8-17 neighbor ip-address peer-group-name next-hop-self

8-17 neighbor { ip-address peer- group - name } next -hop-self

Syntax Description:

• ip-address Neighbor's IP address.

• peer-group-name Name of the peer group. See section 8-19.

Purpose: When a BGP router learns routes via EBGP, and those routes are advertised to an IBGP neighbor, the next-hop information is sent unchanged. This command allows a BGP router to change the next-hop information that is sent to IBGP peers. The next-hop information is set to the IP address of the interface used to communicate with the neighbor.

Cisco IOS Software Release: 10.0. Peer group support was added in Release 11.0.

Configuration Example: Setting Next-Hop Information for Advertised Prefixes

Every prefix that is advertised using BGP contains next-hop information. Figure 8-15 shows the next-hop behavior for EBGP and IBGP. The advertisement for network 198.16.1.0/24 from Router B to Router A contains a next hop of 172.16.1.1. EBGP next-hop information is preserved when the prefix is advertised via IBGP. Router B advertises network 198.16.1.0/24 to Router C, with the next-hop information received from Router A.

Figure 8-15. Next Hop for EBGP and IBGP Connections

On a multiaccess network, such as Ethernet or Token Ring, the next-hop behavior is as shown in Figure 8-16. Router B learns about network 198.16.1.0/24 from Router A via IGP. Router B advertises 198.16.1.0/24 to Router C via EBGP with the next-hop information set to the address of Router A. This is done to avoid the extra hop of sending packets destined to network 198.16.1.0/24 to Router B.

Figure 8-16. Next Hop for Multiaccess Networks

The next-hop behavior for a nonbroadcast multiaccess (NBMA) network is similar to that of a multiaccess network. Figure 8-17 shows a partially meshed NBMA network using a hub-and-spoke configuration. PVCs have been configured between the hub (Router B) and the spokes (Routers A and C). There is no PVC from Router A to C. Both PVCs are assigned to the same IP subnet, 172.16.1.0/24. Because the PVCs are on the same IP subnet, Router B sets the next-hop information for 198.16.1.0/24 to 172.16.1.1 when sending an update to Router C. Because Router C does not have a PVC to Router A, routing for this network will fail. In this situation, Router B needs to set the next hop for 198.16.1.0/24 to 172.16.1.2, as shown in the following configuration:

Figure 8-17. Next Hop for NBMA Networks

 Router B  router bgp 1   neighbor 172.16.1.3 remote-as 2   neighbor 172.16.1.3 next-hop-self  

Verification

Verify the next hop for network 198.16.1.0/24 on Router C by using the show ip bgp command on Router C:

 rtrC#  show ip bgp  BGP table version is 22, local router ID is 172.16.1.13 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path  *> 198.16.1.0/24    172.16.1.2                 0             0 2 i  

Troubleshooting

1. Verify that the BGP neighbors are in the Established state using the show ip bgp neighbors command.

   If the neighbor relationship is not in the Established state, see section 8-23.

2. Verify the next-hop setting using show ip bgp.