Deaggregating with bgp inject-map

Hello

Let’s say we have an aggregate of 100.0.0.0/21 that we advertise somewhere in our network but we want to advertise also 100.0.1.0/24 to neighbor A, 100.0.2.0 to neighbor B and 100.0.3.0 to neighbor C at different places as best entry points.

We can do this with bgp inject-map.

 

(somewhere in network)

router bgp 100

aggregate-address 100.0.0.0 255.255.240.0 summary-only

network 100.0.0.0 mask 255.255.255.0

 

(near the edge to neighbor A)

router bgp 100

bgp inject-map INJECT exist-map EXIST

 

route-map INJECT permit 10

set ip address prefix-list PARTICULARNETWORK

<any additional parameters here”

route-map EXIST permit 10

match ip address prefix-list AGGREGATE

<any additional conditions here>

 

There is even a nice show command for this:

R7#show ip bgp injected-paths
BGP table version is 22, local router ID is 150.1.7.7
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i – IGP, e – EGP, ? – incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*> 10.0.1.0/24 155.1.37.3 0 i