Advertising Ipv4 Routes Between Ipv6 Bgp Peers; Advertising Routes Conditionally - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

bgp enforce-first-as

Advertising IPv4 Routes Between IPv6 BGP Peers

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.

Advertising Routes Conditionally

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
Use to cause BGP to determine whether the first AS in the AS path of a route
received from an EBGP peer matches the remote AS number of that peer.
If the AS does not match, BGP sends a notification to the peer with the error
code " update message error" and error subcode " malformed as-path."
This feature is disabled by default.
Example
host1(config-router)#bgp enforce-first-as
Causes BGP to check the AS path of all routes received after you issue the
command.
To apply the new behavior to routes that are already present in the BGP routing
table, you must use the clear ip bgp command to perform a soft clear or hard
clear of the current BGP session.
Use the no version to prevent the AS comparison from taking place.
See bgp enforce-first-as.
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
Chapter 1: Configuring BGP Routing
Advertising Routes
63