Iteration refers to the following process: BGP receives a route from the IBGP neighbor. Generally, the next hop of the route is the loopback address of the peer end. Actually, the information about such a next hop cannot guide traffic forwarding, and the information about the real next hop of the egress is needed.


Route iteration is classified into two types: route iteration based on the outbound interface and next hop, and tunnel iteration.


The iteration of the next hop for an egress indicates that the next hop learnt by BGP is searched for in the IP routing table. When a route (generally, an IGP route) with the actual next hop and egress information is found, the next hop and egress information is filled in the IP routing entry of this BGP route and generate the corresponding FIB entry.

The iteration of tunnels indicates that private routes are crossed in the VPN instance. In this case, the next hop is the loopback address of the remote PE and the egress information and OutGoingToken information are unavailable. In this case, this loopback address is unavailable. The system searches for related information and fills such information in the forwarding entry. The routing management module regards the next hop of the route as the destination address and checks the global tunnel list to determine whether the information about the tunnel to the destination address exists. If so, the module fills in the tunnel information in the routing entry and generates the corresponding FIB entry.

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