Question ref ".T" option in destination-pattern of dial peer

Unanswered Question
Jun 7th, 2007

I think I have a conflict of sorts between two of my ref sources in trying to understand ".T" behavior in matching destination patterns in dial peers and was wondering if someone could clarify...

I have one book telling me that "The T can be used to match a variable length string. ".T" matches any dial string that is not matched by another dial peer."

However another reference on Cisco's site says this...

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A default route could also be defined by using a single wildcard character with the timeout T-indicator in the destination pattern, as shown in the following example:

dial-peer voice 1000 voip

destination-pattern .T

session-target ipv4:10.10.1.2

You should be careful, however, when using the T-indicator for default routes. Remember, when matching dial peers for outbound call legs, the router places the call as soon as it finds the first matching dial peer. The router could match on this dial peer immediately even if there were another dial peer with a more explicit match and a more desirable route.

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What I'm wondering about is the warning at the end. How can that warning be true if (by definition) the ".T" pattern only matches anything that is not matched by any other defined dial peer?? TIA

I have this problem too.
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Paolo Bevilacqua Thu, 06/07/2007 - 15:55

Hi,

your wondering is justified. In fact, I believe the statement in the second reference is wrong.

See for example this other documents that makes an explicit example of a DP with an higher numbering and longer match, winning over a lower numbered one with T.

http://cisco.com/en/US/tech/tk652/tk90/technologies_tech_note09186a008010fed1.shtml

What is the URL for the second reference? It is always possible to have the documentation people to correct or remove the document.

Paolo Bevilacqua Thu, 06/07/2007 - 16:45

Hi,

I've been reading this better and I think that as in many cases with the cisco documentation, the paragraph need to be interpreted.

What it is really saying (I think), is like: "be careful with the timeout indicator, because if a timeout happens during digit selection, and there are DPs with more specific destination-pattern, these will be ignored". Thing that is, of course, correct.

Like if you have:

dial-peer voice 100 pots

destination-pattern 8204

port x/x

dial-peer voice 200 pots

destination-pattern 8T

port x/y

If an inter-digit timout occurs between 8 and 2, DP 200 will be selected. Else, matching will continue toward DP 100.

I hope my explanation makes some sense :)

flash2200 Thu, 06/07/2007 - 16:53

I guess I read it differently but yes I suppose it could possibly be interpreted that way. Thanks for the feedback on it!

Steven Holl Tue, 06/19/2007 - 13:51

Yes, all that document is saying is that you should always use a . or a digit proceeding a T. If you just have 'destination-p T' instead of 'destination-p .T', you risk really intermittent behavior with outbound dial-peer matching. Just a IOS quirk to look out for. You don't run the same risk with 'incoming called-number', though.

lagos Tue, 06/19/2007 - 17:06

I read the warning as this...

.T is not a suitable "last resort" dial-peer. Someone could dial 911, there could be a dial-peer match but it may chose the .T peer instead. In short, only use .T if it's the only peer you've got.

My .02,

CJ

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