Issues with SIP packets between VZ Fios and NTT

Dovid Bender dovid at
Mon May 13 16:20:10 UTC 2019

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.

On Mon, May 13, 2019 at 11:40 AM Brielle Bruns <bruns at> wrote:

> On 5/13/2019 9:21 AM, Dovid Bender wrote:
> > Hi,
> >
> > Over the last 48 hours we have been getting a lot of alerts of customers
> > phones losing registrations to us. All the complaints are coming from
> > customers that are on VZ Fios in the NYC area. Anyone else see anything
> > strange going on?
> >
> While you are diagnosing, might check to make sure that the SIP ALG is
> disabled on all of their routers too.
> --
> Brielle Bruns
> The Summit Open Source Development Group
>    /
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