We have 2 office connected with VPN., and in Ist Office I have a SIP phone.,

I want to register the sip phone to a internet SIP provider from the Ist Office., but SIP is blocked by the internet provider. From the 2nd office it is possible to register to the SIP provider.

Let us assume is the Ist office network and is the IInd office network,both are connected through IPSEC VPN (Router to Router)and I can access any hosts in both network.

Is it possible to write a iptable rule so that the SIP registration should go through the IInd office's gateway..,

Now I am registered the sip provider from a IPPBX in the Ist office and registered my phone in IInd office to the Ist office's IPPBX.., and it is working fine..,

Is there any other work around for this..