Issues with SIP packets between VZ Fios and NTT

Brielle Bruns bruns at
Mon May 13 16:48:17 UTC 2019

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    /

More information about the NANOG mailing list