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New Member

calls from E1 are going back to E1 (AS5300) BUG??!!

Hello All

I have an AS5300 ,

I reciving calls from a pbx (teles ) and im sending the calls to ip ( voip) , but if i make a dial-peer pots with the same destination patern the call will go back to E1 and not to voip (and the voip dial peer is configured )

Is this a bug?? Or is posible to send calls from pots to pots?

here are some details :

version :Version 12.2(15)T5

flash:c5300-is-mz.122-15.T5.bin

Anyway i have fix the problem with a prefix in the front of the nr (in this case i dont have an dial peer pots and a dial peer voip with the same destination pattern )

what i whant to know : did somebody have this problem too? and what is the reason that this is happening?

Cheers

4 REPLIES
Silver

Re: calls from E1 are going back to E1 (AS5300) BUG??!!

IT's not a bug - POTS to POTS calls are called hairpinning. Without seeing you configs, I would be guessing you have wildcard destination pattern on you outwards POTS dial peer (.T or similar). Since the router thinks that this is a close enough or best match on the DNIS that came in from the POTS, it sends the call straight back out again.

The solution is to always make sure your destination patterns are very specific. We have seen smart people use this for toll fraud - they are able to figure out the call is being sent back out to the PSTN so they make a local call into the gateway and then the gateway reroutes the call out again to another number - this means the owner of the gateway router gets the bill for the second call!

New Member

Re: calls from E1 are going back to E1 (AS5300) BUG??!!

I have understood now....

this is a option that i didn`t know about ...

i have read on cisco docu page about this ...but i didnt fiind how to disable hairpinning

cheers

New Member

Re: calls from E1 are going back to E1 (AS5300) BUG??!!

It is possible to stop hairpinning, by using the "Hunstop" command in the voip dial-peer. But you have to check it is well matching first the voip dial-peer, you may be using "preference" for this purpose.

Henry8-)

Silver

Re: calls from E1 are going back to E1 (AS5300) BUG??!!

The only way to disable hairpinning is to not have any post dial peers the point back to the PSTN. If the gateway is only used for inwards (POTS to VOIP calls) then this is easy to set up -

!

dial-peer voice 1 pots

description - enable DID for inwards calls

incoming called-number .

direct-inward-dial

port 1/0:15

!

this dial peer will allow the inwards calls, but since it has no destination pattern, any calls that comes in from the POTS will not be able to be looped back out to the POTS again.

If you must have outwards POTS dial peers, then you need to be selective with the destination patterns on them. If the calls come in from the IP network, prepend the numbers with a unique access code, and have this as the destination pattern on the POTS dial peers. The POTS dial peer would strip this access code off , but it would ensure that any calls that come in from the PSTN will not be able to be hairpinned back out -

dial-peer voice 1 pots

description - allow inwards DID (POTS --> VOIP) calls

incoming called-number .

direct-inward-dial

port 1/0:15

!

dial-peer voice 2 pots

description - outwards calls (VOIP --> POTS) with leading access code of 5555

destination-pattern 5555

port 1/0:15

!

Any call that comes in with a leading 5555 (eg 555584460000) would match on dial peer 2. The leading 5555 would be stripped off, so the number sent out to the PSTN would be 84460000. It would be highly unlikely that a number would come in from the PSTN with a called number starting with 5555 so there would be little chance of the call being hairpinned.

The best way to prevent call hairpinning is to use very specific desztination patterns on the dial peers !

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