One of the most effective lab setups uses frame relay as its primary transport method. This is a configuration that many people use and praise for its ease of setup and maintenance. Topologies can be changed quickly and easily without touching a single cable. To accomplish this we configure a Cisco router as a dedicated Frame Relay switch that will act as a DCE device on the line. Frames from a Frame Relay PVC arriving on an incoming interface are switched to a Frame Relay PVC on the designated outgoing interface. The switching is performed completely in Layer 2, and the switch pays no attention to the Layer 3 information contained within the frames.
The path taken is completely based on the Frame Relay routing table we construct. Before we do this we need to think about ease of management. Choosing significant DLCI numbers can simplify this greatly, unfortunately the DLCI is limited to 1024, and only 16 – 991 are user definable. Using a method of concatenating Router X’s Number, the number 2 (to signify to the next router), and Router Y’s number. Using this method transport from router 4 to router 6 would use DLCI 426. This has the unfortunate side effect of limiting our lab to 9 routers.
Enough about theory, here is the configuration for a 3 router lab.
!
hostname FrameSwitch
!
frame-relay switching
!
interface Serial0/1
description Router_1
no ip address
encapsulation frame-relay
clockrate 64000
frame-relay intf-type dce
frame-relay route 122 interface Serial0/2 221
frame-relay route 123 interface Serial0/3 321
!
interface Serial0/2
description Router_2
no ip address
encapsulation frame-relay
clockrate 64000
frame-relay intf-type dce
frame-relay route 221 interface Serial0/1 122
frame-relay route 223 interface Serial0/1 322
!
interface Serial0/3
description Router_3
no ip address
encapsulation frame-relay
clockrate 64000
frame-relay intf-type dce
frame-relay route 321 interface Serial0/1 123
frame-relay route 322 interface Serial0/1 223
You can check your configuration using the show frame-relay route command. Here is a sample output based on our configuration above.
FrameSwitch#show frame-relay route
Input Intf Input Dlci Output Intf Output Dlci Status
Serial0/1 122 Serial0/2 221 inactive
Serial0/1 123 Serial0/3 321 inactive
Serial0/2 221 Serial0/1 122 inactive
Serial0/2 223 Serial0/1 322 inactive
Serial0/3 321 Serial0/1 123 inactive
Serial0/3 322 Serial0/1 223 inactive
I hope this helps your lab setup and studies. If you have any questions about this or anything, feel free to leave a comment. I’d love to help.
Who writes this crap?
Tony Mattke is a network engineer for a financial institution in Indiana. In the past he has worked for ISPs, data centers, networking manufactures, and the occasional enterprise. For feedback, please leave a comment on the article in question. For everything else including fan mail or death threats, contact him via twitter.
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Great Post! You write some great stuff. Keep it up!