Need help badly w Cisco 79x1 phones - not registering

Good day all!

I am hoping someone in this forum can help or knows of someone that can.

I have a client with 60 phones…all of them Cisco 79x1s…I have uploaded the configs correctly, moved from SCCP to SIP firmware…everything is great…until it tries to register.

These phones are located in remote offices behind Linksys routers.

How do I get them to register? I can’t port forward as we have multiple phones in each location. Been playing with Nat settings, but really need a definitive answer on what both the freepbx and the phone configs should look like.

And yes, I have been to…fantastic site…just missing this one piece.

Thanks in advance!

Personally, I have never had to much luck with Cisco SIP and NAT. One thing to try is a softphone like x-lite at one of the remote offices to see if there is a possibility of joy.

Also, have you the ability to try one or more of the phones on the LAN ( same LAN as the PBX) and make sure they work at all?

The only way I have ever had this work is using router based VPN between locations.