Goal
Check for presence of route 10.100.1.1/32 via peer with AS 4049.
If present, apply route map 60_30_ACCEPT_10_100. This will limit advertisements to peer 172.31.1.1 to strictly 10.100.0.0/8.
Prefix lists
config router prefix-list edit "match_10.100.1.1_32" config rule edit 1 set prefix 10.100.1.1 255.255.255.255 unset ge unset le next edit "accept_10.100/16" config rule edit 1 set prefix 10.100.0.0 255.255.0.0 set ge 24 // Also accept prefixes with a bitmask greater than 24, i.e /32 unset le next end
AS-path list
config router aspath-list edit "match-as-4049" config rule edit 1 set action permit set regexp "_4049_" next end next end
Route maps
config router route-map edit "match-from-AS-4049" config rule edit 1 set match-as-path "match-as-4049" set match-ip-address "match_10.100.1.1_32" next end next edit "60_30_ACCEPT_10_100" config rule edit 1 set match-ip-address "accept_10.100/16" next edit 2 set action deny next end next
BGP configuration
config router bgp config neighbour edit "172.31.1.1" set remote-as 64333 config conditional-advertise edit "60_30_ACCEPT_10_100" // route map to apply set condition-routemap "match-from-AS-4049" next end next
Neighbour output – no match
BGP neighbor is 172.31.1.1, remote AS 64333, local AS 65531, external link
13 accepted prefixes
21 announced prefixes
Conditional advertise-map:
Adv-map 60_30_ACCEPT_10_100root, cond-map match-from-AS-4049root, cond-state 1-0
Neighbour output – match
BGP neighbor is 172.31.1.1, remote AS 64333, local AS 65531, external link 13 accepted prefixes 5455 announced prefixes Conditional advertise-map: Adv-map 60_30_ACCEPT_10_100root, cond-map match-from-AS-4049root, cond-state 1-1
1-0 means condition was not met; 1-1 means it was.
To soft-clear outbound routes
exe router clear bgp ip 1.1.1.1 soft out
Fortinet musings 