[asterisk-users] Why Nat=yes Nat=no Option?

[Steve Totaro]

On Wed, Nov 12, 2008 at 4:47 PM, Alex Balashov <abalashov at evaristesys.com>wrote:

> Steve Totaro wrote:
>
> > I have done some large installs where people are going to be in the
> > office, sometimes out, work from home, it always changes sorta
> thing......
> >
> > I have found that setting all device profiles to Nat=yes "Just Works"
> > whether they are on the LAN or not and this is even on larger scale
> > systems with hundreds of "phones".
> >
> > Is there any reason why this would be frowned upon as a default?  Even
> > to the point of, if nat= is not specified, it would default to yes?
> >
> > Is there a performance hit somewhere, or some other downside?
> >
> > If not, I suggest making it the default.
>
> The premise of nat=yes is that the domain portion of the Contact URI is
> overridden with the real, received source IP of the request and that the
> default expectation of port 5060 (if not specified in the Contact URI)
> is dropped in favour of the actually received source UDP port.
> Similarly for SDP (without SIP-aware ALG).
>
> I think the reason this would be frowned upon as a default is
> philosophical in essence;  by default, per the RFC, a SIP UAC is
> expected to behave such and such way, i.e. use the Contact URI that
> arrives in a REGISTER request and/or INVITE.  Overriding that with the
> received IP:port is a "hack" around prescribed behaviour, and enabling
> hacks as default behaviour is generally considered a bad idea.
>
> --
> Alex Balashov
> Evariste Systems
> Web    : http://www.evaristesys.com/
> Tel    : (+1) (678) 954-0670
> Direct : (+1) (678) 954-0671
> Mobile : (+1) (706) 338-8599
>
>
While not taking the time to look, and if memory serves me correctly, LAN
devices appear on the correct ports even with nat=yes.  I may be wrong....
I will have to double check this when I have a moment.

So if a "hack" overwrites something with the same something then did you
really break the RFC?

-- 
Thanks,
Steve Totaro
+18887771888 (Toll Free)
+12409381212 (Cell)
+12024369784 (Skype)
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