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1 - 11 CCNP: Building Scalable Internetworks v5.0 - Lab 6-1 Copyright 2006, Cisco Systems, Inc

Lab 6-1 Conf igur ing BGP with Default Routing

Topology Diagram

Learning Objective

In this lab, you will configure BGP to exchange routing information with twoInternet Service Providers (ISPs).

Scenario

The International Travel Agency relies extensively on the Internet for sales. Thecompany has contracted with two ISPs for Internet connectivity with faulttolerance. You need to configure BGP, which runs between the San Joseboundary router and the two ISP routers.

Step 1: Assign IP Addresses

Configure the network according to the diagram, but do not configure a routingprotocol. Configure a loopback interface with an IP address for each ISP routeshown in the diagram. These loopbacks simulate real networks that can bereached through the ISP. Configure two loopback interfaces with the IPaddresses for the San Jose router. These loopbacks simulate the connectionsbetween the core routers.

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Use ping to test the connectivity between the directly connected routers.Note that router ISP1 cannot reach router ISP2.

Step 2: Configure the ISPs

Configure the ISP routers, and the International Travel Agencys boundary router,

San Jose. On the ISP1 router, enter the following configuration:

I SP1( conf i g) #r out er bgp 200I SP1( conf i g- r out er) #nei ghbor 10. 0. 0. 2 r emote- as 100I SP1( conf i g- r out er) #network 12. 0. 1. 0 mask 255. 255. 255. 0

On ISP2, configure BGP:

I SP2( conf i g) #r out er bgp 300I SP2( conf i g- r out er) #nei ghbor 172. 16. 0. 2 r emote- as 100I SP2( conf i g- r out er) #network 172. 16. 1. 0 mask 255. 255. 255. 0

Step 3: Conf igure SanJose BGP

Configure the San Jose router to run BGP with both providers:

SanJ ose(conf i g)#r out er bgp 100SanJ ose( conf i g- r out er) #nei ghbor 10. 0. 0. 1 r emote- as 200SanJ ose( conf i g- r out er) #nei ghbor 172. 16. 0. 1 r emote- as 300SanJ ose( conf i g- r out er) #network 192. 168. 0. 0SanJ ose( conf i g- r out er) #network 192. 168. 1. 0

To verify the configuration, check the routing table for SanJose with the show iproute command:

SanJ ose#show ip route

Gat eway of l ast r esor t i s not set

172. 16. 0. 0/ 16 i s var i abl y subnet t ed, 2 subnets, 2 masksC 172. 16. 0. 0/ 30 i s di r ect l y connect ed, Ser i al 0/ 0/ 1B 172. 16. 1. 0/ 24 [ 20/ 0] vi a 172. 16. 0. 1, 00: 00: 03

10. 0. 0. 0/ 30 i s subnet t ed, 1 subnetsC 10. 0. 0. 0 i s di r ectl y connected, Ser i al 0/ 0/ 0C 192. 168. 0. 0/ 24 i s di r ect l y connected, Loopback0

12. 0. 0. 0/ 24 i s subnet t ed, 1 subnetsB 12. 0. 1. 0 [ 20/ 0] vi a 10. 0. 0. 1, 00: 00: 42C 192. 168. 1. 0/ 24 i s di r ect l y connected, Loopback1

SanJose has routes to the loopback networks at each ISP router. Verify thatSanJose has connectivity to these networks by pinging each loopback addressfrom its console. One way to do this is to create your own TCL script. If these

pings are not successful, troubleshoot.

Step 4: Verify BGP on the SanJose Router

To verify the operation of SanJose, issue theshow ip bgp command:

SanJ ose#show ip bgpBGP tabl e ver si on i s 5, l ocal r out er I D i s 192. 168. 1. 1

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Step 5: Filter Routes

Check ISP2s routing table using theshow ip route command. ISP2 should havea route that belongs to ISP1, network 12.0.1.0.

If SanJose advertises a route belonging to ISP1, ISP2 installs that route in itstable. ISP2 might then attempt to route transit traffic through the InternationalTravel Agency. Configure the SanJose router so that it advertises onlyInternational Travel Agency networks 192.168.0.0 and 192.168.1.0 to bothproviders. On the SanJose router, configure the following access list:

SanJ ose( conf i g) #access- l i st 1 permi t 192. 168. 0. 0 0. 0. 1. 255

Then apply this access list as a route filter using the distribute-listkeyword withthe BGP neighborstatement:

SanJ ose(conf i g)#r out er bgp 100SanJ ose( conf i g- r out er ) #nei ghbor 10. 0. 0. 1 di st r i but e- l i st 1 outSanJ ose( conf i g- r out er ) #nei ghbor 172. 16. 0. 1 di st r i but e- l i st 1 out

After you configured the route filter, check the routing table for ISP2 again. Theroute to 12.0.1.0, ISP1, should still be in the table.

Return to SanJose and issue the clear ip bgp *command. Wait until the routersreach the Established state, which might take several moments, and thenrecheck the ISP2 routing table. The route to ISP1 should no longer be in therouting table.

The route to ISP2, network 172.16.1.0, should not be in the routing table forISP1.

Step 6: Configure the Primary and Backup Routes Using Floating Static RoutesNow that bidirectional communication has been established with each ISP viaBGP, it is time to configure the primary and backup routes. This can be done withfloating static routes or BGP.

To look at the floating static route method, issue the show ip routecommand onthe SanJose router:





Notice that there is no Gateway of Last Resort defined. This is a huge problem,because SanJose is the border router for the corporate network. Assume that

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ISP1 is the primary provider, and ISP2 acts as the backup. Configure staticroutes to reflect this policy:

SanJ ose( conf i g) #i p r out e 0. 0. 0. 0 0. 0. 0. 0 10. 0. 0. 1 210SanJ ose( conf i g) #i p r out e 0. 0. 0. 0 0. 0. 0. 0 172. 16. 0. 1 220

Now verify that a default route is defined using the show ip routecommand:Gateway of l ast r esor t i s 10. 0. 0. 1 t o network 0. 0. 0. 0



12. 0. 0. 0/ 24 i s subnet t ed, 1 subnetsB 12. 0. 1. 0 [ 20/ 0] vi a 10. 0. 0. 1, 00: 16: 39C 192. 168. 1. 0/ 24 i s di r ect l y connected, Loopback1S* 0. 0. 0. 0/ 0 [ 210/ 0] vi a 10. 0. 0. 1

Test this default route by creating an unadvertised loopback on the router forISP1:

I SP1#conf i g tI SP1( conf i g) #i nt l oopback 100I SP1( conf i g- i f ) #i p addr ess 210. 210. 210. 1 255. 255. 255. 0

Issue the clear ip bgp 10.0.0.1command to reestablish a conversation with the10.0.0.1 BGP speaker:

SanJ ose#clear ip bgp 10.0.0.1

Wait until the BGP conversation is reestablished with the 10.0.0.1 host.

Issue the show ip routecommand to insure that the newly added210.210.210.0 /24 network does not appear in the routing table:

SanJ ose#show ip route

Gateway of l ast r esor t i s 10. 0. 0. 1 t o network 0. 0. 0. 0



12. 0. 0. 0/ 24 i s subnet t ed, 1 subnets

B 12. 0. 1. 0 [ 20/ 0] vi a 10. 0. 0. 1, 00: 27: 45C 192. 168. 1. 0/ 24 i s di r ect l y connected, Loopback1S* 0. 0. 0. 0/ 0 [ 210/ 0] vi a 10. 0. 0. 1

Ping the 210.210.210.1 loopback interface originating from the 192.168.1.1SanJose interface:

SanJ ose#pingProtocol [ i p] :Target I P addr ess: 210.210.210.1

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Repeat count [ 5] :Dat agr am si ze [ 100] :Ti meout i n seconds [ 2] :Ext ended commands [ n] : ySour ce addr ess or i nt erf ace: 192.168.1.1Type of ser vi ce [ 0] :Set DF bi t i n I P header ? [ no] :

Val i dat e r epl y dat a? [no] :Dat a pat t ern [0xABCD] :Loose, St r i ct , Record, Ti mestamp, Verbose[none]:Sweep r ange of si zes [ n] :Type escape sequence t o abor t .Sendi ng 5, 100-byt e I CMP Echos t o 210. 210. 210. 1, t i meout i s 2 seconds:! ! ! ! !Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 32/ 32/ 36 ms

Step 7: Configure Primary and Backup Routes Using Static Routes

Another method for configuring primary and backup routes is to use the default-networkcommand instead of a 0.0.0.0/0 route.

Remove the floating static routes configured in Step 6:

SanJ ose( conf i g) #no i p r out e 0. 0. 0. 0 0. 0. 0. 0 10. 0. 0. 1 210SanJ ose( conf i g) #no i p rout e 0. 0. 0. 0 0. 0. 0. 0 172. 16. 0. 1 220

The network that was added in the last step, 210.210.210.0/24, should now beadvertised on the ISP1 router.

I SP1( conf i g) #r out er bgp 200I SP1( conf i g- r out er) #network 210. 210. 210. 0

I SP1#clear ip bgp 10.0.0.2

Configure the SanJose router a default-networkstatement to reestablish a

Gateway of Last Resort. Make sure that the classful network 210.210.210.0 /24appears in the routing table and is followed with the ip default-networkstatement:


B 210. 210. 210. 0/ 24 [ 20/ 0] vi a 10. 0. 0. 1, 00: 04: 51172. 16. 0. 0/ 16 i s var i abl y subnet t ed, 2 subnets, 2 masks

C 172. 16. 0. 0/ 30 i s di r ect l y connect ed, Ser i al 0/ 0/ 1B 172. 16. 1. 0/ 24 [ 20/ 0] vi a 172. 16. 0. 1, 00: 21: 19



SanJ ose( conf i g) #i p def aul t - network 210. 210. 210. 0

Wait a few moments, and then re-examine the routing table on SanJose:

Gateway of l ast r esor t i s 10. 0. 0. 1 to net work 210. 210. 210. 0

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B* 210. 210. 210. 0/ 24 [ 20/ 0] vi a 10. 0. 0. 1, 00: 04: 28172. 16. 0. 0/ 16 i s var i abl y subnet t ed, 2 subnets, 2 masks




This establishes ISP1 as the only default route. This route can be manipulatedwith policy routing. Correct this by adding a backup route to the 172.16.0.1 hoston ISP2:

SanJ ose( conf i g) #i p r out e 0. 0. 0. 0 0. 0. 0. 0 172. 16. 0. 1 220

EBGP learned routes have an administrative distance of 20 and are preferred toany routes with an administrative distance greater than 20, such as the defaultroute defined above with an administrative distance of 220. The default route

acts as a backup if the 210.210.210.0 /24 network is unavailable because of afault or misconfiguration, or during the short period after a clear ip bgp 10.0.0.1command is issued.

Verify that this newly added route establishes a consistent default route while theBGP conversation between SanJose and ISP1 reestablishes. Notice that therouting table includes two candidate default routes (*), only one of which is usedbecause of different administrative distances.

SanJ ose#show ip routeCodes: C - connected, S - st at i c, I - I GRP, R - RI P, M - mobi l e,B - BGP D - EI GRP, EX - EI GRP ext ernal , O - OSPF, I A - OSPF i nter area N1- OSPF NSSA external t ype 1, N2 - OSPF NSSA ext ernal

t ype 2 E1 - OSPF external t ype 1, E2 - OSPF ext ernal t ype 2,E - EGP i - I S- I S, L1 - I S- I S l evel - 1, L2 - I S- I S l evel - 2, i a - I S- I Si nt er area * - candi dat e def aul t , U - per - user st at i c rout e, o - ODR P -peri odi c downl oaded st ati c r out e

Gateway of l ast r esor t i s 10. 0. 0. 1 to net work 210. 210. 210. 0

B* 210. 210. 210. 0/ 24 [ 20/ 0] vi a 10. 0. 0. 1, 00: 19: 17172. 16. 0. 0/ 16 i s var i abl y subnet t ed, 2 subnets, 2 masks



12. 0. 0. 0/ 24 i s subnet t ed, 1 subnets

B 12. 0. 1. 0 [ 20/ 0] vi a 10. 0. 0. 1, 00: 19: 17C 192. 168. 1. 0/ 24 i s di r ect l y connected, Loopback1S* 0. 0. 0. 0/ 0 [ 220/ 0] vi a 172. 16. 0. 1

SanJ ose#clear ip bgp 10.0.0.1SanJ ose#show ip route

Gateway of l ast r esor t i s 172. 16. 0. 1 t o network 0. 0. 0. 0

172. 16. 0. 0/ 16 i s var i abl y subnet t ed, 2 subnets, 2 masksC 172. 16. 0. 0/ 30 i s di r ect l y connect ed, Ser i al 0/ 0/ 1

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B 172. 16. 1. 0/ 24 [ 20/ 0] vi a 172. 16. 0. 1, 00: 45: 3110. 0. 0. 0/ 30 i s subnet t ed, 1 subnets

C 10. 0. 0. 0 i s di r ectl y connected, Ser i al 0/ 0/ 0C 192. 168. 0. 0/ 24 i s di r ect l y connected, Loopback0C 192. 168. 1. 0/ 24 i s di r ect l y connected, Loopback1S* 0. 0. 0. 0/ 0 [ 220/ 0] vi a 172. 16. 0. 1

SanJ ose#show ip routeGateway of l ast r esor t i s 10. 0. 0. 1 to net work 210. 210. 210. 0B* 210. 210. 210. 0/ 24 [ 20/ 0] vi a 10. 0. 0. 1, 00: 01: 03



12. 0. 0. 0/ 24 i s subnet t ed, 1 subnetsB 12. 0. 1. 0 [ 20/ 0] vi a 10. 0. 0. 1, 00: 01: 03C 192. 168. 1. 0/ 24 i s di r ect l y connected, Loopback1S* 0. 0. 0. 0/ 0 [ 220/ 0] vi a 172. 16. 0. 1

As expected, while the BGP conversation was down between SanJose and ISP1,

the route to ISP2 was added as the Gateway of Last Resort. However, once BGPreestablished the conversation between SanJose and ISP1, the default route of210.210.210.0 was again set as the Gateway of Last Resort on SanJose.

Appendix A: TCL Verificat ion

I SP1#tclshI SP1( t c l )#I SP1( t cl ) #f oreach addr ess {+>12. 0. 1. 1+>192. 168. 0. 1+>192. 168. 1. 1+>172. 16. 1. 1+>10. 0. 0. 1+>10. 0. 0. 2

+>172. 16. 0. 1+>172. 16. 1. 1+>210. 210. 210. 1+>} {+>pi ng $addr ess }

Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 12. 0. 1. 1, t i meout i s 2 seconds:! ! ! ! !Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 1/ 1/ 1 ms


Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 192. 168. 1. 1, t i meout i s 2 seconds:! ! ! ! !

Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 28/ 28/ 28 msType escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 172. 16. 1. 1, t i meout i s 2 seconds:. . . . .Success r at e i s 0 percent ( 0/ 5)


Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 10. 0. 0. 2, t i meout i s 2 seconds:! ! ! ! !

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Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 28/ 28/ 32 msType escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 172. 16. 0. 1, t i meout i s 2 seconds:. . . . .Success r at e i s 0 percent ( 0/ 5)

Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 172. 16. 1. 1, t i meout i s 2 seconds:. . . . .

Success r at e i s 0 percent ( 0/ 5)Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 210. 210. 210. 1, t i meout i s 2 seconds:! ! ! ! !Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 1/ 1/ 4 msI SP1( t c l )#tclquit

SanJ ose#tclshSanJ ose(t cl ) #SanJ ose( t cl ) #f oreach addr ess {+>12. 0. 1. 1+>192. 168. 0. 1+>192. 168. 1. 1+>172. 16. 1. 1+>10. 0. 0. 1+>10. 0. 0. 2+>172. 16. 0. 1

+>172. 16. 1. 1+>210. 210. 210. 1+>} {+>pi ng $addr ess }








Type escape sequence t o abor t .

Sendi ng 5, 100- byt e I CMP Echos t o 172. 16. 1. 1, t i meout i s 2 seconds:! ! ! ! !Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 28/ 28/ 28 ms

Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 210. 210. 210. 1, t i meout i s 2 seconds:! ! ! ! !Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 28/ 28/ 32 msSanJ ose(t cl ) #tclquit

I SP2#tclshI SP2( t c l )#I SP2( t cl ) #f oreach addr ess {

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+>12. 0. 1. 1+>192. 168. 0. 1+>192. 168. 1. 1+>172. 16. 1. 1+>10. 0. 0. 1+>10. 0. 0. 2+>172. 16. 0. 1+>172. 16. 1. 1

+>210. 210. 210. 1+>} {+>pi ng $addr ess }

Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 12. 0. 1. 1, t i meout i s 2 seconds:. . . . .Success r at e i s 0 percent ( 0/ 5)



Type escape sequence t o abor t .

Sendi ng 5, 100- byt e I CMP Echos t o 172. 16. 1. 1, t i meout i s 2 seconds:! ! ! ! !Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 1/ 1/ 1 ms




Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 172. 16. 1. 1, t i meout i s 2 seconds:

! ! ! ! !Success r ate i s 100 percent ( 5/ 5) , r ound- t r i p mi n/ avg/ max = 1/ 1/ 1 ms

Type escape sequence t o abor t .Sendi ng 5, 100- byt e I CMP Echos t o 210. 210. 210. 1, t i meout i s 2 seconds:. . . . .Success r at e i s 0 percent ( 0/ 5)I SP2( t c l )#tclquit

Final Configurations

I SP1#show run!host name I SP1!i nter f ace Loopback0i p addr ess 12. 0. 1. 1 255. 255. 255. 0

!i nter f ace Loopback100i p addr ess 210. 210. 210. 1 255. 255. 255. 0

!i nterf ace Seri al 0/ 0/ 0i p address 10. 0. 0. 1 255. 255. 255. 252cl ock rat e 64000no shut down

!r out er bgp 200no synchr oni zati on

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net work 12. 0. 1. 0 mask 255. 255. 255. 0net work 210. 210. 210. 0nei ghbor 10. 0. 0. 2 remote- as 100no aut o- summar y

!end

SanJ ose#show run

!host name SanJ ose!i nter f ace Loopback0i p addr ess 192. 168. 0. 1 255. 255. 255. 0

!i nter f ace Loopback1i p addr ess 192. 168. 1. 1 255. 255. 255. 0

!i nterf ace Seri al 0/ 0/ 0i p address 10. 0. 0. 2 255. 255. 255. 252no shut down

!i nterf ace Seri al 0/ 0/ 1i p addr ess 172. 16. 0. 2 255. 255. 255. 252cl ock rat e 64000no shut down

!r out er bgp 100no synchr oni zati onnet work 192. 168. 0. 0net work 192. 168. 1. 0nei ghbor 10. 0. 0. 1 remote- as 200nei ghbor 10. 0. 0. 1 di str i but e- l i st 1 outnei ghbor 172. 16. 0. 1 r emot e- as 300nei ghbor 172. 16. 0. 1 di str i but e- l i st 1 outno aut o- summar y

!i p def aul t - net work 210. 210. 210. 0i p rout e 0. 0. 0. 0 0. 0. 0. 0 172. 16. 0. 1 220!access- l i st 1 per mi t 192. 168. 0. 0 0. 0. 1. 255!end

I SP2#show run!host name I SP2!i nter f ace Loopback0i p address 172. 16. 1. 1 255. 255. 255. 0

!i nterf ace Seri al 0/ 0/ 1i p addr ess 172. 16. 0. 1 255. 255. 255. 252no shut down

!r out er bgp 300no synchr oni zati onnet work 172. 16. 1. 0 mask 255. 255. 255. 0nei ghbor 172. 16. 0. 2 r emot e- as 100no aut o- summar y

!end

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