Testing NAT types (was: Re: [Serusers] Re: RESOLVED - nathelper / calling UAs behind symmetric NATs)

[Jan Janak]

That's too complex and I couldn't see what is this good for. There is no
way of notifying the registrar. Registrar can only receive REGISTER
requests, process them and send a reply.

If I understand it correctly you try to mimic STUN with SIP, but that
will result in unwanted overhead.

If you want to eliminate the RTP proxy when two UAs are behind the same
NAT then you could use Via and Request-URI of the INVITE message to find
out whether they are behind the same NAT.

  Jan.

On 05-01 18:03, Thilo Salmon wrote:
> On Mon, 2003-12-29 at 20:41, Andres wrote:
> [Detecting UAC behind symmetric NAT based on Header fields]
> > ATA186(fw 3.0.0) and Sipura SPA2000 both have STUN Support.  I have asked for 
> > this "Header" feature to Sipura and they are thinking about it.
> 
> Thinking about a general solution the following came to my mind: How
> about setting up a 2nd UAS listening at a 2nd IP address and configure
> the registrar to forward REGISTER messages from UACs found to be behind
> a NAT to this 2nd UAS. This other UAS could then test whether or not it
> can "ping" the UAC. Unless this 2nd server would receive a reply from
> the UAC, we could assume that the UAC is behind a symmetric NAT. On
> success this second UAS would then notify the registrar to not force
> UAC's rtp stream through a local proxy.
> 
> Such as
> 
>    UAS A       -------->     UAS B
>                <-------            
>    /\ \           6.          / /\ 
>      \ \                     / /   
>       \ \                   / /    
>        \ \  2.         4.  / /     
>         \ \               / /      
>      1.  \ \             / /       
>           \ \           / /  5.    
>            \ \         / /         
>             \ \       / /          
>              \ \     / /           
>               \ \/ \/ /            
>                                    
> 
>                 UAC
> 
> with UAS A being the "real" registrar and UAS B being the UAS testing
> for the type of NAT.
> 
> 1. REGISTER
> 2. 200 OK
> 3. same message as 1.)
> 4. OPTIONS
> 5. 200 OK or 486 BUSY
> 6. ???
> 
> However, setting this up I ran into two issues. 
> 
> I configured UAS B to issue an OPTIONS message by calling 
> exec_msg("serctl ping"). I have no idea to do this stateful and did not
> find any mandatory header fields in the reply ("contact" appears not to
> be mandatory according to RFC 3261), which would reveal the identity of
> the UAC.
> 
> Also, I wonder what message one could use for the 6th message. '200 OK'
> as a reply to the 3rd message seems to make the most sense, but I
> noticed that one cannot use usrloc's save command inside
> onreply_route[]. Is there a message type that can be used for this sort
> of notification?
> 
> Thilo
> 
> 
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