Unanswered Question
Aug 24th, 2009
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I have IP PBX, NAT router (cisco) and SIP-phone connected as follows:

IP PBX<-internet->NAT router<-LAN->SIP phone

The problem: When I make a call from SIP phone to IP PBX the connecting goes correctly. But when I call from IP PBX to SIP phone the connection does not established. Help to fix it.

NAT router has following config:

interface FastEthernet0/0

ip address

ip nat inside

duplex auto

speed auto


interface FastEthernet0/1.89

encapsulation dot1Q 89

ip address

no ip proxy-arp

ip nat outside


ip nat pool ourpool netmask

ip nat inside source list 10 pool ourpool overload


access-list 10 permit

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craiglcve Tue, 08/25/2009 - 13:22
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What address would the IP PBX be sending the SIP invite to? The issue is that when you call from inside out a nat translation is created that pairs the source address with the destination address. When you call from the IP PBX to the internal phone there is not a translation for the destination. You would need a static translation for the phone so the Router knows who to send the call to.

In a nutshell I think thats whats happening. Hope that helps.


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