FAQ
the problem occur when two routers connected via frame-relay switch (2522 router), the configuration on switch is correct as well as on both routers, the loop back interface has been made on RB router i.e RB has 20.0.0.0/8, while at RA router the static router is defined as
ip route 20.0.0.0 0.255.255.255 serial 0
it was not able to send packets to 20.0.0.0/8 when run debug, it got error like encapsulation failed, now when it replaced the static route with next hop ip it was working fine, why ????
When a layer3 packet is going to be sent out, the router must know the layer 2 header to encapsulate the Layer3 packet.In this case, it must know which dlci number (as well as other layer2 information) to encap the IP packet. If you only indicate a connected interface for the static route, and there are many dlci numbers on this interface, the router will not know which dlci number to use and thus gives you a encapsulation failure message.
On the other hand, if you indicate a next-hop address on the static route and there is a frame-relay map which maps a dlci number to this next-hop address , the router will know the exact dlci number to encapsulate the ip packet and the packet will be sent out successfully.
