Viewing Frame Relay Status Information

Problem

You want to check the status of a Frame Relay circuit or VC.

Solution

There are several useful show commands for looking at Frame Relay circuits and virtual circuits. It is usually best to start at the physical layer and work upward through the protocol layers. You can look at the physical interface with the show interfaces command:

Central#show interfaces Serial0 

The show frame-relay pvc command allows you to see information about each of your Frame Relay PVCs:

Central#show frame-relay pvc

And sometimes it is also useful to look at the LMI status:

Central#show frame-relay lmi

 

Discussion

The show interfaces command has a lot of useful information. When the interface is configured for Frame Relay, this command shows the LMI configuration, whether the interface is configured for SVCs as well as PVCs, and it also shows you whether the interface is set up to be DCE or DTE. But the most important thing to look at is always the first line, where it shows the physical and the protocol status:

Central#show interfaces Serial0 
Serial0 is up, line protocol is up 
 Hardware is HD64570
 Description: Frame Relay connection
 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
 reliability 255/255, txload 3/255, rxload 3/255
 Encapsulation FRAME-RELAY, loopback not set, keepalive set (10 sec) 
 LMI enq sent 263, LMI stat recvd 263, LMI upd recvd 0, DTE LMI up
 LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0
 LMI DLCI 0 LMI type is CCITT frame relay DTE
 FR SVC enabled, LAPF state down 
 Broadcast queue 0/64, broadcasts sent/dropped 44/0, interface broadcasts 0
 Last input 00:00:03, output 00:00:03, output hang never
 Last clearing of "show interface" counters never
 Input queue: 0/75/0 (size/max/drops); Total output drops: 0
 Queueing strategy: weighted fair
 Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
 Conversations 0/2/256 (active/max active/max total)
 Reserved Conversations 0/0 (allocated/max allocated)
 5 minute input rate 24000 bits/sec, 0 packets/sec
 5 minute output rate 23000 bits/sec, 0 packets/sec
 2838 packets input, 1604468 bytes, 0 no buffer
 Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
 2951 packets output, 1623730 bytes, 0 underruns
 0 output errors, 0 collisions, 20 interface resets
 0 output buffer failures, 0 output buffers swapped out
 2 carrier transitions
 DCD=up DSR=up DTR=up RTS=up CTS=up
Central#

If the interface is up, you should be able to see useful PVC information:

Central#show frame-relay pvc

PVC Statistics for interface Serial1 (Frame Relay DTE)

DLCI = 100, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.1

 input pkts 1271 output pkts 1312 in bytes 843519
 out bytes 856138 dropped pkts 0 in FECN pkts 0
 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0
 in DE pkts 0 out DE pkts 0
 out bcast pkts 40 out bcast bytes 11320
 pvc create time 01:08:11, last time pvc status changed 00:39:42
Central#

This output tells you, for example, that the PVC with DLCI 100 is active and configured on interface Serial0.1. None of the packets received on this interface have had their FECN, BECN, or DE bits set. This is the most useful place to check for congestion in the Frame Relay cloud. Note that the router is unlikely to ever set the FECN or BECN bits when sending packets, so the inbound counters are the most useful here.

The last line of this output for each PVC is particularly useful if you have a problem with flapping PVCs in the carrier cloud. In this case, you can see that the PVC has been active for just over an hour, but it had a status change 39 minutes ago. This doesn't tell you what caused the status change, though. In a stable network, you should not expect to see frequent PVC status changes. So this gives you a useful indication of problems either in the carrier cloud, or with your remote router.

Note that the show frame-relay pvc command will list all of the PVCs on a router, including any that are configured on the router but not in use, as well as any that are configured on the switch but not on the router. If you want to focus on a particular PVC, you can specify the one you want by its DLCI number:

Central#show frame-relay pvc 100

If you suspect an LMI problem, it is useful to look at the output of the show frame-relay lmi command:

Central#show frame-relay lmi

LMI Statistics for interface Serial1 (Frame Relay DTE) LMI TYPE = CCITT
 Invalid Unnumbered info 0 Invalid Prot Disc 0
 Invalid dummy Call Ref 0 Invalid Msg Type 0
 Invalid Status Message 0 Invalid Lock Shift 0
 Invalid Information ID 0 Invalid Report IE Len 0
 Invalid Report Request 0 Invalid Keep IE Len 0
 Num Status Enq. Sent 299 Num Status msgs Rcvd 299
 Num Update Status Rcvd 0 Num Status Timeouts 0
Central#

The first line of this output shows that the LMI type in this case is CCITT, which is configured with the frame-relay lmi-type q933a command. The other options are cisco and ansi, both of which use the same type field in the output of this command as in the configuration command.

Because LMI is the Frame Relay management protocol between the router and the switch, if you have an LMI problem, the usual symptom is that the physical interface is up, but the protocol is down and none of the PVCs will come up. If you repeatedly check the show frame-relay lmi command, you will see the Num Status Timeouts field incrementing. Because it can take several seconds for an interface to come up, it is sometimes hard to tell immediately if you have the right LMI type field, so this field gives you a relatively quick indication of when you have the right configuration.





Cisco IOS Cookbook
Cisco IOS Cookbook (Cookbooks (OReilly))
ISBN: 0596527225
EAN: 2147483647
Year: 2004
Pages: 505
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