Advertising Ipv4 Routes Between Ipv6 Bgp Peers; Advertising Routes Conditionally - Juniper JUNOSE 11.2.X BGP AND MPLS Configuration Manual

Advertising IPv4 Routes Between IPv6 BGP Peers

Advertising Routes Conditionally

Copyright © 2010, Juniper Networks, Inc.
When an IPv6 network connects two separate IPv4 networks, you can use IPv6 to
advertise the IPv4 routes over the BGP session, using TCP IPv6 as the transport
mechanism. Similarly, you can advertise IPv6 routes between two IPv4 peers over their
BGP session.
Configure the peers by using IPv6 addresses within the IPv4 unicast address family. You
can set the IPv4 next hop with a static route or by configuring an inbound or outbound
route map. This action overrides the IPv4 next hop that is advertised to the peer for IPv4
routes over BGP IPv6 peers.
If you do not use the route map, then the advertised IPv4 next hop is set to the BGP router
ID. That value generally makes the next hop unreachable by the other BGP IPv6 peer.
host1(config)#router bgp 100
host1(config-router)#neighbor 21:1 remote-as 200
host1(config-router)#route-map my-v4-nexthop
host1(config-router)#set ip next-hop 10.13.5.1
host1(config-router)#address-family ipv4 unicast
host1(config-router-af)#neighbor 21:1 activate
host1(config-router-af)#neighbor 21:1 route-map my-v4-nexthop out
By default, a BGP speaker advertises the best routes in its routing table to its peers.
However, in some circumstances, you might prefer that some routes be advertised to a
peer or peer group only when another route is in the BGP routing table, or only when that
route is not in the routing table. BGP conditional advertisement enables you to control
route advertisement without having to rely on only the best routes.
For example, in a multi-homed network, you might want to advertise certain prefixes to
one of the providers when a failure occurs in the peering session with a different provider,
or when there is only partial reachability to that peer.
In other cases, the advertisement to a peer of certain routes might be useful only in the
event that some other routes are present in the BGP routing table.
You can use the neighbor advertise-map command with route maps to configure
conditional advertisement of BGP routes to a peer or peer group within an address family.
BGP conditional advertisement does not create routes. The routes specified by the route
map in the neighbor advertise-map command must already be present in the BGP routing
table.
BGP conditional advertisement is supported in only the following address families:
Unicast IPv4
Unicast IPv6
Multicast IPv4
Multicast IPv6
Chapter 1: Configuring BGP Routing
63