IPv6 Route Determination Process

In step 2 of the preceding procedure, the host determines the next-hop address and nexthop interface by using its local routing table. The details of this process are as follows:

1. For each routing table entry, the first N bits in the route's network prefix are compared with the same bits in the destination address in the packet header, where N is the number of bits in the route's prefix length. If these bits match, the route is determined to be a match for the destination.
2. The list of all matching routes is compiled. If only one matching route is found, this route is chosen and the route determination process is ended.
3. If multiple matching routes are found, the matching route having the largest prefix length is chosen and the route determination process is ended.
4. If multiple matching routes having the largest prefix length are found, the matching route having the lowest metric is chosen and the route determination process is ended.
5. If multiple matching routes having the largest prefix length and lowest metric are found, one of these routes is selected and the route determination process is ended.

The effective result of this IPv6 route determination process is as follows:

1. If a route can be found that matches the entire destination address in the packet header, then the next-hop address and interface specified in this route are used to forward the packet.
2. If a route of the type described in step 1 is not found, the most efficient (that is, lowestmetric) route that has the longest prefix length matching the destination address is used to forward the packet.
3. If a route of the type described in step 2 is not found, the packet is forwarded using the default route (with network prefix ::/0).