Normally, the next hop is a directly connected network node. When IP unnumbered is configured, routes learned through the IP unnumbered interface have the interface as the next hop instead of the source address of the routing update. Thus we avoid an invalid next hop address problem due to the source of the routing update coming from a next hop that is not directly connected. Let's look at four different sample configurations for IP unnumbered. In the network diagram below, on either side of the serial link we have the same major net with different subnets.
Type escape sequence to abort.
171.68.178.196 Type escape sequence to abort. The route information about subnets is correctly maintained in this scenario. In the diagram below, on either side of the serial link we have different major nets and no subnets. In the diagram below, on one side of the serial link we have a major net with a subnet, and on the other side a major net with no subnet. Type escape sequence to abort.