BGP Next-Hop Processing

• BGP needs an IGP to perform route recursion.
• iBGP will not modify next hop as it advertises to its neighbor.
  • Can be modified with ‘neighbor <address> next-hop-self’
    • Update source IP is used as next hop.
  • Next hop can be modified using route map as well.
    • updates being received.
    • Configuration:
      • neighbor <address> route-map <name> in | out
      • Uses set clause

• Next hop self on edge router
  • Peer can use same next hop on outbound updates to iBGP peers.
  • Same dynamic update group
  • Don’t need to include external links to IGP.
  • cons
    • Hinders fast convergence of external uplink failure.

Changing ‘next hop self’ with route-map:

R8 and R10 are in AS810.1, iBGP peers, and R5 is an EBGP peer. R10 receives BGP routes from R5 via R8, but all next hops stay as is, the inbound IP address of 10.8.8.2 from R5. If R5 does not know how to reach that transit link, it will never add routes into its local RIB from R5. This can be changed with ‘next hop self’ in many ways, this is through a route map.

R8 will advertise next hop self via BGP through the route map method. Again, no functional difference between using the normal ‘next-hop-self’ under the global BGP config and this. Also- the next hop will look like whatever the ‘update source’ is setup as.