Configuring a frame relay switch (or frame relay cloud)

Ever since I have started out cisco networking career last year I have only learned how to configure routers to connect the frame relay cloud, nothing and not a single thing was mentioned on how to configure the cloud or what’s inside the cloud, the cloud was mystified as if it was some kind of top-secret project that no one ever wanted to mention in their books.

Thanks to Mr. Chris Bryant, he has a configuration on how to set up a frame relay switch for use in lab.

Here’s the link http://www.thebryantadvantage.com/Frame%20Relay%20Switch.htm

To configure a frame relay switch properly, I need to draw out the intended diagram.

Image may be NSFW.
Clik here to view.

Based on the diagram, the router connected to Se0/0 of FRS is the convergence point for other site routers, frame relay route would need to be implemented on Se0/0 so that FRS will know which interface to exit when the frame relay packet arrives.

To configure frame relay routing use the command:

frame-relay route <dlci entrance 16 – 1007> interface serial <x/x> <dlci exit 16-1007>

Configure serial 0/0 of FRS:

FRS(config)#int se0/0

FRS(config-if)#no ip address

IP address is not necessary in the switch, to the routers the frame relay cloud does not exist, it only see the next router beyond the cloud.

FRS(config-if)#encapsulation frame-relay ietf

Configure the encapsulation using open standard.

FRS(config-if)#no frame-relay inverse-arp

Inverse ARP is not needed here, it is needed for routers connecting to the cloud to indentify which dlci to exit in order to reach the other end. For example Site Router 1 needs to route to Converged Router, inverse ARP tells the router in order to reach the ip address of the converged router it needs to exit from dlci 102.

FRS(config-if)#frame-relay intf-type dce

Synchronous serial needs clocking for bits to be sent over the serial medium. DCE is usually a modem, in this case the FRS act as the clocking device and hence DCE.

FRS(config-if)#frame-relay route 102 interface serial 0/1 201

FRS(config-if)#frame-relay route 103 interface serial 0/2 301

Configure the frame-relay route for the site routers. There are two site routers. frame-relay route <source dlci from 16-1007> interface <destination serial interface> <destination DLCI from 16-1007>

FRS(config-if)#logging event dlci-status-change

FRS(config-if)#logging event subif-link-status

Configure the syslog messages for events involving DLCI status and sub interfaces link states.

FRS(config-if)#clock rate 512000

FRS(config-if)#exit

Configure the clock rate and exit the interface.

Configuration of the other serial interfaces that are connecting to the site routers.

FRS(config)#int se0/1

FRS(config-if)#encapsulation frame-relay ietf

FRS(config-if)#clock rate 512000

FRS(config-if)#no frame-relay inverse-arp

FRS(config-if)#frame-relay route 201 interface serial 0/0 102

FRS(config-if)#logging event subif-link-status

FRS(config-if)#logging event dlci-status-change

FRS(config-if)#no ip address

FRS(config-if)#frame-relay intf-type dce

FRS(config)#int se0/2

FRS(config-if)#no ip address

FRS(config-if)#encapsulation frame-relay ietf

FRS(config-if)#frame-relay intf-type dce

FRS(config-if)#clock rate 512000

FRS(config-if)#logging event dlci-status-change

FRS(config-if)#logging event subif-link-status

FRS(config-if)#frame-relay route 301 interface se0/0 103

FRS(config-if)#no frame-relay inverse-arp

To verify frame relay routing use this command:

FRS#sh frame-relay route

Input Intf      Input Dlci      Output Intf     Output Dlci     Status

Serial0/0       102             Serial0/1       201             inactive

Serial0/0       103             Serial0/2       301             inactive

Serial0/1       201             Serial0/0       102             inactive

Serial0/2       301             Serial0/0       103             inactive

Tip: Frame relay DLCI concept is best understood by using the airport analogy explained by Mr. Jeremy Cioara.