BGP - Conditional route injection

Topology

R5----R7

R5 is advertising 10.34.19.0/26 to R7
Configure R7 to inject 10.34.19.48/28

1) MAKE PREFIX-LISTS

ip prefix-list EXIST seq 5 permit 10.34.19.0/26
ip prefix-list INJECT 5 permit 10.34.19.48/28
ip prefix-list SOURCE seq 5 permit 192.168.5.5/32


2) MAKE ROUTE-MAPS

route-map INJECT permit 10
set ip address prefix-list INJECT

route-map EXIST permit 10
match ip address prefix-list EXIST
match ip route-source prefix-list SOURCE


3) CONFIGURE BGP

route bgp 567
bgp inject-map INJECT exist-map EXIST


4) VERIFY

R5#show ip bgp nei 192.168.7.7 advertised-routes | begin Net
Network Next Hop Metric LocPrf Weight Path
*> 10.34.19.0/26 192.168.2.2 0 200 0 24 1 i

R7#show ip bgp injected-paths | begin Net
Network Next Hop Metric LocPrf Weight Path
*>i10.34.19.48/28 192.168.5.5 0 200 0 24 1 i

Things to remember:

- Must use Prefix-lists, NOT ACLs
- Injected route must a subset of am aggregate already in the table
- Use "set" command for inject-map, not "match"
- I commonly forget the "prefix-list" argument when configuring the maps
- inject-map Command is a bgp command, not per-neighbor