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Walkthrough Wednesdays

dial-peer and debug issue explanation

A new lab setup

2821 router with 2 E1 ports and a back-to-back E1 connected between them - on the same router

Both ports Up & Multiple_Frames_Established.

Well the Call is Ringing & getting connected - I just do not understand how and why is the debug dialpeer and debug isdn coming out so wierd.

IpPh1 - DN 1501

IpPh2 - DN 07531883443

A Route pattern 9.xxxxxxxxxxx in CUCM poiting to the H323 GW.

Call from IPPh1 1501 to IpPh2 07531883443. I want the call to go via the route pattern, hit the H323 GW and match the dial-peer:

dial-peer voice 1 pots

destination-pattern 0T

port 0/2/0:15

forward-digits 11

and then come put the other side E1 port, match incoming called-number . dial peer and then:

dial-peer voice 2 voip

destination-pattern T

session target ipv4:

I did not put a 0T here as I wanted the call to get a better match with dial-peer 1 pots and go out the E1 port - which it is doing - alleast I think so.


I see this single call getting connected 3 times - I see 3 setups, I see Interface Serial0/2/0:0 is now connected to 07531883443 AND Interface Serial0/1/0:1 is now connected to 1501 3 times

I know I have 3 channels configured - but why is every channel getting connected?

What wrong am I doing please?

Assist. sh run and debugs attached.


I feel that there is a loop , this a pb of B chanelles

the idea is to have a

  • incoming VOIP dial peer (for calls from call manager to your gateway)
  • outgoing pots (from gateway to PSTN  )  PST for you is your gateway
  • incoming pots (from PSTN to gateway )PST for you is your gateway
  • outgoing voip (from gateway to callmanager)

so try the following dial peer

dial-peer voice 1 voip

incoming called-number .

dial-peer voice 2 pots

destination-pattern 0T

port 0/2/0:15

forward-digits 11

dial-peer voice 3 pots

incoming called-number .


dial-peer voice 4 voip

destination-pattern T

session target ipv4:

if this did  not correct it can you make establishing the call and during the active call

sh call active voice brief


Hi linuxchild

It did not help ... but I found this:

I had 3 dial peers already - you asked to me add 'dial-peer voice 1 voip; incoming called-number .' as well - but I thought this was being taken care by the default dial peer already.

I think - but you correct me if I am wrong - The reason I was getting this loop was because destination-pattern 0T was getting matched going when I dialed 07whatever originally - then this 07 number coming out on the other side E1 port was also matching this same dial-peer and taking the second channel and then again the third channel.

So sh call active v brief was showing 6 active call legs.

I changed destination-pattern 0T to destination-pattern T so that both dial peer are equally matched - this resolved it - I see 2 active call legs in sh call active v brief and debugs are coming out all right now as well.

BUT I am still confused that when I dial 07whatever - since both dial peers are exact & equal match being destination-pattern T - why does the router picks up the pots dial peer first and when this call comes out on the other side E1 on the same router - how and why does it match the voip dial-peer to give the call to the call manager.

How is the router intelligent enough to do this on its own - any ideas please?

Thanks & Regards,

Kartik Bhatia


I will answer your first question

It is not recommanded to match the dial-peer Zero , (the default dial-peer) , not good practice

for the second question give me some time , I will try to simulate it is my lab tonight or this weekend and let you know



Hi Kartik,

Whenever two or more dial-peers have equal preference(in your case preference 0), the gateway will use the dial-peers in round-robin fashion starting with the one which was created first. Hence in your case, when the outbound dial-peer has to be matched to route call out the pots line, the gateway matches the dial-peer 2 pots(since this was created first). Similarly when the call comes in from the pots line and has to be sent to the CUCM, the router uses dialpeer 4 voip since it has to use the dial-peers in round-robin order. Next time when you make a call, it again uses pots first and then voip.




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