Border Gateway Protocol - CCIE Routing and Switching Exam Certification Guide - page 434

aggregate-address Command

The command advertises an aggregate (summary) network if any more-

specific prefixes are present in the BGP table. A

aggregate-address

summary-only keyword suppresses

advertisements of the more-specific prefixes.

For example, if the BGP table has networks 100.100.4.0/24, 100.100.5.0/24, 100.100.6.0/24,
and 100.100.7.0/24, you can configure it to advertise an aggregate network of 100.100.4.0/22
and suppress the more specific networks. The commands are as follows:

router bgp 100
aggregate-address 100.100.4.0 255.255.252.0 summary-only

BGP Redistribution

Another method to advertise BGP routes is to import them into the BGP routing table through
redistribution of an IGP (such as OSPF and EIGRP). Both the command and redistri-

bution from an IGP add routes that are already in the IP table into the BGP table. You commonly
use this method in large enterprise internetworks with iBGP cores. Filtering selects the redis-
tributed prefixes and properly sets their attributes (especially origin). In Example 9-4, a route
map specifies attributes to some of the redistributed networks (on access list 40). Other redis-
tributed networks are specified in access list 50. You use the route map eigrp-to-bgp in the

network

redistribute statement sets local preference, origin, and weight

to redistributed routes that match access list 40. The second

command. The first route-map

route-map statement permits

routes that match access list 50 for redistribution.

Example 9-4

Redistribution of an IGP into BGP

router eigrp 111
network 15.0.0.0
!
router bgp 65511
no synchronization
redistribute eigrp 111 route-map eigrp-to-bgp
!
route-map eigrp-to-bgp permit 5
match ip address 40
set local-preference 200
set weight 10
set origin igp
!
route-map eigrp-to-bgp permit 10
match ip address 50
!
!
access-list 40 permit 15.186.0.0
access-list 40 permit 15.168.0.0

eigrp-to-bgp permit 5

eigrp-to-bgp permit 10