BGP Conditional Route Injection (CRI)

Will INJECT a route based on a condition 
Conditional Route Injection (CRI) is special feature that allows a BGP speaker to “de-aggregate” a particular prefix, CRI operation is the opposite of aggregation, and its purpose is to create specific prefixes at the administrator’s discretion.

R5(config-router)#aggregate-address 10.0.0.0 255.255.252.0 summary-only
Aggregating the address on R5 we can only see the route of 10.0.0.0/22 in the R4 BGP table

Now we will create prefix-list matching ip address of 10.0.0.0/24 and 10.0.1.0/24 on R2 and de-aggregate them so that R4 learns these IP perfixes from R2

R2#
!
router bgp 123
 no synchronization
 bgp log-neighbor-changes
 bgp inject-map INJECT-ROUTE exist-map AGGREGATE-EXIST
 network 2.2.2.0 mask 255.255.255.0
 neighbor 12.1.1.1 remote-as 123
 neighbor 12.1.1.1 next-hop-self
 neighbor 24.1.1.4 remote-as 400
 neighbor 24.1.1.4 send-community
 no auto-summary
!
ip prefix-list AGGREDATE-ADD seq 10 permit 10.0.0.0/22
!
ip prefix-list INJECT-ROUTE seq 10 permit 10.0.0.0/24
ip prefix-list INJECT-ROUTE seq 20 permit 10.0.1.0/24
!
ip prefix-list ISP1 seq 10 permit 12.1.1.1/32
!
route-map AGGREGATE-EXIST permit 10
 match ip address prefix-list AGGREDATE-ADD
 match ip route-source prefix-list ISP1
!
route-map INJECT-ROUTE permit 10
 set ip address prefix-list INJECT-ROUTE


we can see the IP perfixes on R4