ADTRAN AOS Version R10.1.0 Command Reference Manual page 2926

Command Reference Guide BGP AF Neighbor Command Set
point for the next AS. When the iBGP router receives packets destined for one of the external networks, it
performs a recursive lookup of the entries in its own IGP routing table to determine how to reach the BGP
next-hop address. Unless the iBGP router has a static route or an entry in its IGP routing table indicating
how to reach the edge router in the external AS, packets destined for those networks will be dropped. To
remedy this scenario, the iBGP peer must advertise its own IP address as the next-hop address to the
external networks. Consider the following example:
In external Border Gateway Protocol (eBGP), routes are normally advertised with a next hop set to the IP
address that the receiving peer has configured in its neighbor statement for this router. In the eBGP case
where the receiving router is in the same subnet as the current next hop, the current next hop is not
changed.
For broadcast multiaccess networks (Ethernet), this provides more efficient routing. For nonbroadcast
multiaccess (NBMA) networks, such as Frame Relay with a partial mesh using point-to-multipoint circuits,
this rule can cause significant problems. Since the partial mesh is on the same subnet, BGP applies the
rule of not changing the next-hop address, rendering routes in certain topologies invalid. This is one case
where this command is necessary to solve a problem.
Usage Examples
The following example enables next-hop-self for the IPv4 BGP AF neighbor on the default VRF instance:
(config)#router bgp 100
(config-bgp)#address-family ipv4
(config-bgp-ipv4)#neighbor 192.22.73.101
(config-bgp-ipv4-neighbor)#next-hop-self
The following example enables next-hop-self for the IPv4 BGP AF neighbor on the nondefault VRF
instance named RED1:
(config)#vrf RED1 route-distinguisher ip 192.17.250.24:33
(config)#router bgp 100
(config-bgp)#vrf RED1
(config-bgp-vrf)#address-family ipv4
(config-bgp-vrf-ipv4)#neighbor 10.20.1.1
(config-bgp-vrf-ipv4-neighbor)#next-hop-self
60000CRG0-35E Copyright © 2012 ADTRAN, Inc. 2926