How to make a sip phone register properly behind a Checkpoint Firewall

When the SIP phone that resides behind the checkpoint firewall tries to register with the SIP Proxy on the internet, the checkpoint firewall will use the IP from the firewall as the registering IP for the phone. The registering IP needs to be the IP of the internal IP address of the phone or the SIP proxy will not know how to reach the phone to direct a call to it.
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No, If you use the Private IP address behind the Firewall as your registration IP, there is not routing capability.  

Your Firewall and you IPBX need to be SIP / NAT aware, and I don't know the settings for your Checkpoint.  

MorganGunterAuthor Commented:
Found a solution to the problem. By adding a local SIP Proxy that communicates with the main external proxy the phones will register with the internal proxy first that sits behinds the customer firewall. The Local DNS server will direct the sip registration to the internal proxy so the phones will properly get register with the main VOIP PBX.

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MorganGunterAuthor Commented:
Found my own solution as the firewall would not allowed the phones to register.
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