Same experience here, with Comcast, at least 15 years ago. What was striking was that the tunnel had to be encrypted; plain old GRE tunneling worked for everything else, but GRE-encapsulated VoIP packets never arrived at the other end of the tunnel. We ended up just backhauling all traffic from (and to) that office over an encrypted tunnel to our nearby datacenter. Go figure. This was Comcast business service, with a publicly routed (i.e., not RFC 1918) /27 allocated to it.

Jim Shankland

We've just moved to tunneling anything VoIP if on Comcast's network.

-----
Mike Hammett
Intelligent Computing Solutions

Midwest Internet Exchange

The Brothers WISP

---

From: "Matt Hoppes" <mattlists@rivervalleyinternet.net>
To: nanog@nanog.org
Sent: Tuesday, September 10, 2024 2:17:37 PM
Subject: Third Party VoIP Over Xfinity

I have an employee who has recently switched to Xfinity cable service.
Ever since they switched their internet service their work phones will
not stay registered for more than about 3 minutes.

These same phones have been used on many ISPs without issues.  The same
config has been used behind multiple levels of NAT without issues.

She was fine, until she switched to XFinity.

Of course, XFinity support is absolutely worthless.

Anyone from XFinity Tier 3 or such that might be able to offer assistance?

I suspect it's something stupid with either NAT overload in the modem or
the modem not keeping the SIP channels open.

I've tried playing around with registration times without any success.
And again, we've never had issues with these phones or this setup with
any other ISP.