BGP Aggreagation
- It's done only for subnets that are in the BGP table.
- The routing table must have at least 1 route more specific than the aggregate...
- The only way for BGP to install an aggregate is if at least ONE more specific route that is aggregated is in the routing table.
- You first need to enter the network statement before entering the aggregate statement.
IOS will install a route with the next hop Null0. That's why the routing table must have at least 1 route more specific than the aggregate.
router bgp 65109
bgp router-id 33.33.33.33
network 1.1.0.0 mask 255.255.255.0
network 1.1.1.0 mask 255.255.255.0
aggregate-address 1.1.0.0 255.255.254.0
This will advertise 1.1.0.0/24, 1.1.1.0/24, and 1.1.0.0/23 in the routing table. or
router bgp 65109
bgp router-id 33.33.33.33
network 1.1.0.0 mask 255.255.255.0
network 1.1.1.0 mask 255.255.255.0
aggregate-address 1.1.0.0 255.255.254.0 summary-only
This will advertise 1.1.0.0/23 only in the routing table. or
router bgp 65109
bgp router-id 33.33.33.33
network 1.1.0.0 mask 255.255.255.0
network 1.1.1.0 mask 255.255.255.0
aggregate-address 1.1.0.0 255.255.254.0 suppress-map abc
!
access-list 1 permit 1.1.1.0 0.0.0.255
!
route-map abc permit 10 match ip address 1
- This will suppress 1.1.1.0.
- This will advertise 1.1.0.0/24 and 1.1.0.0/23 (aggregate and 1 specific route) in the routing table.