IP next-hop peer address (BGP)

In BGP routing protocol, the update from the external AS will contains the next hop address of the external hop itself. Therefore, when the router receives the update from the external AS and advertises the update to the other routers via iBGP, the other routers will see the next hop of the advertised networks via the external router IP address.  However, we can use the next-hop-self command in the BGP process at the Border router to fix the problem. But what if we cannot use the next-hop-self command? Do we have any other option?

Yes. We can use the route-map and set ip next-hop peer-address command to tell the iBGP learn router to forward the packet to its peer address instead of the external router IP address. Check the example below for more detailed explanation.

In this example, R1 advertise 10.10.10.0/24 network to R2. R2 advertises this network to R3 via BGP. However, R2 does not have the next-hop-self command configured which makes the R3 consider the R1 as the next hop address. The problem is R3 does not know how to get to R1. Therefore, R3 does not have reachability through the 10.10.10.0/24 network.


R2
router bgp 200
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.168.1.1 remote-as 100
 neighbor 192.168.2.2 remote-as 200

R3

R3#sh ip bgp
BGP table version is 2, local router ID is 192.168.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*>i10.10.10.0/24    192.168.1.1              0    100      0 100 i
R3#

We use the next-hop peer address command in the R2 which makes R3 forward the packet destined to 10.10.10.0/24 network via its peer address which in this case is R2 address.

R2

router bgp 200
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.168.1.1 remote-as 100
 neighbor 192.168.2.2 remote-as 200
 neighbor 192.168.2.2 route-map PEER-ADDRESS out

route-map PEER-ADDRESS permit 10
 set ip next-hop peer-address
!

R3

R3#sh ip bgp

BGP table version is 2, local router ID is 192.168.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

*>i10.10.10.0/24    192.168.2.1              0    100      0 100 i

R3#

Now R3 see the next hop address via R2. We can test the connectivity through this network now.

R3#ping 10.10.10.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.10.10.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 4/34/108 ms

R3#