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DES-7200 Configuration Guide Chapter 2 Configuring BGP IP VPN
2-40
DES-7200(config-router-af)#
neighbor rr-address
Activate
Enable the device to exchange VPN routes with
the RR in another AS.
DES-7200(config-router-af)#
neighbor rr-address
next-hop-unchanged
(Optional) Configure the device not to change the
next hop when advertising VPN routes to the
peer.
DES-7200(config-router)# show
running-config
View all configuration information.
Note
1. By default, the device modifies the next hop of a route as its own
address when advertising the route to an EBGP peer. Upon receipt of
the VPN route, the PE site in another AS considers the next hop of the
route as the RR. As a result, all inter-AS VPN traffic is transmitted
through the RR. This is generally not the optimal forwarding path and
has high requirements on the forwarding performance of the RR. To
avoid the preceding situation, you can run the neighbor
next-hop-unchanged command in the VPNv4 address family mode to
configure the device not to change the next hop of a VPNv4 route sent
to the BGP peer when you set up a multi-hop MP-EBGP session on the
RR.
2. The exchange of IPv4 routes is not required in a multi-hop MP-EBGP
session. At least the routes of the two addresses used to set up the
BGP session should be avoided. Otherwise, a PE has two routes to the
PE in another AS. One route is advertised by the ASBR in the local AS
and the other is by the multi-hop EBGP session. According to BGP
specifications, the EBGP route has a higher priority over the IGBP route
by default. As a result, the BGP module chooses the route advertised by
the multi-hop BGP and this results in the continued flapping of routes on
the PE to the PE in another AS. The VPN routes are thus not reachable.
# Configure an RR to set up a multi-hop MP-EBGP session with the RR in another AS.
DES-7200# configure terminal
DES-7200(config)# router bgp 1
DES-7200(config-router)# neighbor 30.30.30.2 remote-as 2
DES-7200(config-router)# neighbor 30.30.30.2 update-source loopback 0
DES-7200(config-router)# neighbor 30.30.30.2 ebgp-multihop
DES-7200(config-router)# address-family ipv4
DES-7200(config-router-af)# no neighbor 30.30.30.2 activate