• 08/01/2013
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Debugging Cisco Voice: How To Streamline The Process

Going through pages of debug output from a Cisco Voice Gateway is tedious and time-consuming, but there's a filtering tool that can make the job easier. Here's how to use it.
I recently discovered the “call filter match-list” command, and I only wish I had realized this tool was available during my years as a voice consultant. Perhaps I just missed it, but I cannot recall coming across it in my voice studies. I haven't seen it used in the wild even though it’s been available on Cisco IOS Voice Gateways since release 12.3(4)T. I may be late to the party, but let me fill you in on how this command can change your voice world.

See, the call filter match-list command works much like an access list applied to a typical network debug. Instead of plowing through pages and pages of debug output from a busy voice gateway, you can use this command to trim down the information to just to the phone calls you are looking for.

The configuration is quite simple. First, you create the call filter match-list in global configuration mode. The syntax to get started looks like this:

call filter match-list 1 voice

From this point, you can define one or several criteria to match, including, but not limited to, incoming calling number, outgoing calling number, incoming port, outgoing port and dial peer.

Below is what a filter designed to match on outgoing calling number and outgoing voice port would look like:

call filter match-list 1 voice outgoing calling-number 5555555555 outgoing port 0/1/0

The next step is to enable the filter with the “debug condition match-list 1 {exact-match | partial-match}” command. I personally prefer to start with exact match, and then switch over to partial match if I don’t see the debug output I am expecting.

Once the filter is enabled, you then turn on the debug you want from the debugs that work with the call filter list. This feature supports many of the more common debugs you would use, including debug isdn q931, debug voip ccapi inout, debug ccsip messages, debug vtsp. The full list can be found in the documentation for the command on the Cisco website.

[For help in diagnosing external calls failures on Cisco Unified Communications Manager, read "Troubleshooting External VoIP Calls on Cisco UCM."]

Once enabled, all of these normally chatty debugs will be filtered down to the criteria you set up in the call filter list. For example, if the filter above were used as exact match, then only calls with the outgoing calling number 555-555-5555 and matching the outgoing defined voice port would be part of the debug output.

If you have configured your call filter list and are wondering if you applied it correctly, you can always do a show debug and you should see something like this:

#show debug The following ISDN debugs are enabled on all DSLs: debug isdn error is ON. debug isdn q931 is ON. (filter is ON)

Notice the (filter is ON). Also, if you had partial match as the criteria for your debug call filter list, you would see “debug condition match-list is set to PARTIAL_MATCH” when you entered this command.

To turn off the filter, just enter the “no debug condition match-list 1” and you will see that filter is OFF and no longer enabled on your voice debugs.

Call filter list is a great way to save time when going through your voice debugs, especially when you don’t have a low call volume window to work with. I am certainly glad to have this little command addition to my problem-solving tool bucket.

Special thanks to @CollabJonathan who recently tweeted about the call filter match-listcommand.

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