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ip phones and nat

Does nat work for ip phones in the following situation that I have:

ip phone has a public address, ccm has a nonpublic address.

Router is the 4224 gateway, using ios 12.1(5)YD.

I cannot nat a direct, static, public-ip-to-private-ip. (But I can nat single static ip-to-ip tcp or udp ports). There is only one external ip address. The internal LAN, with private ips, is using nat with overloading.

The TFTP server is on the ccm.

*****

I have tried the command suggested in the document at:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121t/121t5/dtnipcm.htm

I believe the ccm is using port 2000, according to the debug packet details results on the 4224.

The issue I have come against is that the phone cannot get it's load from the tftp server (the internal ccm). It makes a request to udp port 69 on the router. I natted that port to the ccm. However, to continue the tftp session after acknowledging the tftp server on port 69 the phone makes requests to the tftp server using a pool of ports in the 3000-4000 range. It's not practical to enter nat commands for all those ports.

This is as far as I have gone. Is there a way nat a range of external ports to an internal ip address, given these conditions? Or am I off track?

1 REPLY
New Member

Re: ip phones and nat

I heard the PIX firewall dynamically opens the high ports based on the h.323 negotiation. I suspect this functionality would be required if you don’t want to open all the ports. Maybe a proxy server http://www.cisco.com/univercd/cc/td/doc/product/voice/sipproxy/admingd/ver1_0/overview.htm would be a better option for you.

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