[c-nsp] NAT - SIP Problem

[Paul Stewart]

Hi folks...

Have a customer who has two ATA devices behind a Cisco Soho91 and having a
problem - trying to figure out if this is an IOS issue, a platform issue or
a Session Border Controller issue....

With the "original" ATA in place, things worked fine.  With a second ATA
hooked up, first one still works - second one doesn't.  With only the second
ATA in place it doesn't work.  When I say it doesn't work, the SIP
registration will not occur.

XYZ#sh ip nat translations
Pro Inside global      Inside local       Outside local      Outside global
udp xx.xx.111.3:5060   192.168.0.3:5060   xx.xx.98.6:5060  xx.xx.98.6:5060
udp xx.xx.111.3:1029   192.168.0.6:5060   xx.xx.98.6:5060  xx.xx.98.6:5060


I'm working on the hunch that the SBC is getting confused with this newer
ATA on the return traffic as the session stays in the NAT translations table
forever.  The "old" ATA is 192.168.0.3 and new is 192.168.0.6 - notice the
.6 ATA can't use 5060 on the outside interface as it's already in use.

A similar problem came up at another site a while ago (against the same
SBC's) and we converted it over to firewalled public IP space and worked
fine - kind of points me back to the way NAT is behaving on these routers
but could be an issue between the NAT and the way the SBC sees the
traffic....

Cisco Internetwork Operating System Software
IOS (tm) SOHO91 Software (SOHO91-K9OY6-M), Version 12.2(8)YN, EARLY
DEPLOYMENT RELEASE SOFTWARE (fc1)

Any input appreciated...

Paul