[VoiceOps] Screwy DSL modem NAT troubles

[Alex Balashov]

On 02/21/2011 05:39 PM, Matthew S. Crocker wrote:

> Has anyone else noticed that the latest batch of DSL modems have
> broken NAT when it comes to VoIP?   I'm seeing stable VoIP customer
> get broken when the DSL modem is swapped out.  The modem NATs the
> phones to modem IP port 5060.  So, 10 phones behind the router
> become one phone to the SBC.  A race condition occurs and phones go
> in and out of service at random.  It looks like the router is
> trying to do a SIP ALG but very very broken.

Latest batch of which modems from which manufacturer?  :)

Trick that always works for me:

Change the phone signaling port to something else.  If that still 
doesn't work, change the phone's presentation of its external IP 
(Polycom phones, at least, have their own "let the phone help with 
far-end NAT traversal" settings) to something other than what the IP 
of the phone actually is.  It tends to confuse ALGs and make them turn 
off.

-- 
Alex Balashov - Principal
Evariste Systems LLC
260 Peachtree Street NW
Suite 2200
Atlanta, GA 30303
Tel: +1-678-954-0670
Fax: +1-404-961-1892
Web: http://www.evaristesys.com/