Passing H323 traffic via cisco 1605R

I am trying to pass H323 traffic through cisco 1605R. The traffic is initiated but somehow some acknowledgement don't pass through and the traffic is interupted.
In fact the H323 traffic is flowing from my pabx in my internal network via cisco to internet to another pabx.
The cisco router here is my internet gateway and also the NAT.
I have tried the same thing with simple Speedtouch and Sagem ADSL modem and they work fine.
I have this problem only with cisco - or may be my configuration???
I've tried the same with Cisco 835. Got same problem,
I have double check the NAT configuration and I know it is working.
Using ethereal, I can see the traffic being initiated with packets to and from my pabx from the remote pabx. But somehow an acknowledgement is sent but not received, then the whole communication is dropped.
Could be related with a specific port.
I have been struggling with that for weeks.
Help please.
Who is Participating?
grbladesConnect With a Mentor Commented:
So the device at your end is behind the cisco router which is performing NAT.
What is the situation at the other end?
Is the pbx on the internet or behind a NAT router?

It is probably NAT which is causing the problem. You need to fix the ports used and then forward these on the router. Some routers may recognise H323 traffic and automatically permit the replies coming back in to a different port.
brianvanschellebeckAuthor Commented:
Hi grblades,
Thanks for the response.
On the other end there is a speedtouch ADSL modem also performing NAT.
And when I replace the Cisco router with a similar modem, all works fine - VOIP traffic gets through
However I need to get it working on Cisco in order to benefit from features that are not available on speedtouch.
Here is my config:
interface Ethernet1
 ip address secondary
 ip address
 no ip unreachables
 no ip directed-broadcast
 no ip proxy-arp
 ip nat inside
 ip inspect standard in
 no cdp enable
interface Serial0.1 point-to-point
 ip address
 ip access-group 111 in
 no ip directed-broadcast
 ip nat outside
 no ip route-cache
 no cdp enable
 frame-relay interface-dlci 123  
## ROUTING/NAT section
ip nat inside source static
ip classless
ip route
Thanks to help.
As you wish to communicate directly between two devices on the local network at each site I would recomend that you use Cisco routers at each site and then configure a VPN between the sites and pass all the H323 over the VPN. That will avoid the use of NAT and make it far more reliable.
brianvanschellebeckAuthor Commented:
Problem was with Cisco NAT.
I have forwarded all traffic from cisco (without NATing) to a linksys broadband router and registered the internal address in the DMZ.
Now working.
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