[Asterisk-Users] Re: Media Path Optimization & NAT

[Rich Adamson]

> >>>>>>Now, I would very much like to remove the "canreinvite=no" from the 
> >>>>>>provider's definition on sip.conf, but doing so causes Asterisk to send 
> >>>>>>a re-invite to the provider pointing to a private IP. I thought that 
> >>>>>>correct localnet entries would solve this...
> >>>>>>
> >>>>>
> >>>>>By changing to canreinvite=yes, are you expecting the asterisk box to
> >>>>>act as a router, passing rtp traffic from your sip provider through
> >>>>>the box to a sip phone with a private address (without passing
> >>>>>asterisk code in the middle of the rtp session)?
> >>>>
> >>>>No, sorry. I'm looking for Asterisk to not issue the re-invites if the 
> >>>>two devices can't see each other. Think of mobile users who are often 
> >>>>behind the corporate firewall but also travel. I'm trying to avoid 
> >>>>having the media path be "user->corporate lan->pstn provider". I want it 
> >>>>to be "user->pstn provider".
> >>>>
> >>>>If not to accomplish this, what are the localnet configuration entries for?
> >>
> >>>When a user is in the office, his phone registers with asterisk, and he
> >>>places calls through asterisk to the sip provider. But, when he's
> >>>out of the office, he takes his phone with him, and you are wanting
> >>>him to make use of the canreinvite=yes to allow his phone to connect
> >>>directly to the sip provider avoiding asterisk (from an rtp perspective). 
> >>>Is that right?
> >>
> >>Yes. A softphone on a laptop makes for a more believable example though.
> >>
> >>So, is this possible? And, if not, what do the "localnet" entries provide?
> > 
> > I don't believe what you want is possible. The issue is in how sip
> > handles reinvites and nating (or lack thereof). What will further
> > complicate this is the laptop, when out of the office, is likely to
> > be behind yet a different nat box and the addressing used behind
> > that box may be completely different from your office nat.
> 
> In that case, what are the localnet configuration parameters for?

Used for defining the asterisk environment when asterisk itself is
behind a nat box. See hints in sip.conf.sample:
 ; The externip and localnet is used
 ; when registering and communicating with other proxies
 ; that we're registered with
 ; You may add multiple local networks.  A reasonable set of defaults
 ; are:
 ;externhost=foo.dyndns.net      ; Alternatively you can specify an
  ; external host, and Asterisk will
  ; perform DNS queries periodically.  Not
  ; recommended for production
  ; environments!  Use externip instead

 ;externip =  ; Address that we're going to put in outbound SIP messages
             ; if we're behind a NAT