Chap 14 Modified

7/25/2019 Chap 14 Modified

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TCP/IP Protocol Suite 1

Chapter 14Chapter 14

Upon completion you will be able to:

Unicast Routing Protocols:Unicast Routing Protocols:RIP, OSPF, and BGPRIP, OSPF, and BGP

Distinguis between intradomain and interdomain routingUnderstand distance !ector routing and RIPUnderstand lin" state routing and OSPFUnderstand pat !ector routing and BGP

Objectives


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Figure 14.1 #utonomous systems

An autonomous systemis a set of networks and routers undthe control of a single administrative authority!outing within an autonomous system is intradomain routin!outing "etween autonomous systems is interdomain routin


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Figure 14.2 Popular routing protocols


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14.2 DISTANCE VECTOR ROUTING

In distance !ector routing,In distance !ector routing, te least cost route between any two nodes iste least cost route between any two nodes iste route wit minimum distancete route wit minimum distance$ In tis protocol eac node maintains a$ In tis protocol eac node maintains a

!ector %table& o' minimum distances to e!ery node!ector %table& o' minimum distances to e!ery node

(e topics discussed in tis section include:(e topics discussed in tis section include:

Initiali)ationInitiali)ation

SaringSaring

UpdatingUpdating

*en to Sare*en to Sare

(wo+ode -oop Instability(wo+ode -oop Instability

(ree+ode Instability(ree+ode Instability


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Figure 14.3 Distance !ector routing tables


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Figure 14.4 Initiali)ation o' tables in distance !ector routing

In distance vector routing# each node shares its ta"le withits immediate neigh"or periodically $eg every %&s' and whenthere is a change


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Figure 14.5 Updating in distance !ector routing

Step 1( Add cost $)' to ta"le received from neigh"or $C'Step )( Compare *odi+ed Ta"le with ,ld Ta"le $row "y rowIf -e.t node entry is dierent# select the row with the sma

cost If tie# keep the old oneIf -e.t node entry the same# select the new row value $regless of whether new value is smaller or not'


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Figure 14.6 (wo+node instability . wat can appen wit distance !ector routing

oth A and knowwhere 2 is

3ink "etween A and 2fails A updates itsta"le immediately

ut "efore A can tell sends its info to A

A# using 5s info# up0dates its ta"le $errorThen A send its ta"le

to and updates itta"le $more error'

oth routers keep up0dating ta"les# event0ually hitting in+nity I

the meantime# chaos


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Figure 14.6 (wo+node instability . wat can appen wit distance !ector routing

Possi"le Solutions to two0node insta"ility(

1 6e+ne in+nity to "e a much smaller value# such as 1&&Then it doesn5t take too long to "ecome sta"le ut nowyou can5t use distance vector routing in large networks

) Split 7ori8on 9 instead of :ooding entire ta"le to eachnode# only part of its ta"le is sent *ore precisely# if node

thinks that the optimum router to reach 2 is via A# then does not need to advertise this piece of info to A 9 theinfo has already come from A

% Split 7ori8on and Poison !everse 9 -ormally# the distanvector protocol uses a timer If there is no news a"out a

route# the node deletes the route from its ta"le So whennever hears from a"out the route to 2# it deletes itInstead# -ode still advertises the value for 2# "ut if thesource of info is A# it replaces the distance with in+nity#saying ;6o not use this value< what I know a"out this routcomes from you=


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Figure 14.7 (ree+node instability . no solutions ere/


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14.3 RIP

(e Routing In'ormation Protocol(e Routing In'ormation Protocol %RIP& is an%RIP& is an intradomainintradomain routingroutingprotocolprotocol used inside an autonomous systemused inside an autonomous system$ It is a !ery simple protocol$ It is a !ery simple protocol

based on distance !ector routingbased on distance !ector routing$$


RIP 0essage FormatRIP 0essage Format

Re1uests and ResponsesRe1uests and Responses

(imers in RIP(imers in RIP

RIP 2ersion 3RIP 2ersion 3

4ncapsulation4ncapsulation


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Figure 14.8 45ample o' a domain using RIP

-ote themetric usedhere for Costis simply thehop count


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Figure 14.9 RIP message 'ormat

Command( re>uest $1' or response $)'?ersion( 1 or ) $version ) shown in a couple slides'@amily( TCP/IP has value )-etwork address( address of the destination network6istance( hop count from the advertising router to the destinanetwork


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Figure 14.10 Re1uest messages

A re>uest message is sent "y a router that has ust come up o

a router that has some time0out entries

A response message is sent in answer to a re>uest $solicited resor simply every %& seconds $unsolicited' !esponse message forshown in previous slide


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Figure 67$66 sows te update message sent 'rom router R6 torouter R3 in Figure 67$8$ (e message is sent out o' inter'ace

69$6$$3$

Example1

See Next Slide

(e message is prepared wit te combination o' split ori)on

and poison re!erse strategy in mind$ Router R6 as obtainedin'ormation about networ"s 6;


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Figure 14.11 Solution to 45ample 6

7opB1 means destis unreacha"le $only

works on smallernetworks'


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Figure 14.12 RIP timers

Periodic timer( controls the advertising of regular updates

D.piration timer( governs the validity of a route Ehen arouter receives info# sets timer to 1F&s -o update within1F&sG !oute set to 1# which means unreacha"le

Har"age collection timer( Set to 1)&s after route set to 1Ehen timer e.pires# then toss route info


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# routing table as 3 entries$ It does not recei!e in'ormationabout 'i!e routes 'or 3 s$ >ow many timers are running at

tis time?

Example2

Solution

(e 36 timers are listed below:

Periodic timer: 6

45piration timer: 3 @ < A 6


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Figure 14.13 RIP !ersion 3 'ormat

-ote( ?ersion ) supports su"net masks!oute tag( carries information such as the AS num"erSo it allows !IP to receive info from an interdomain routing prot


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Figure 14.14 #utentication

@@@@ in family +eld indicates that the message carriesauthentication info and not routing info

Authentication type( de+nes the protocol used for authenticatioAuthentication data( contains the actual authentication data$eg password'


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RIP uses te ser!ices o' UDP onwell+"nown port


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14.4 LINK STATE ROUTING

In lin" state routing, i' eac node in te domain as te entire topologyIn lin" state routing, i' eac node in te domain as te entire topologyo' te domain, te node can use Di"straCs algoritm to build a routingo' te domain, te node can use Di"straCs algoritm to build a routing

table$table$


Building Routing (ablesBuilding Routing (ables


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Figure 14.15 oncept o' lin" state routing

oncept o' lin" state routing

Dvery router has knowledge a"out the network# "ut from

its own perspective


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Figure 14.16 -in" state "nowledge

Dach router knows $maintains' its states of its links

Dach router :oods this info $via a 3ink State Packet' to otherouters periodically $when there is a change in the topology#or every & to 1)& minutes'

Each routertakes in this data and# using 6ikstra5s

algorithm# creates the shortest path tree and correspondingrouting ta"le


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Figure 14.17 Di"stra algoritm


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Figure 14.18 45ample o' 'ormation o' sortest pat tree


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(able 67$6(able 67$6 Routing table 'or node #Routing table 'or node #

-ow let5s try using the 6ikstra5s algorithm introduced inT6C %1


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14.5 OSPF

(e Open Sortest Pat First %OSPF& protocol is an(e Open Sortest Pat First %OSPF& protocol is an intradomainintradomainrouting protocol based on lin" state routingrouting protocol based on lin" state routing$ Its domain is also an$ Its domain is also an

autonomous system$autonomous system$


#reas#reas

0etric0etric

(ypes o' -in"s(ypes o' -in"s

Grapical RepresentationGrapical Representation

OSPF Pac"etsOSPF Pac"ets-in" State Update Pac"et-in" State Update Pac"et

Oter Pac"etsOter Pac"ets

4ncapsulation4ncapsulation

Fi 14 19 # i


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Figure 14.19 #reas in an autonomous system

,SP@ divides an autonomous system into areas All networinside an area must "e connectedArea "order router( The router at the "order of an area

ack"one( The area that is connected to all other areas"ack"one routers( !outers inside the "ack"oneAS "oundary router( !outer that is connecting two ASThe cost associated with a route is called the metric *etricould "e min delay# ma. thruput# etc

Fi 14 21 P i t t i t li "


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Figure 14.21 Point+to+point lin"

-o hosts in "etween< T01 connection common

Fi 14 22 ( i t li "


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Figure 14.22 (ransient lin"

A network with several routers attached to it< all 3A-s and somehave transient links< " is unrealistic "ecause too many advertiseIn c# one of the routers also "ecomes la"eled the designated rout

Fi 14 23 St b li "


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Figure 14.23 Stub lin"

A network that is connected to only one router

and is a special case of the transient

?irtual link( A link that is created "etween two routers"y an administration using a longer path that pro"a"lygoes through several router in case the link "etweenthese two routers is "roken


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Figure 14.24 45ample o' an #utonomous System and its grapical

representation in OSPF

Ehat kind of networks are the dotted linesGAre there any stu" networks hereG Ehat are the transient netwo

Figure 14 25 (ypes o' OSPF pac"ets


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Figure 14.25 (ypes o' OSPF pac"ets

,SP@ works "y transferring packets Ehat are the dieretypes of packetsG

The link state update packets are the most important# "ut seethe ne.t slide

Res!"ds t! # li"$%st#te re&uest


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When a router is

connect to the system or

after a failure, it cannot

wait for all link statepackets before making

its own database and

calculating its routing

table. Neighbors will

send it a database

description when they

receive a hello messagefrom it for the first time

(not the full database

but like an outline about

links). rom this, the

router can then ask for

information it does not

have.

!sed to create

neighbor

relationshipsand to test the

reachability of

neighbors.

"he first step

in link staterouting.

#e$uests pieces of the

topological database from

neighbor routers. "hese

messages are e%changed

after a router discovers

(by e%amining database&

description packets) that

parts of its topological

database are out of date.

&

#c$et. '(ese )ess#ges #ls! #re used

*!r t(e regul#r disers#l !* +S,s.

Sever#l +S,s c#" be i"cluded -it(i" #

si"gle li"$%st#te ud#te #c$et.

'ck&

nowledges

link&stateupdate

packets.

"ype * +

Figure 14 26 OSPF common eader


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Figure 14.26 OSPF common eader

?ersion( ?ersion of ,SP@ $Current version is )'Type( Type of the packet $1 to 'Area identi+cation( The area within which the routing

takes place

Checksum( entire packet e.cluding the Auth type and AuthAuthentication( 6e+nes the authentication protocol used inthis area & 0J -one# 1 0J PasswodAuthentication( Actual value of the authentication dataAuthentication type B & 0J &s# Authentication type B 1 0Jeight character password

Figure 14 27 -in" state update pac"et


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Figure 14.27 -in" state update pac"et

This is the general form of the link state update packet

It is used "y a router to advertise the state of its links

-ote that this packet contains one or more 3SAs $the yellowpart'

Figure 14 28 -S# general eader


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Figure 14.28 -S# general eader

This is the general header for each 3SA

3ink state age0seconds elapsed since this message was +rstgeneratedD( if 1# then this area is a stu" area

T( if 1# router can handle multiple types of service3ink state type( 1$router link'# )$network link'# etc $ne.t slide'Advertising router( IP address of router advertising this msg3ink state se>uence num"er( simply a se>uence num"erChecksum is actually "ased on @letcher5s checksum

-ink&state advertisement (-ink&state update) types


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R!uter +i"$s (#-) ("ype ) are generated by all routers. "hese links describe the

state of the router interfaces inside a particular area. "hese links are only flooded

inside the routers area.

Net-!r$ +i"$s (N-) (type ) are generated by a /# (/esignated #outer) of a

particular segment0 these are an indication of the routers connected to that segment.

Su))#r +i"$s (1-) are the inter&area links (type *)0 these links will list the

networks inside other areas but still belonging to the autonomous system.

1ummary links are in2ected by the '3# ('rea 3order #outer) from the backboneinto other areas and from other areas into the backbone. "hese links are used for

aggregation between areas.

'1 boundary router summary links are type + links that point to the '13#

('utonomous 1ystem 3oundary #outer). "his is to make sure that all routers know

the way to e%it the autonomous system.

4%ternal -inks (4-) (type ), these are in2ected by the '13# into the domain.

Figure 14 29 Router lin"


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Figure 14.29 Router lin"

This is a router link 3SA $one of the kinds of 3SAs'It is used to de+ne the links of a true router to announce info

all of its links and what is at the other side of the link $neigh

Figure 14 30 Router lin" -S#


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Figure 14.30 Router lin" -S#

@or what to enter in 3ink I6# 3ink data#and 3ink type# see the ne.t slide

6efault typeof service


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(able 67$3(able 67$3 -in" types, lin" identi'ication, and lin" data-in" types, lin" identi'ication, and lin" data


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Gi!e te router lin" -S# sent by router 6$37$E$; inFigure 67$96$

Example3

Solution

(is router as tree lin"s: two o' type 6 %point+to+

point& and one o' type 9 %stub networ"&$ Figure 67$93

sows te router lin" -S#$

See Next Slide

See Figure 14.32

Figure 14.31 45ample 9


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Figure 14.31 45ample 9



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Figure 14.33 etwor" lin" %second "ind o' -S#&


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g % ' &

A network link 3SA de+nes the links of a network and

is generated "y the designated router $6!'

Figure 14.34 etwor" lin" ad!ertisement 'ormat


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g '


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Gi!e te networ" lin" -S# in Figure 67$9


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g p



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g p


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In Figure 67$9E, wic router%s& sends out router lin" -S#s?

Example5

Solution

#ll routers ad!ertise router lin" -S#s$

a$R6 as two lin"s, 6 and 3$b$R3 as one lin", 3$

c$R9 as two lin"s, 3 and 9$

See Next Slide

Figure 14.37 45ample < and 45ample =


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In Figure 67$9E, wic router%s& sends out te networ" lin"-S#s?

Example6

Solution

#ll tree networ" must ad!ertise networ" lin"s: a$#d!ertisement 'or 6 is done by R6 because it is te only

attaced router and tere'ore te designated router$

b$#d!ertisement 'or 3 can be done by eiter R6, R3, or R9,

depending on wic one is cosen as te designated router$

c$#d!ertisement 'or 9 is done by R9 because it is te only

attaced router and tere'ore te designated router$

Figure 14.38 Summary lin" to networ" -S# %tird "ind o' -S#&


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The summary link to network 3SA is used "y the area "orderrouter to announce the e.istence of other networks outsideits area

Figure 14.39 Summary lin" to networ" -S#


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Figure 14.40 Summary lin" to #S boundary router -S# %'ourt "ind o' -S#&


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The summary link to AS "oundary 3SA is used to announce the routAS "oundary router So a router inside an area can send a packet othe AS

Figure 14.41 Summary lin" to #S boundary router -S#


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This packet de+nes the network to which the AS "oundary rouis attached If a message can reach the network# it can "e pick

"y the AS "oundary router

Figure 14.42 45ternal lin" -S# %'i't "ind o' -S#&


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This packet provides info a"out the networks that are availa"leoutside AS to the routers inside the AS The AS "oundary router:oods the AS with the cost of each network outside the AS usinga routing ta"le created "y an interdomain routing protocol

Figure 14.43 45ternal lin" -S#


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Dach advertisement announces one single networkIf there is more than one network# separate announcementsare made

The AS "oundary router may de+ne a forwarding router that canprovide a "etter route to the destination The packet also can incan e.ternal route tag used "y other protocols "ut not ,SP@

Figure 14.44 >ello pac"et %(ype 6 OSPF pac"et&


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Ksed to create neigh"orhood relationships and to testthe reacha"ility of neigh"ors-etwork mask( 6e+nes the mask of the network overwhich the hello message is sent

7ello interval( num"er of seconds "etween hellomessageD B 1( the area is a stu" networkT B 1( the router supports multiple metrics


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Priority( 6e+nes the priority of the router to "e adesignated router The router with the highest priority ischosen as the designated router The router with thesecond highest priority is chosen as the "ackup designatedrouter If the value of this +eld is it means the routernever wants to "e a designated or a "ackup designatedrouter

6ead interval( 6e+nes the num"er of seconds that mustpass "efore a router assumes that a neigh"or is dead

6esignated router IP address( The IP address of thedesignated router for the network over which the messageis sent

ackup designated router IP address( The IP address of the"ackup designated router for the network over which themessage is sent

-eigh"or IP address( 6e+nes the routers that agreed to "ethe neigh"ors of the sending router $the routers that send

hello messages to the sending router

Figure 14.45 Database description pac"et


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Ehen a router is connected to the system for the +rsttime or after a failure# it needs a complete link statedata"ase immediatelyAfter a router is connected to the system# it sends hellopackets to its neigh"ors and since this the +rst time theneigh"ors hear from it# they send a data"ase descriptionmessage

A data"ase description message only gives an outlinea"out each line in the data"aseThe new router e.amines the outline and +nds out whichlines of information it doesn5t have It then sends one ormore link state re>uest packets to get full info a"out

that particular link


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D B 1( means the advertising router is an AS "oundaryrouter $D stands for D.ternal'

B 1( means the advertising router is an area "orderrouter

I $initiali8ation' B 1 ( means this is the +rst message

* $more' B 1 ( means this is not the last message ecausethe data"ase description can "e very long# its contents can"e divided into several messages

*/S $master/slave' :ag( it indicates to the origin of thepacket1 B master# & B slave

*essage se>uence num"er( contains the S- of themessage Ksed to match a re>uest to a response

3SA header( Already discussed in the link state updatemessage section The header gives an outline a"out each

link# without details It is repeated for each link in the linkstate data"ase

Figure 14.46 -in" state re1uest pac"et %(ype 9 OSPF pac"et&


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Ehen a router needs information a"out a speci+c route

or routers# it sends a link state re>uest packet The replyis a link state update packet

The three +elds here are part of the 3SA header which arealready discussed

Figure 14.47 -in" state ac"nowledgment pac"et %(ype < OSPF pac"et&


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ACLs for every link state update packet

The two sections are suMcient to acknowledge a packet


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OSPF pac"ets are encapsulated in IPdatagrams$

Note:Note:

14 6 PATH VECTOR ROUTING


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14.6 PATH VECTOR ROUTING

Pat !ector routing is similar to distance !ector routing$ (ere is at leastPat !ector routing is similar to distance !ector routing$ (ere is at leastone node,one node, called te spea"er nodecalled te spea"er node, in eac #S tat creates a routing, in eac #S tat creates a routing

table and ad!ertises it to spea"er nodes in te neigboring #Ss$table and ad!ertises it to spea"er nodes in te neigboring #Ss$

Only te spea"er nodes communicate$Only te spea"er nodes communicate$

(e spea"er node ad!ertises te pat, not te metric o' te nodes(e spea"er node ad!ertises te pat, not te metric o' te nodes$$

Figure 14.48 Initial routing tables in pat !ector routing


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Figure 14.49 Stabili)ed tables 'or 'our autonomous systems


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14 7 BGP


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14.7 BGP

Border Gateway Protocol %BGP&Border Gateway Protocol %BGP& is an interdomain routing protocolis an interdomain routing protocol

using pat !ector routing$using pat !ector routing$ It 'irst appeared in 6;8; and as goneIt 'irst appeared in 6;8; and as gone

troug 'our !ersions$troug 'our !ersions$

BGP interconnects tree di''erent types o' #S:BGP interconnects tree di''erent types o' #S:

66$ Stub #S$ Stub #S, e$g$ a corporate networ", e$g$ a corporate networ"

3$3$0ultiomed #S0ultiomed #S, e$g$ a large corporate networ" wit connections to, e$g$ a large corporate networ" wit connections to

multiple #Ss, but does not allow tra''ic to pass tru %transient&multiple #Ss, but does not allow tra''ic to pass tru %transient&

9$9$ (ransit #S(ransit #S + one tat allows transient tra''ic, suc as an Internet+ one tat allows transient tra''ic, suc as an Internetbac"bonebac"bone

Figure 14.50 Internal and e5ternal BGP sessions


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The D0HP session is used to e.change info "etween twospeaker nodes "elonging to two dierent AS

The I0HP session is used to e.change routing info "etweentwo routers inside an AS

Figure 14.51 (ypes o' BGP messages


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Figure 14.52 BGP pac"et eader


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*arker( !eserved for authentication3ength( Total length of the messageType( Type of the packet $1# )# %# or 4'

Figure 14.53 Open message


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The open message is used to create a neigh"orhood relationshi

A router running HP opens a TCP connection with aneigh"or and sends an open message If the neigh"oraccepts the neigh"orhood relationship# it responds with a

keepalive message


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?ersion( The version of HP The current version is

*y autonomous system( 6e+nes the AS num"er

7old time( 6e+nes the ma.imum num"er of seconds thatcan elapse until one of the parties receives a keepalive orupdate message from the other If this time passes# therouter considers the other party dead

HP identi+er( 6e+nes the router that sends the openmessage $usually its IP address'

,ption length( 6e+nes the length of the total optionparameters -o options 0J &s

,ption parameters( Dach option parameter itself has twosu"+elds that are the length of the parameter and theparameter valueThe only option parameter de+ned so far is authentication

Figure 14.54 Update message


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Knfeasi"le routes length( 6e+nes the length of the ne.t+eld

Eithdrawn routes( 3ists all the routes that must "e deletedfrom the previously advertised list

Path attri"utes length( 6e+nes the length of the ne.t +eld

Path attri"utes ( 6e+nes the attri"utes of the path $route'to the network whose reacha"ility is "eing announced inthis message

-etwork layer reacha"ility information( 6e+nes thenetwork that is actually advertised "y this message It has

a length +eld $the num"er of "its in the pre+.' and an IPaddress pre+. $common part of the network address'

D. -etwork address B 1%1FN&/)43ength B )4# IP address pre+. B 1%1FN


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BGP supports classless addressing andIDR$

Note:Note:

Figure 14.55 eepali!e message


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The routers running HP e.change keepalive messagesregularly and "efore their hold times e.pire to tell eachother that they are alive

Figure 14.56 oti'ication message


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A noti+cation message is sent "y a router whenever anerror condition is detected or a router wants to close theconnection $-oti+cation message of type Cease'

Drror code( 6e+nes the category of the errorDrror su"code( 6e+nes the type of error in each categoryDrror data( Can "e used to give more diagnostic info a"outthe error

(able 67$9(able 67$9 4rror codes4rror codes


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BGP uses te ser!ices o' (P

on port 6E;$

Note:Note:

Chap 14 Modified

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