IP Routing

Understanding Routing on NBMA interfaces (Frame Relay)

Routing over an NBMA interface follows the same address resolution concept as routing over Ethernet such that:
* When a static route points to an interface, L3 to L2 resolution is performed for the final destination.
* When a static route points to the next-hop value, L3 to L2 resolution is performed for the next-hop.

Here is an example that illustrates this concept:

R1, R2, and R3 are connected over Frame-Relay cloud.
R1 and R2 are connected via serial link.
  note: Serial point to point DOES NOT require
           L3 to L2 resolution. Why?
R1 and R2 has default route configured.
There is full reachability.
Inverse-ARP is enabled on all routers.



I have configured on R3 static routes as follows:

To prove my point:

I can ping R1s Loopback.

However, when I ping R2's Loopback (2.2.2.2), I an encapsulation failed.

Notice R3 doesn't have a frame-relay mapping for R2's Loopback0.  

To fix this, we would write a frame-map statement on R3 to tell it what PVC to use in order to get to 2.2.2.2:
R3 (config-if)# frame-relay map ip 1.1.1.1 302 

Now, I have the mapping:

Now, I am able to reach it: