0.0.1, 3345D: 128.119.40.186, 80

1: host 10.0.0.1sends datagram to128.119.40, 80

WAN side addr LAN side addr

138.76.29.7, 5001 10.0.0.1, 3345

2: NAT routerchanges datagramsource addr from

10.0.0.1, 3345 to138.76.29.7, 5001,updates table


IUST-Network Layer

. . .

10.0.0.2

10.0.0.3

1

10.0.0.4

138.76.29.7 S: 128.119.40.186, 80D: 10.0.0.1, 3345 4

S: 138.76.29.7, 5001

D: 128.119.40.186, 802

S: 128.119.40.186, 80D: 138.76.29.7, 5001 3

3: Reply arrivesdest. address:138.76.29.7, 5001

4: NAT routerchanges datagramdest addr from138.76.29.7, 5001 to 10.0.0.1, 3345


16 bit t b fi ld


112/200

16-bit port-number field: 60,000 simultaneous connections with a single

LAN-side address! NAT is controversial:


IUST-Network Layer

routers should only process up to layer 3

violates end-to-end argument NAT possibility must be taken into account by app

designers, eg, P2P applications

address shortage should instead be solved byIPv6

ChapterChapter 44 OutlineOutline



113/200





.

4.5.1 Intra-AS routing: RIP and OSPF

4.5.2 Inter-AS routing: BGP

4.6 Whats Inside a Router?

4.7 IPv6

4.8 Multicast Routing

4.9 Mobility

Routing in the InternetRouting in the Internet

(RC1812)(RC1812) Requirements for IP Version 4 RoutersRequirements for IP Version 4 Routers

The Global Internet consists of Autonomous Systems


114/200

G a n rn n f u n m u y m(AS) interconnected with each other: Stub AS: small corporation: one connection to other ASs

Multihomed AS: large corporation (no transit): multipleconnections to other ASs


rans prov er, oo ng many s oge er

Two-level routing: Intra-AS: administrator responsible for choice of routing

algorithm within network

Inter-AS: unique standard for inter-AS routing:BGP(RFC1771)

Internet AS HierarchyInternet AS Hierarchy

Intra-AS border (exterior gateway) routers


115/200

C.b

A.a

B.a


Inter-AS (interior gateway) routers

A B

A.ca b

ad

bc

ac

b

IntraIntra--AS RoutingAS Routing

Also known as Interior Gateway Protocols (IGP)


116/200

Also known as Interior Gateway Protocols (IGP)

Most common Intra-AS routing protocols:

RIP: Routing Information Protocol


: pen or es a rs

IGRP: Interior Gateway Routing Protocol (Ciscoproprietary)

RIPRIP ( Routing Information Protocol)( Routing Information Protocol)

Distance vector algorithm


117/200

Distance vector algorithm

Included in BSD-UNIX Distribution in 1982

Distance metric: # of hops (max = 15 hops) Can you guess why?


Distance vectors: exchanged among neighbors every30 sec via Response Message (also calledadvertisement)

Each advertisement: list of up to 25 destination nets

within AS

RIP: ExampleRIP: Example

z


118/200

C

w x y

A D B


Destination Network Next Router Num. of hops to dest.

w A 2y B 2z B 7

x -- 1. . ....

Routing table in D

RIP: ExampleRIP: Example

Dest Next hops

w - -x - -z C 4

Advertisementfrom A to D


119/200

z C 4. ...

w x y

z

A D B


Destination Network Next Router Num. of hops to dest.

w A 2y B 2

z B A 7 5x -- 1. . ....

Routing table in D

RIP: Link Failure and RecoveryRIP: Link Failure and Recovery

If no advertisement heard after 180 sec -->i hb /li k d l d d d


120/200

neighbor/link declared dead

routes via neighbor invalidated

new advertisements sent to neighbors nei hbors in turn send out new advertisements if


tables changed)

link failure info quickly propagates to entire net poison reverse used to prevent ping-pong loops

(infinite distance = 16 hops)

RIP Table processingRIP Table processing

RIP routing tables managed by application-level


121/200

RIP routing tables managed by application levelprocess called route-d (daemon)

advertisements sent in UDP packets, periodicallyrepeated


physical

link

network forwarding(IP) table

Transprt(UDP)

routed

physical

link

network

(IP)

Transprt(UDP)

routed

forwarding

table

RIP Table example (continued)RIP Table example (continued)

Router:giroflee.eurocom.fr


122/200

Destination Gateway Flags Ref Use Interface

-------------------- -------------------- ----- ----- ------ ---------

127.0.0.1 127.0.0.1 UH 0 26492 lo0

192.168.2. 192.168.2.5 U 2 13 fa0

193.55.114. 193.55.114.6 U 3 58503 le0

192.168.3. 192.168.3.5 U 2 25 qaa0


Three attached class C networks (LANs)

Router only knows routes to attached LANs

Default router used to go up

Route multicast address: 224.0.0.0

Loopback interface (for debugging)

. . . . . . e

default 193.55.114.129 UG 0 143454

OSPFOSPF (Open Shortest Path First)(Open Shortest Path First)

open: publicly available


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Uses Link State algorithm LS packet dissemination

Topology map at each node

Route computation using Dijkstras algorithm


OSPF advertisement carries one entry per neighborrouter

Advertisements disseminated to entire AS (via

flooding) Carried in OSPF messages directly over IP (rather than TCPor UDP

OSPF advanced features (not in RIP)OSPF advanced features (not in RIP)

Security: all OSPF messages authenticated (to


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Security: all OSPF messages authenticated (toprevent malicious intrusion)

Multiple same-cost paths allowed (only one path inRIP)

[email protected]@iust.ac.ir Network LayerNetwork Layer 44--124124

[email protected] IUST-Network Layer

or eac n , mu p e cos me r cs or eren

TOS (e.g., satellite link cost set low for best effort;high for real time)

Integrated uni- and multicast support:

Multicast OSPF (MOSPF) uses same topology database as OSPF

Hierarchical OSPF in large domains.

Hierarchical OSPFHierarchical OSPF


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Hierarchical OSPFHierarchical OSPF

Two-level hierarchy: local area, backbone.

Li k d i l i


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Link-state advertisements only in area

each nodes has detailed area topology; only knowdirection (shortest path) to nets in other areas.



in own area, advertise to other Area Border routers.

Backbone routers: run OSPF routing limited tobackbone.

Boundary routers: connect to other ASs.

InterInter--AS routing in the Internet:AS routing in the Internet: BGPBGP

BGP

R4

R5


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AS2(OSPF

intra-AS

AS1(RIP intra-AS routing)

BGP

AS3(OSPF intra-AS

routing)

BGPR3

R5



Figure 4.5.2-new2: BGP use for inter-domain routing

routing)

R1 R2

Internet interInternet inter--AS routing: BGPAS routing: BGP

BGP (Border Gateway Protocol): thede factost d d


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standard Path Vector protocol:

similar to Distance Vector protocol each order Gatewa broadcast to nei hbors



(peers) entire path(i.e., sequence of ASs) to

destination BGP routes to networks (ASs), not individual

hosts E.g., Gateway X may send its path to dest. Z:

Path (X,Z) = X,Y1,Y2,Y3,,Z

Internet interInternet inter--AS routing: BGPAS routing: BGP

Suppose:gateway X send its path to peer gateway W

W l h ff d b X


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W may or may not select path offered by X

cost, policy (dont route via competitors AS), loopprevention reasons.



,

Path (W,Z) = w, Path (X,Z) Note: X can control incoming traffic by controlling it

route advertisements to peers:

e.g., dont want to route traffic to Z -> dontadvertise any routes to Z

BGP: controlling who routes to youBGP: controlling who routes to you

A

B

WX

legend: providernetwork


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A

C

W

Y

customer

network

[email protected]@iust.ac.irNetwork LayerNetwork Layer 44--130130


A,B,C are provider networks X,W,Y are customer (of provider networks)

X is dual-homed: attached to two networks

X does not want to route from B via X to C .. so X will not advertise to B a route to C

Figure 4.5- BGPnew : a simple BGP scenario

BGP: controlling who routes to youBGP: controlling who routes to you

B

WX

legend: providernetwork


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A

C

W

Y

customer

network


A advertises to B the path AW B advertises to W the path BAW

Should B advertise to C the path BAW? No way! B gets no revenue for routing CBAW since neither

W nor C are Bs customers B wants to force C to route to w via A

B wants to route onlyto/from its customers!

BGP operationBGP operation

Q: What does a BGP router do?


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Receiving and filtering route advertisements from

directly attached neighbor(s). Route selection.


To route to destination X, which path )of

several advertised) will be taken? Sending route advertisements to neighbors.

BGP messagesBGP messages

BGP messages exchanged using TCP.

BGP messages:


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BGP messages:

OPEN: opens TCP connection to peer andauthenticates sender


KEEPALIVE keeps connection alive in absence ofUPDATES; also ACKs OPEN request

NOTIFICATION: reports errors in previous msg;also used to close connection

Why different IntraWhy different Intra-- and Interand Inter--AS routing ?AS routing ?

Policy: Inter-AS: admin wants control over how its traffic


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Inter AS: admin wants control over how its trafficrouted, who routes through its net.

Intra-AS: single admin, so no policy decisions needed


hierarchical routing saves table size, reduced updatetraffic

Performance:

Intra-AS: can focus on performance

Inter-AS: policy may dominate over performance



4 2 Routing Principles


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4.3 Hierarchical Routing4.4 The Internet (IP) Protocol


4.5 Routing in the Internet

4.6 Whats Inside a Router?4.7 IPv6

4.8 Multicast Routing4.9 Mobility

Router Architecture OverviewRouter Architecture Overview

Two key router functions: run routing algorithms/protocol (RIP, OSPF, BGP)


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g g p

switchingdatagrams from incoming to outgoing link


Input Port FunctionsInput Port Functions


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Physical layer:


Decentralized switching: given datagram dest., lookup output portusing routing table in input port memory

goal: complete input port processing at

line speed queuing: if datagrams arrive faster than

forwarding rate into switch fabric

- eve rece on

Data link layer:e.g., Ethernetsee chapter 5

Input Port QueuingInput Port Queuing

Fabric slower that input ports combined -> queueingmay occur at input queues

Head-of-the-Line (HOL) blocking: queued datagram


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Head of the Line (HOL) blocking queued datagramat front of queue prevents others in queue frommoving forward


Three Types of Switching FabricsThree Types of Switching Fabrics


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Switching Via MemorySwitching Via Memory

First generation routers: packet copied by systems (single) CPU

speed limited by memory bandwidth (2 bus


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p m t y m m ry an w t ( ucrossings per datagram)

Input

PortOutput

Port

Memory


System Bus

Modern routers:

input port processor performs lookup, copy intomemory

Cisco Catalyst 8500

Switching Via a BusSwitching Via a Bus


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datagram from input port memoryto output port memory via a shared


us

bus contention: switching speedlimited by bus bandwidth

1 Gbps bus, Cisco 1900: sufficientspeed for access and enterpriserouters (not regional or backbone)

Switching Via An Interconnection NetworkSwitching Via An Interconnection Network

overcome bus bandwidth limitations


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overcome bus bandwidth limitations

Banyan networks, other interconnection netsinitially developed to connect processors in


mu processor

Advanced design: fragmenting datagram into fixedlength cells, switch cells through the fabric.

Cisco 12000: switches Gbps through theinterconnection network

Output PortsOutput Ports


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Bufferingrequired when datagrams arrive fromfabric faster than the transmission rate

Scheduling disciplinechooses among queueddatagrams for transmission

Output port queuingOutput port queuing

8/9/2019

Cn Chp4 [Compatibility Mode]

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