notes: BGP conditional Route Advertisement

BGP conditional route advertisement offers an alternative way to affect how traffic enters the AS.


ip prefix-list PREFIX-A permit 30.0.0.0/24 - Matches the advertised prefix
ip prefix-list LINK-300-200 permit 30.20.1.0/30 - Matches the watched prefix !
!

route-map ADV-MAP permit

match ip address prefix-list PREFIX-A - References the advertised prefix
!

route-map WATCH permit

match ip address prefix-list LINK-300-200 - References the watched prefix
!

router bgp 300

neighbor 100.1.1.1 advertise-map ADV-MAP non-exist-map WATCH - Applies conditional route advertisement for AS-100






verification:

sh ip bgp neighbors 100.1.1.1 | i Condition
> Condition-map WATCH, Advertise-map ADV-MAP, status: Advertise - A positive, the WATCH route is down

 sh ip bgp neighbors 100.1.1.1 | i Condition
> Condition-map WATCH, Advertise-map ADV-MAP, status: Withdraw - A negative, the WATCH route is up