CCNP Enterprise Core (350-401) Cisco Routing

BGP Loop Prevention

As BGP is a path vector routing protocol, it does not keep a complete map of the network topology.

BGP behaves like a distance vector protocol in ensuring that paths are loop free.

The well-known mandatory attribute, AS_PATH, includes a complete list of all the ASNs that the prefix advertisement has transmitted through up to that point. If a BGP router recieves an advertisement which contains its own ASN in the AS_PATH attribute, it will discard the routing advertisement due to the router thinking that the packet has already traversed through its network.

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