BGP Next-Hop Behavior
CCNP BSCI
[ 62 ] CCNP BSCI Quick Reference
AS 65100
AS 65200
AS 65300
10.2.2.1
10.2.2.2
10.3.3.1
10.3.3.2
10.3.3.3
RtrA RtrD
RtrB RtrC
BGP Next Hop on a Multiaccess Network
On a multi-access network, BGP can adjust the next-hop attribute to avoid an
extra hop. In Figure 6-3, RtrC and RtrD are EBGP peers, and RtrC is an
IBGP peer with RtrB. When C sends an update to D about network 10.2.2.0,
it normally gives its interface IP address as the next hop for D to use. But
because B, C, and D are all on the same multiaccess network, it is inefficient
for D to send traffic to C, and C to then send it on to B. This process unnecessarily
adds an extra hop to the path. So, by default, RtrC advertises a next
hop of 10.3.3.3 (RtrB’s interface) for the 10.2.2.0 network. This behavior can
also be adjusted with the neighbor [ip address] next-hop-self command.