Why Disable Peer Neighbor Route
When configure PPP over Frame Relay, we may observe that there are 32bit host route in both PPP link router, along with one 24bit subnet route. So, what’s the purpose of host route in PPP link? The peer neighbour route is used to provide reachability when both ends of the PPP link are not on the same logical subnet, or IP unnumbered. For example, on Router A, the interface virtual-template 1 IP is 10.10.10.1/24, on Router B, the interface virtual-template 1 IP is 192.168.100.1/24. Then, when PPP Link is up, Router A can ping Router B by using different subnet IP address successfully. However, if two Virtual-Template interface are in the same subnet, then we don’t need host route generated. So, we can safely disable by “no peer neighbour-route” command under Virtual-Template interface.
Before disable, the routing table are as following:
Router A:
C 10.10.24.0/24 is directly connected, Virtual-Access2
C 10.10.24.4/32 is directly connected, Virtual-Access2
Router B:
C 10.10.24.0/24 is directly connected, Virtual-Access2
C 10.10.24.2/32 is directly connected, Virtual-Access2
After disable peer neighbour route, the routing table are as following:
Router A:
C 10.10.24.0/24 is directly connected, Virtual-Access2
Router B:
C 10.10.24.0/24 is directly connected, Virtual-Access2
Also, recall that how router does when forward a packet.
- Router look up the destination IP address and search on routing table by longest-matching approach.
- Router do Layer3 to Layer2 map searching for Ethernet or Frame Relay to get layer2 address, either MAC or DLCI, but not for PPP.
- Router finally encapsulate the package and send out the interface in the forwarding table.
Can IPv6 do ppp peer neighbor-route also?
I mean, what if the scenario is that the frame-relay interface is unnumbered (therefore have to use ppp virtual-template)?
What can we do to make this work, because as far as i have tested, ppp peer neighbor-route doesn’t work with ipv6.
Thanks!
Interesting question. I guess we don’t need peer neighbour route for IPv6 because when IPv6 is enabled, there is a link local address FE80::. We need to issue “no ipv6 nd ra suppress” command under interface Virtual-Template, so that router can advertise route to the neighbor. For IPv4, because when router handle layer 3 to layer 2 translation, it cannot refer to ARP (for Ethernet) or DLCI (for Frame Relay). So the best way let the router know the other end of PPP is to have a peer neighbour route in local route table.
However, I have encountered another problem. Do you know why Virtual-Template interface cannot copy/clone ipv6 address to Virtual-Access interface? It works for IPv4 address.