When to use “interface-dlci” or “map ip” on Frame Relay
by David Sudjiman ~ June 12th, 2009. Filed under: Cisco.I’ve done Frame-Relay IEWB a really long time ago yet I keep forgetting why I should use frame-relay interface-dlci or frame-relay map. Reading the Cisco IOS Wide-Area Networking Configuration Guide, Release 12.4T gives you the explanation and I decided to post it here to help me remember.
For point-to-point subinterfaces, the destination is presumed to be known and is identified or implied in the frame-relay interface-dlci command. For multipoint subinterfaces, the destinations can be dynamically resolved through the use of Frame Relay Inverse ARP or can be statically mapped through the use of the frame-relay map command.
We know that on Frame Relay relies on the mapping between DLCI to IP Address and this is done by using Inverse ARP. We also know that without using dynamic mapping, we can also use static mapping using command frame-relay interface-dlci or frame-relay map.
The different between the two is that frame-relay interface-dlci is used for point-to-point subinterfaces and frame-relay mapis used for multipoint subinterfaces.
The logic behind it is basically in point-to-point network the next-hop is always known and whatever the interface thrown at will be passed to the next-hop. All we need to do is to define what the interface DLCI number is.
For multipoint subinterfaces, the situation is different. One subinterface faces multiple end-points. Therefore, there is a need to define which DLCI mapped to which IP Address.