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New Member

Frame-Relay "show interface" output

I have a router with a T1 frame-relay connection that im troubleshooting a VPN issue on. I dont think its a problem with the VPN box or the connection from the VPN box to the router, the VPN box diags and outputs are perfect and the connection is good, the config is good too. I'm suspecting the problem might lie in a dirty T1 line to the CO, there are a LOT of "input errors" on s0 interface of this particular router. I've noticed something else too that I wanted to get some input on because I really havent ever noticed this before. When I do a "show interface s0" command to show int stats for the s0 interface that corresponds to the T1 CSU/DSU I notice the following two lines in addition to all the input errors:


MTU 1500 bytes, BW 1536 Kbit, DLY 20000 usec,


Available Bandwidth 1152 kilobits/sec


Shouldn't the two bandwidth indicators match? Is the available bandwidth a measurement taken real-time telling you whats left on the line minus the traffic thats going through it, or is that actually the true available b/w from my router to the CO?

Thanks in advance.

VIP Purple

Re: Frame-Relay "show interface" output


regarding the difference between the available bandwidth shown and the T1 speed:

By default the router keeps 25% for rotuing protocols, line maintenance, RSVP, and all the other queueing techniques.

You can change this with the max-reserved bandwidth (#) command.

So if you wanted to keep just 10% for e.g. the routing protocols, you would do max-reserved-bandwidth 90.

The input errors could have various reasons, e.g. a noisy line from your provider, a bad CSU/DSU, or a bad cable. Check out this link for detailed troubleshooting info on input errors (you need a CCO login to view this document):




Re: Frame-Relay "show interface" output

The Available Bandwidth line refers to the number of timeslots configured on the CSU/DSU service module. In your case, it looks like 18 channels of the T1 are enabled (1152/64 = 18). Check your interface configuration. It has the command "service-module t1 timeslots 18". Do not change this number unless you are sure that a different number of timeslots are enabled by your carrier.

The BW number is manually configured and does not affect the operation of the router, except in the case of calculating EIGRP and OSPF metrics. It will also affect the way that network management systems will report on bandwidth utilization. And yes, the two numbers should match for the sake of accurate reporting, but their not matching would not account for the problems you are seeing.

It is most likely a case of the dirty T1 line. Having several input errors is not proof by itself, though. The errors could be historical if the counters have not been cleared. You must see whether or not the number of errors is incrementing rapidly to see if the line is currently bad. In fact, the "show service-module serial" command will be a better indication of errors received on the T1 in each 15 minute interval over the last 24 hours. Here is a link to that command:



New Member

Re: Frame-Relay "show interface" output

Thanks for the help guys. I have all 24 timeslots enabled though, thats what I wasn't understanding.

Georg was right on, I changed the max-reserved-bandwidth to 90 and the available bandwidth went up to 1382 kb/s. Now my question is: how much should I keep reserved? I am not running ANY routing protocols on this router. The only thing going across this frame-relay link is data to my ISP. I have one static route in the routing table and thats it.

Thanks for showing me the "show service-module serial" command Mark, that should help me figure out what's going on here.