Advertising A Route Only When Another Route Is Present; Figure 18: Advertising A Route When Another Route Is Present - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

JUNOSe 11.1.x BGP and MPLS Configuration Guide

Advertising a Route Only When Another Route is Present

You can use the exist-map keyword with the neighbor advertise-map command to
advertise a route only when the routing table contains some other particular route.
In the network shown in Figure 18 on page 66, router 2 (R2) has established BGP
sessions with both router 1 (R1) and router 3 (R3). The plan is for router 2 to send
router 1 an advertisement for the route to prefix 10.10.20.0/24 only if router 2 has
received a route to prefix 172.24.19.0/24 from router 3.
Alternatively, if the route to prefix 172.24.20.0 has been installed in the BGP routing
table on router 2, then router 2 advertises to router 1 the route to prefix 10.10.30.0.
In this case, the route does not have to be learned from router 3.

Figure 18: Advertising a Route When Another Route is Present

The following commands represent a partial configuration of router R2:
66
Advertising Routes
host1(config-router-af)#neighbor 192.168.2.2 advertise-map advertiseroutes
exist-map matchroute sequence 10
Use the no version to remove the conditions set for advertising to the peer or
peer group the routes specified by the route map. Use the default version to
remove the explicit configuration from the peer or peer group and reestablish
inheritance of the feature configuration.
See neighbor advertise-map.
host1(config)#router bgp 200
host1(config-router)#address-family ipv4 unicast
host1(config-router-af)#neighbor 10.2.0.1 remote-as 100
host1(config-router-af)#neighbor 10.2.0.1 advertise-map advertisetoR1 exist-map
trigger1 sequence 10
host1(config-router-af)#neighbor 10.2.0.1 advertise-map alternatetoR1 exist-map
trigger2
host1(config-router-af)#exit
host1(config-router)#exit
!
!Configure route map to send one route to R1
!