Figure 19: Advertising A Route When Another Route Is Absent - Juniper JUNOSE SOFTWARE FOR E SERIES 11.0.X - BGP AND MPLS CONFIGURATION GUIDE 2009-12-30 Configuration Manual

JUNOSe 11.0.x BGP and MPLS Configuration Guide
advertises neither of the routes to router R2. Consequently, router R2 advertises both
10.10.20.0/24 and 10.10.30.0/24 to peergroup1.

Figure 19: Advertising a Route When Another Route is Absent

The following commands configure router R2:
68
Advertising Routes
host1(config)#router bgp 200
host1(config-router)#neighbor peergroup1 peer-group
host1(config-router)#neighbor peergroup1 remote-as 100
host1(config-router)#neighbor 10.6.6.2 peer-group peergroup1
host1(config-router)#neighbor 10.7.3.2 peer-group peergroup1
host1(config-router)#neighbor 10.4.4.2 peer-group peergroup1
host1(config-router)#neighbor peergroup1 advertise-map advertisetoPG1
non-exist-map condition1 sequence 5
host1(config-router)#neighbor peer-group1 advertise-map alternatetoPG1
non-exist-map condition2
host1(config-router)#exit
host1(config)#ip as-path access-list 1 permit ^300
!
!Configure route map to send one route to peergroup1
!
host1(config)#access-list 77 permit 10.10.30.0 0.0.0.255
host1(config)#route-map advertisetoPG1 permit 10
host1(config-route-map)#match ip address 77
host1(config-route-map)#exit
!
!Configure route map to match one trigger route
!
host1(config)#access-list 70 permit 172.24.20.0 0.0.0.255
host1(config)#route-map condition1 permit 10
host1(config-route-map)#match ip address 70
host1(config-route-map)#exit
!
!Configure route map to send alternate route to peergroup1
!
host1(config)#access-list allow permit 10.10.20.0 0.0.0.255