VoIP SBC Problems

Unanswered Question


I am trying to configure SBC on a 7200 router to allow non-sip complient router/fw's on the outside to use our VoIP infrastructure - in this case a connection to our AS5300 and out to the PSTN.

I have the following configuration that allows me to connect but I don't get any sound.

Does anyone have a working SBC configuration I can take a look at?



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paolo bevilacqua Fri, 06/29/2007 - 11:38
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Do they use use SIP ? Do you use NAT ? Which IOS do you have on the 7200 ?


Yep, SIP is the protocol. The flow of things is as follows:

1. Client uses SIP softphone to connect to our global IP

2. That hits my 7206(12.4(11)T2 IOS) and gets NAT'd via SBC -- this is the part that isn't really working!

3. Then hits my PIX515E FW and that global address is translated to an internal address and then hits the router.

I have the following config in place:

ip nat sip-sbc

proxy 5060 5060 protocol udp

session-timeout immediate

mode allow-flow-around

override address

ip nat translation timeout 10

ip nat translation tcp-timeout 10

ip nat translation udp-timeout 10

ip nat pool call-id-pool netmask

ip nat inside destination list 111 pool call-id-pool

As I say, the call connects but I just don't get any sound....


paolo bevilacqua Fri, 06/29/2007 - 16:27
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Hi Antonony,

I'm not familiar on the sip-sbc configuration and don't know the specifics on that. What I can tell you, I have a SIP phone working ok through regualt NAT (inside to outside) with same IOS as yours - no configuration required.

The other day also tried a PIX with a static NAT configuration (1 to 1 mapping), again, no problem.

Sorry I can't tell what the problem is, perhaps you could try to take one of the two NAT out of the equation and see if that helps.


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