PPP Host Routes

The output of the show ip route command might differ between PPP and HDLC encapsulations when IP unnumbered configuration is used on serial interfaces. PPP installs a host route to the IP address that is used on the serial interface at the other end as a directly connected network. If the same prefix is also learned through OSPF as in this configuration, it displays only as a connected route. This is because connected routes have a lower administrative distance than OSPF and are more preferred. You can change this behavior when you issue the "no peer neighbor-route" command under the serial interfaces which prevents a host route from being installed and treats it as an OSPF route.

This is not the case with HDLC because it does not install a host route. HDLC installs an OSPF route for the address on the other end when IP unnumbered is used.