The Bryant Advantage Bulldog Blog

Chris Bryant's Facebook Fan Page

Join Me On Twitter For CCNA and CCNP Updates!

Over 500,000 Views On Our Video Training Channel!

Subscribe To My RSS Feed!

Network With Me On Linkedin!

 

 

 
 
 
 
 


CCNA Certification Training:

Frame Relay Switch Configuration

A Cisco Lab Case Study - Now Includes Two Video Tutorials!

By Chris Bryant, CCIE #12933

A Cisco lab's frame relay switch is not a switch at all; it's a Cisco router. Almost any Cisco router can serve as your frame switch, but you will need multiple serial interfaces to make a router particularly effective in this role.

I recommend you get a Cisco router with at least four serial interfaces. Cisco 2520s make excellent frame switches, and by doing a search on eBay for "frame relay switch", you'll quickly find several others that can as well.

The frame relay switch is going to play the role of the frame provider in your lab. In essence, you've got a one-switch frame relay cloud, which gives you a tremendous opportunity to practice frame relay scenarios.

In this example, I've got three Cisco routers that are going to be the production routers in my lab - R1, R2, and R3. I have a fourth router that will serve as the frame relay switch. The DLCI assignments I've come up with are as follows:

  • R1 is the hub and will use DLCI 122 to reach R2, DLCI 123 to reach R3.
  • R2 is a spoke router and will use DLCI 221 to reach both R1 and R3.
  • R3 is a spoke router and will use DLCI 321 to reach both R1 and R2.

The physical connections are as follows. All connections are using DTE/DCE cables with the DCE end of the cable connected to the frame relay switch.

  • R1 is connected to the frame switch's Serial1 port.
  • R2 is connected to the frame switch's Serial2 port.
  • R3 is connected to the frame switch's Serial3 port.

On the frame switch, the global command frame-relay switching is required to make the router act as a frame relay switch. Let's take a look at the commands we'll need on the frame switch's Serial1 port, which is connected to R1.

interface Serial1
 no ip address
 encapsulation frame-relay
 logging event subif-link-status
 logging event dlci-status-change
 clockrate 56000
 no frame-relay inverse-arp
 frame-relay intf-type dce
 frame-relay route 122 interface Serial2 221
 frame-relay route 123 interface Serial3 321

Note that there is no IP address on the port, and frame relay encapsulation is enabled. The clockrate command is necessary on the DCE end of the connection, so you see it here.

You also see that the interface is hard-coded as a DCE with the frame-relay intf-type dce command. Not all current IOS versions require this; just make sure you have the DCE end of the cable attached to the frame switch and verify that with show controller serial x.

Finally, we come to the frame-relay route command. The syntax seems a little tricky, but once you break it down it's pretty simple.

  • frame-relay route 122 = the incoming DLCI
  • interface serial2 = data coming in on DLCI 122 is sent out this port
  • 221 = data sent out interface serial2 will use this DLCI

Getting those statements correct is the hardest part of configuring your frame relay switch. The good part is that once you have your frame switch configured and working properly, you can just leave the configuration there.

We'll take a look at how to verify your frame switch configuration in just a moment, but first, let's review the important section of the frame switch configuration we've talked about here.

hostname FRAME_SWITCH
!
!
ip subnet-zero
no ip domain-lookup
frame-relay switching
!
!
!
interface Ethernet0
 no ip address
 no ip directed-broadcast
 shutdown
!
interface Serial0
 no ip address

interface Serial1
 no ip address
 no ip directed-broadcast
 encapsulation frame-relay
 logging event subif-link-status
 logging event dlci-status-change
 clockrate 56000
 no frame-relay inverse-arp
 frame-relay intf-type dce
 frame-relay route 122 interface Serial2 221
 frame-relay route 123 interface Serial3 321

!
interface Serial2
 no ip address
 no ip directed-broadcast
 encapsulation frame-relay
 logging event subif-link-status
 logging event dlci-status-change
 clockrate 56000
 no frame-relay inverse-arp
 frame-relay intf-type dce
 frame-relay route 221 interface Serial1 122

interface Serial3
 no ip address
 no ip directed-broadcast
 encapsulation frame-relay
 logging event subif-link-status
 logging event dlci-status-change
 clockrate 56000
 no frame-relay inverse-arp
 frame-relay intf-type dce
 frame-relay route 321 interface Serial1 123

To verify that your frame relay configuration is functioning correctly, run the global command show frame route on the frame relay switch. If you see active next to all frame routes as shown below, you're in good shape.

CCNA Certification Lab  Frame Relay Switch Config

If you see anything else - say, the word "inactive" - then there is a problem.

Troubleshooting A Frame Relay Switch

The key to troubleshooting your frame switch is that you cannot concentrate on the frame switch's config. You can get that part perfect, but if you're using other DLCIs on your routers or there's a physical issue - perhaps you forgot to open some interfaces - you're not going to get the active frame routes you want.

Just make sure you're got all the appropriate interfaces open, don't forget the clockrate and frame-relay route commands on the frame switch, and you'll successfully add this important component to your Cisco home lab!

Part 1:

 

And part 2! Enjoy!