CCNA Cisco Certified Network Associate Study Guide - FTP Server

Here’s an example using the Frame Relay map command:
Frame Relay 499
RouterA(config)#int s0
RouterA(config-if)#encap frame
RouterA(config-if)#int s0.16 point-to-point
RouterA(config-if)#no inverse-arp
RouterA(config-if)#ip address 172.16.30.1 255.255.255.0
RouterA(config-if)#frame-relay map ip 172.16.30.17 16 ietf
broadcast
RouterA(config-if)#frame-relay map ip 172.16.30.18 17
broadcast
RouterA(config-if)#frame-relay map ip 172.16.30.19 18
Here’s what we did: First, we chose configured interface serial 0 to use the
encapsulation type of Cisco (default), then we created our subinterface. We
then turned off inverse arp and mapped three virtual circuits and their corresponding
DLCI numbers.
Notice that we changed the encapsulation type for the first mapping. The
frame map command is the only way to configure multiple frame encapsulation
types on an interface.
The broadcast keyword at the end of the map command tells the router
to forward broadcasts for this interface to this specific virtual circuit.
Remember that Frame Relay is a nonbroadcast multiaccess (NBMA) encapsulation
method, which will not broadcast routing protocols. You can either
use the map command with the broadcast keyword or the neighbor command
within the routing process.
Instead of putting in map commands for each virtual circuit, you can use
the inverse-arp function to perform dynamic mapping of the IP address
to the DLCI number. This makes our configuration look like this:
RouterA(config)#int s0.16 point-to-point
RouterA(config-if)#encap frame-relay ietf
RouterA(config-if)#ip address 172.16.30.1 255.255.255.0
Yes, this configuration is a whole lot easier to do, but it’s not as stable as
using the map command. Why? Sometimes, when using the inverse-arp
function, configuration errors occur because virtual circuits can be insidiously
and dynamically mapped to unknown devices.