Aggregating While Suppressing Individual Routes

• Use the suppress-map keyword to suppress specified routes

Syntax:_

router(config-router)# aggregate-address address mask suppress-map route-map

Syntax:_

router(config-router)# aggregate-address address mask suppress-map route-map

© 2002, Cisco Systems, Inc. All lights reserved. Cisco CCIE Prep v1.0—Module 8-75

The form of the aggregate command that advertises the aggregate while suppressing only the more specific routes indicated by a route map is shown.

aggregate-address address address-mask suppress-map route-map-name

Look at the same scenario where two different AS systems are sending class B networks to a 3rd AS.

■ R1 is advertising the network 150.10.0.0/16 to R3.

■ R4 is advertising the network 150.40.0.0/16 to R3.

■ R3 has issued the following commands in its BGP configuration.

R3(config)# router bgp 300

R3(config-router)# aggregate-address 150.0.0.0 255.0.0.0 suppress-map SUPPRESSR4 R3(config-router)# exit

R3(config)# route-map SUPPRESSR4 permit 10 R3(config-route-map)# match ip address 4 R3(config-route-map)# exit

R3(config)# access-list 4 permit 150.40.0.0 0.0.255.255

The BGP table on R2 shows: R2#show ip bgp

BGP table version is 22, local router ID is 10.10.10.10

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete

Next Hop 172.16.23.3

Metric LocPrf Weight Path

0 300 i

172.16.23.3

0 300 100 I

You have received the aggregate and have suppressed the R4 more specific route (150.40.0.0) while allowing all other more specific routes (150.10.0.0). This option can be very confusing to understand. In this case, any addresses associated with a permit statement in the access list will be denied. To make it easier to understand, read the suppress-map statement and access list as follows: You are permitting network 150.40.0.0/16 to be suppressed while all other routes will not be suppressed. In other words, the implicit deny all at the end of the access list denies all other routes from being suppressed. Any routes that are denied from being suppressed are allowed into the BGP table.

Auto-Summary

* Auto-summarization on by default

• When auto-summarization is used, routes are summarized at classful boundaries

Syntax:

router(config-router)# auto-summary

k?« r

ASiOO^—

© 2002, Cisco Systems, Inc. All rights reserved. Cisco CCIE Prep v1.0—Module 8-

6

By default, BGP does not accept subnets redistributed from Interior Gateway Protocol (IGP). To advertise and carry subnet routes in BGP, use an explicit network command or the no auto-summary command. If you disable auto-summarization and have not entered a network command, you will not advertise network routes for networks with subnet routes unless they contain a summary route.

When you enable auto-summary, routes injected into BGP via redistribution are summarized at their classful boundary. Auto-summary does not apply to routes injected into BGP via the network command or through iBGP or external BGP (eBGP).

Auto-summary

Here is an example where R4 is redistributing static routes, connected routes, and routes learned via Enhanced Interior Gateway Routing Protocol (EIGRP) into BGP. Here is the R4 IP routing table.

R4# show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, 0 - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

El - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR

P - periodic downloaded static route

Gateway of last resort is not set

1.0.0.0/24 is subnetted, 1 subnets D 1.1.1.0 [90/2323456] via 172.16.70.3, 01:31:10, Ethernet0/0

2.0.0.0/24 is subnetted, 1 subnets D 2.2.2.0 [90/2323456] via 172.16.70.3, 01:31:10, Ethernet0/0

3.0.0.0/24 is subnetted, 1 subnets D 3.3.3.0 [90/409600] via 172.16.70.3, 01:31:10, Ethernet0/0

4.0.0.0/24 is subnetted, 1 subnets C 4.4.4.0 is directly connected, Loopback0

5.0.0.0/24 is subnetted, 1 subnets D 5.5.5.0 [90/2297856] via 172.16.45.5, 01:31:10, Serial0/1

6.0.0.0/24 is subnetted, 1 subnets D 6.6.6.0 [90/2809856] via 172.16.45.5, 01:31:11, Serial0/1

172.16.0.0/16 is variably subnetted, 6 subnets, 2 masks C 172.16.134.0/28 is directly connected, Serial0/0

D 172.16.56.0/24 [90/2681856] via 172.16.45.5, 01:31:11, Serial0/1

C 172.16.45.0/24 is directly connected, Serial0/1

D 172.16.23.0/24 [90/2195456] via 172.16.70.3, 01:31:11, Ethernet0/0

D 172.16.16.0/24 [90/2707456] via 172.16.70.3, 01:31:11, Ethernet0/0

C 172.16.70.0/24 is directly connected, Ethernet0/0

C 150.40.0.0/16 is directly connected, Loopback10

30.0.0.0/24 is subnetted, 1 subnets S 30.30.30.0 [1/0] via 150.40.0.2

Next, you redistribute EIGRP, connected, and static routes into R4's BGP. Here is R4's BGP table with the default of auto-summary enabled.

R4# show ip bgp

BGP table version is 32, local router ID is 4.4.4.4

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin

codes: i

- IGP,

, 1

e -

- EGP, ? -

incomplete

Network

Next

Hop

Metric LocPrf

Weight Path

*> 1.0.

0.

0

0 .

0

.0 .

0

250

32768 ?

*> 2.0.

0.

0

0 .

0

.0 .

0

250

32768 ?

*> 3.0.

0.

0

0 .

0

.0 .

0

250

32768 ?

*> 4.0.

0.

0

0 .

0

.0 .

0

0

32768 ?

*> 5.0.

0.

0

0 .

0

.0 .

0

250

32768 ?

*> 6.0.

0.

0

0 .

0

.0 .

0

250

32768 ?

*> 30.0

.0

.0

0 .

0

.0 .

0

250

32768 ?

*> 150.

40

.0.0

0 .

0

.0 .

0

0

32768 i

*> 172.

16

.0.0

0 .

0

.0 .

0

0

32768 ?

Notice that all routes have been summarized to their classful boundary. For instance, the 1.1.1.0/24 network in the IP routing table has been summarized to the classful network 1.0.0.0 in BGP.

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