Issues with SIP packets between VZ Fios and NTT

Dovid Bender dovid at
Mon May 13 17:04:45 UTC 2019

Good ol UDP encrypted.

On Mon, May 13, 2019 at 12:49 PM Brielle Bruns <bruns at> wrote:

> On 5/13/2019 10:20 AM, Dovid Bender wrote:
> > Thought of that. Customers have their own CPE's. So far the only thing
> > mutual here is that it's NTT -> VZ. Here is what I found so far looking
> > at two Polycom phones using non standard ports (e.g. not 5060)
> > 1) PhoneA tries to register multiple extensions and for each request we
> > send a 401. We expect to get back a REGISTER request with a no-once but
> > we don't. This happens for a while and then magically it starts working.
> > 2) PhoneB tries to register the time time as PhoneA and has no issues.
> >
> > At first I thought it was something possibly with the SIP call-ID but I
> > ruled that out since in the same SIP DIALOG it was not working then it
> > started. Also the seems to be per phone each phone is behind NAT and the
> > traffic is coming from a different NAT'd port. Seems like there is some
> > device in the middle that is randomly dropping traffic on specific
> sessions.
> Are you using TLS encrypted SIP or just plain ol' cleartext?
> If its encrypted, I'd look at possibly there being a MTU/MSS issue
> somewhere along the path possibly?
> --
> Brielle Bruns
> The Summit Open Source Development Group
>    /
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