Dynamic Routings Cisco

7/18/2019 Dynamic Routings Cisco

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1

Distance Vector vs. LinkState

A B C D

X

E

Distance-vector Routing Protocols: Distance-vector Routing Protocols use simple algorithmsthat calculate a cumulative distance value between routers based on hop count.

Example: Routing Inormation Protocol !ersion 1 "RIPv1# andInterior $atewa% Routing Protocol "I$RP#

Link-state Routing Protocols: &in'-state Routing Protocols use sophisticated algorithms thatmaintain a complex database o internetwor' topolog%.

Example: (pen )hortest Path *irst "()P*# and Intermediate )%stem to Intermediate )%stem "I)-I)#

Hyri! Routing Protocols: +%brid Routing Protocols use a combination o distance-vector andlin'-state methods that tries to incorporate the advantages o both and minimi,e theirdisadvantages.

Example: Enhanced Interior $atewa% Routing Protocol "EI$RP#

Routing Inormation Protocol !ersion "RIPv#

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-distance-vector-routing-protocols.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-routing-information-protocol-rip.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-interior-gateway-routing-protocol-igrp.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-link-state-routing-protocols.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-open-shortest-path-first-ospf-protocol.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-hybrid-routing-protocols.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-enhanced-interior-gateway-routing-protocol-eigrp.php



http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-enhanced-interior-gateway-routing-protocol-eigrp.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-hybrid-routing-protocols.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-open-shortest-path-first-ospf-protocol.php

http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-link-state-routing-protocols.php




http://www.omnisecu.com/cisco-certified-network-associate-ccna/introduction-to-distance-vector-routing-protocols.php



Distance !ector vs. &in')tate

Distance Vector

• /pdates re0uentl%

• Each router is

aware onl% o itsimmediateneighbors

•

)low convergence• Prone to routing

loops

• Eas% to con2gure

Link State

• /pdates are eventtriggered

•

Each router isaware o all otherrouters in the area

• *ast convergence•

&ess sub3ect torouting loops• 4ore di5cult to

con2gure





8

&in' )tate

Example()P*

I)-I)

()P* is used or corporate networ's

I)-I) is used or I)P9s



OSPF



;

(pen )hortest Path *irst "()P*#

()P* is an open standards routing protocol

<his wor's b% using the Di3'stra algorithm

()P* provides the ollowing eatures:

4inimi,es routing update tra5c

=llows scalabilit% "e.g. RIP is limited to 18 hops#

+as unlimited hop count

)upports !&)4>7IDR

/ses +E&&( Pac'ets to inorm neighbors.

Does 4ulticast ??.@[email protected] and ?.@.@.

7onvergence is ast

=llows multi-vendor deplo%ment "open standard#





A

&in' )tate

<here are two t%pes o Pac'ets+ello

&)=9s



1@

()P* +ello

• Bhen router = starts it send +ello pac'et

• +ello pac'ets are received b% all neighbors

• C will write =9s name in its neighbor table

• 7 also process the same wa%

A

B C



11

+ello Pac'ets

• )mall re0uentl% issued pac'ets

• Discover neighbours and negotiate ad3acencies

• !eri% continued availabilit% o ad3acent

neighbours• +ello pac'ets and &in' )tate =dvertisements

"&)=s# build and maintain the topologicaldatabase

• +ello pac'ets are addressed to ?.@[email protected].



1

&in' )tate =dvertisement"&)=#

=n ()P* data pac'et containing lin' state androuting inormation that is shared among ()P*routers

&)=s are shared onl% with routers with whom ithas ormed ad3acencies

&)= pac'ets are used to update and maintainthe topolog% database.





1?

&in' )tate

<here are three t%pe o tableseighbor

<opolog%

Routing



18

<ables

"eig#or

7ontain inormation about the neighbors

eighbor is a router which shares a lin' on

same networ'=nother relationship is ad3acenc%

ot necessaril% all neighbors

&)= updates are onl% when ad3acenc% is

established



1

<ables

$o%ology

7ontain inormation about all networ' and pathto reach an% networ'

=ll &)=9s are entered in to topolog% tableBhen topolog% changes &)=9s are generatedand send new &)=9s

(n topolog% table an algorithm is run to createa shortest path this algorithm is 'nown as )P*or di3'stra algorithm



1;

<ables

Routing $ale

=lso 'nows as orwarding database

$enerated when an algorithm is run on the

topolog% databaseRouting table or each router is uni0ue



1

()P* <erms

&in'

Router ID

eighbours

=d3acenc%

()P* =rea

Cac'bone area

Internal routers

=rea Corder Router"=CR#

=utonomous

)%stem Coundar%Router "=)CR#



1A

&in'

= networ' or router interace assigned to agiven networ'

&in' "interace# will have state

inormation associated with it)tatus "up or down#IP =ddressetwor' t%pe "e.g. *ast Ethernet#

Candwidth=ddresses o other routers attached to

this interace



@

()P* <erm: &in'

A link is a net&ork or router inter'ace assigne! to anygiven net&ork$#is link( or inter'ace( &ill #ave state in'or)ation

associate! &it# it *u% or !o&n+ as &ell as one or )ore ,Pa!!resses





Router ID

<he Router ID "RID# is an IP address used to identi% therouter

7isco chooses the Router ID b% using the highest IP addresso all con2gured loopbac' interaces

I no loopbac' interaces are con2gured with addresses()P* will choose the highest IP address o all activeph%sical interaces.

Fou can manuall% assign the router ID.

<he RID interace 4/)< alwa%s be up thereore loopbac'sare preerred



6

eighbours

eighbours are two or more routersthat have an interace on a commonnetwor'E.g. two routers connected on a serial

lin'

E.g. several routers connected on a

common Ethernet or *rame rela%networ'

7ommunication ta'es placebetween > among neighbours



?

=d3acenc%

= relationship between two routersthat permits the direct exchange oroute updates

ot all neighbours will ormad3acencies <his is done or reasons o e5cienc%



8

()P* Design

Eac# router connects to t#e ackone calle! area /( or t#e ackone area.

Routers t#at connect ot#er areas to t#e ackone &it#in an AS are calle! Area Bor!er Routers*ABRs+. 0ne inter'ace )ust e in area /.

0SP runs insi!e an autono)ous syste)( ut can also connect )ulti%le autono)ous syste)stoget#er. $#e router t#at connects t#ese ASes toget#er is calle! an Autono)ous Syste)

Boun!ary Router *ASBR+.



()P* =reas

=n ()P* area is a grouping o contiguousnetwor's and routers

)hare a common area ID

= router can be a member o more than one area"area border router#

=ll routers in the same area have the sametopolog% database

Bhen multiple areas exist there must alwa%s bean area @ "the bac'bone# to which other areasconnect



;

Bh% areasG

Decreases routing overhead7ompare to multiple smaller broadcast

domains instead o one large one

)peeds convergence

7on2nes networ' instabilit% "e.g. route Happing#to single area o the networ'

=dds considerabl% to the complexit% o setting up()P*



Area $er)inology



A

&)=9s in =rea

• &)=s communicate with ad3acent routers in thesame ()P* area

• )ubse0uentl% a change in a lin' state is

Hooded to all area routers via &)=s

• In larger networ's multiple areas ma% be created – &)=s are sent onl% to ad3acent routers in the

same area – =rea border routers connect areas passing

summari,ed route inormation between





61

Path 7alculation

7hanges to the topological database o a routertrigger a recalculation to re-establish the bestroute"s# to 'nown networ's

/ses the )P* "shortest path 2rst# algorithm

developed b% a computer scientist namedDi3'stra

<his is done b% each individual router using itsdetailed 'nowledge o the whole networ'

&eads to rapid and accurate convergenceCased on detailed 'nowledge o ever% lin' in

the area and the ()P* cost o each

builds an OSPF tree with itsel at the route



6

<%pes o eighbors

• ()P* can be de2ned or three t%pe oneighbors – Croadcast 4ulti =ccess "C4=# ex- Ethernet

–

Point to Point – on-Croadcast 4ulti =ccess "C4=#



66

()P* etwor' <%pes



6?

=d3acencies

Point to Point all routers orm ad3acencies

C4= C4= one router is elected as DR

DR establish ad3acenc% with ever% neighborrouter

&)= updates are exchanged onl% to DR

DR is the router which has highest priorit%

=ll 7I)7( routers has priorit% 1

I priorit% is same then router id is seen

<he RID is highest IP address o all interaces



68

Point-to-Point Links

/suall% a serial interace running either PPPor +D&7

o DR or CDR election re0uired

()P* autodetects this interace t%pe

()P* pac'ets are sent using multicast ?.@[email protected]=ll routers orm ad3acencies

1ulti-access Broa!cast



6

1ulti-access Broa!cast"et&ork

• $enerall% &= technologies li'e Ethernet and <o'en Ring

• DR and CDR selection re0uired

• =ll neighbor routers orm ull ad3acencies with the DR and CDR onl%

• Pac'ets to the DR use ?.@.@.

• Pac'ets rom DR to all other routers use ?.@[email protected]



6;

Electing t#e DR an! BDR

+ello pac'ets are exchanged via IP multicast.

<he router with the highest priorit% isselected as the DR.

I Priorit% is same then Router ID is seen

/se the ()P* router ID as the tie brea'er.



6

<erminolog%: DRs and CDRs

<hedesignatedrouter "DR# is

responsibleorgenerating&)=s onbehal o all

routersconnectedto the samesegment



6A

DR Responsibilit%

Bhen a router sees a new or changed lin'-stateit sends an &)= to its DR using a particularmulticast address

<he DR then orwards the &)= to all the otherrouters with whom it is ad3acent

4inimi,es the number o ormal ad3acenciesthat must be ormed and thereore the amount

o &)/ "lin' state update# pac'et tra5c in amulti-router networ'



?@

()P* )ummar%

=D -1@@

+op count is unlimited

7lassless !&)4

&oad balance up to )IJ routers Re0uire more processing power



?1

Casic ()P* 7on2guration

Router(config)# router ospf 1 <he number 1 in this example is a process-id #

that begins an ()P* process in the router4ore than one process can be launched in a

router but this is rarel% necessar%/suall% the same process-id is used throughoutthe entire networ' but this is not re0uired

<he process-id K can actuall% be an% valuerom 1 to ver% large integerL

<he process-id K cannot be MER( <his is (< the same as the =)K used in I$RP

and EI$RP



?

7on2guring ()P* =reas

=ter identi%ing the ()P* process %ou need to identi% theinteraces that %ou want to activate ()P* communications

&abN=Kcon2g t

&abN="con2g#Krouter osp 1

&abN="con2g-router#Knetwor' 1@.@.@.@ @.88.88.88

area GO@-?A?A;A8 ()P* area ID as a decimal value

=.C.7.D ()P* area ID in IP address ormat

&abN="con2g-router#Knetwor' 1@.@.@.@ @.88.88.88

area @

• Ever% ()P* networ' must have an area @ "the bac'bone area# towhich other areas connect )o in a multiple area networ' there must be an area @ <he wildcard mas' represents the set o hosts supported b%

the networ' and is reall% 3ust the inverse o the subnet mas'.



0SP states



??

()P* 7on2guration

• ()P* Process ID number is irrelevant. It can be the same onever% router on the networ'

• <he arguments o the networ' command are the networ'number "1@.@.@.@# and the wildcard mas' "@.88.88.88#

• Bildcards - = @ octet in the wildcard mas' indicates that thecorresponding octet in the networ' must match exactl%

• = 88 indicates that %ou don9t care what the correspondingoctet is in the networ' number

• = networ' and wildcard mas' combination o 1.1.1.1 @.@.@.@

would match 1.1.1.1 onl% and nothing else.• <he networ' and wildcard mas' combination o 1.1.@.@

@[email protected] would match an%thing in the range 1.1.@[email protected]



?8

()P* 7on2guration -1

R2

R3 R4

S/ S3

E/

S/

E/

S/

3/././.3

2/././.3

2/././.2 4/././.3

4/././.2

5/././

.3

3/././.25/././.2

= C



?

()P* 7on2guration -1

R2

R3 R4

S/ S3

E/

S/

E/

S/

3/././.3 2/././.3

2/././.2 4/././.3

4/././.2

5/././

.3

3/././.25/././.2

R1Kcong tEnter con2guration commands one per line. End with 7<&>M.

R1"con2g#Krouter os%' 3R1"con2g-router#Knet&ork 3/./././ /.266.266.266 area /R1"con2g-router#Knet&ork 2/./././ /.266.266.266 area / R1"con2g-router#K78

= C



?;

()P* 7on2guration -

R2

R3 R4

S/ S3

E/

S/

E/

S/

2//././.392;

2//././.;4/2//././.324/

2//././.422<

= C



?

()P* 7on2guration -

R2

R3 R4

S/ S3

E/

S/

E/

S/

2//././.3<

2//././.=

2//././.3/ 2//././.34

2//././.3

5

2//././.4

4

2//././.3; 2//././.45266.266.266.2

5/

266.266.266.2

62

266.266.266.2

62

266.266.266.2

25

= C



?A

()P* 7on2guration -

R2

R3 R4

S/ S3

E/

S/

E/

S/

2//././.3<

2//././.=

2//././.3/ 2//././.34

2//././.3

5

2//././.4

4

2//././.3; 2//././.45266.266.266.2

5/

266.266.266.2

62

266.266.266.2

62

266.266.266.2

25

R1Kcong tEnter con2guration commands one per line. End with7<&>M.R1"con2g#Krouter os%' 3R1"con2g-router#Knet&ork 2//././.39 /././.36 area/R1"con2g-router#Knet&ork 2//././. ; /././.4 area/ R1"con2g-router#K78

= C

R6Kcong tEnter con2guration commands one per line. End with7<&>M.R6"con2g#Krouter os%' 3R6"con2g-router#Knet&ork 2//././. 42 /././.43 area/R6"con2g-router#Knet&ork 2//././. 32 /././.4area / R6"con2g-router#K78

()P* d & b '



8@

()P* and &oopbac'Interaces

7on2guring loopbac' interaces when using the ()P*routing protocol is important

7isco suggests using them whenever %ou con2gure ()P*on a router

Loopback interfaces are logical interaces which are virtualsotware-onl% interaces the% are not real router interaces

/sing loopbac' interaces with %our ()P* con2gurationensures that an interace is alwa%s active or ()P*processes.

<he highest IP address on a router will become that router9sRID

<he RID is used to advertise the routes as well as elect theDR and CDR.

I %ou con2gure serial interace o %our router with highestIP =ddress this =ddress becomes RID o t is the RID o therouter because e router

I this interace goes down then a re-election must occur It can have an big impact when the above lin' is Happing



81

7on2guring &oopbac' Interaces

R1Kcong t

Enter con2guration commands one per line.End with 7<&>M.

R1"con2g#Kint loo%ack /R1"con2g-i#Ki% a!!ress 3<2.39.3/.3

266.266.266.266

R1"con2g-i#Kno s#utR1"con2g-i#K78

R1K



8

show ip protocolsshow ip protocols

Router#

•Veries t#e congure! ,P routing%rotocol %rocesses( %ara)eters an!

statistics

!eri%ing ()P* (peration

show ip route ospfshow ip route ospf

Router#

• Dis%lays all 0SP routes learne! y t#e

routershow ip ospf interfaceshow ip ospf interface

Router#

• Dis%lays t#e 0SP router ,D( area ,D an!a!>acency in'or)ation

!eri%ing ()P* (peration



86

show ip ospfshow ip ospf

Router#

• Dis%lays t#e 0SP router ,D( ti)ers( an!statistics

!eri%ing ()P* (peration"7ont.#

show ip ospf neighbor [detail]show ip ospf neighbor [detail]

Router#

• Dis%lays in'or)ation aout t#e 0SPneig#ors( inclu!ing Designate! Router*DR+ an! Backu% Designate! Router*BDR+ in'or)ation on roa!cast net&orks

h h i



8?

<he show ip route osp7ommand

RouterA# show ip route ospf

Codes: C - connected, - static, ! - !"R, R - R!, $ - %obile,

& - &", ' - !"R, - !"R e*ternal, + - +,!A - + inter area, 1 - + e*ternal tpe 1,

. - + e*ternal tpe ., - ", i - !-!, /1 - !-!

le0el-1, /. - !-! le0el-., - candidate default

"atewa of last resort is not set

12323232 .443.443.4432 is subnetted, . subnets

+ 123.3132 [112512] 0ia 12367323., 22:22:42, thernet2

<h h i i t



88

<he show ip osp interace7ommand

RouterA# show ip ospf interface e2

thernet2 is up, line protocol is up

!nternet Address 1236732315.7, Area 2

rocess !' 1, Router !' 123673231, 8etwor9 pe &R+A'CA, Cost: 12

rans%it 'ela is 1 sec, tate 'R+;R, riorit 1

'esignated Router (!') 12367323., !nterface address 12367323.

&ac9up 'esignated router (!') 123673231, !nterface address 123673231

i%er inter0als configured, ;ello 12, 'ead 72, <ait 72, Retrans%it 4

;ello due in 22:22:27

8eighbor Count is 1, Ad=acent neighbor count is 1

Ad=acent with neighbor 12367323. ('esignated Router)

uppress hello for 2 neighbor(s)



8

<he show ip osp neighbor 7ommand

Router&# show ip ospf neighbor

8eighbor !' ri tate 'ead i%e Address !nterface

123673131 1 >//5&'R 22:22:?1 123673131 thernet2

123.3131 1 >//5- 22:22:?@ 123.3131 erial2

show ip osp neighbor detail



8;

show ip osp neighbor detail

show ip osp database

) i P i i DR El i



)etting Priorit% or DR Election

ip ospf priorit number ip ospf priorit number

<his interace con2guration command assigns the()P* priorit% to an interace.DiSerent interaces on a router ma% be assigned

diSerent values. <he deault priorit% is 1. <he range is rom @ to 88.@ means the router is a DR(<+ER it can9t be the DR

or CDR.

Router(config-if)#

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Dynamic Routings Cisco