iBGP Loop Prevention Mechanism

[haryortheyji]

I understand that AS_PATH is the loop prevention mechanism used between different ASs running BGP. My question is does iBGP have any loop prevention mechanism within the same AS?. From the search I have done so far, there were comments that iBGP uses split-horizon, which does not fit into the definition and use case of split-horizon; what I learn on an interface will not be advertised out the same interface. By default, internal BGP does not advertise what it learned from its iBGP neighbor to another iBGP neighbor.

[pman · Accepted solution]

Hi,

for iBGP full-mesh topology:

in a full mesh topology BGP uses a split horizon rule which won’t advertise ibgp routes to other ibgp peers

for iBGP non full-mesh topology:

In this case a route-reflector are applicable

     The following rules are used to detect and avoid routing loops caused by route reflection:

• If a router received an iBGP route with the Originator-ID attribute set to its own "router-id", the route is discarded.
• If a route reflector receives a route with a "cluster-list" attribute containing its "cluster-id", the route is discarded.