[Serusers] STUN and Symmetric NAT

[Simon Barber]

My confusion over symmetric / cone NAT. But does look possible to 
communicate between symmetric NATs in many cases - but first starting 
with RTP proxy or TURN. Using the RTP proxy to learn which class of 
symmetric NAT you have, and predicting the port allocation - then 
switching to direct communication if the port prediction test gives good 
results.

Simon


Jiri Kuthan wrote:

>At 07:16 PM 3/15/2004, Simon Barber wrote:
>  
>
>>possible way to get through symmetric NAT without permanent rtpproxy.
>>
>>Initiate the connection using rtpproxy, as normal. Now, learn the udp port the NAT is sending RTP from. Now send a re-invite to both parties, and switch the stream to the udp port the NAT is using, instead of the rtpproxy. This will only work if the NAT uses the same external ip/port pair when the same internal ip/port pair is used
>>    
>>
>
>Which is non-symmetric NAT. Symmetric NATs are only traversable the way
>Klaus described. 
>
>-jiri
>
>  
>
>>(and I'm expecting that most sip phone will reuse the same internal ip/port pair when you re-invite). Apparently some NATs do this. (although I'm not a NAT expert - I have only read a few papers on the subject).
>>
>>Simon
>>
>>
>>Klaus Darilion wrote:
>>
>>    
>>
>>>You can't overcome symmetric NAT with STUN. To traverse a symmetric NAT you need:
>>>- A SIP proxy with NAT traversal (nathelper module)
>>>- An RTP proxy (or an generic TURN server and a SIP UA which supports TURN)
>>>- A symmetric SIP UA (symmetric SIP & symmetric RTP)
>>>
>>>regards,
>>>Klaus
>>>
>>>      
>>>
>>>>Hi,
>>>>Can someone please help me if my dialer does not support symmetric
>>>>signalling,  is there anyway to go through symmetric nat through the server
>>>>or configure from the server that asking the dialer to point to a STUN
>>>>server before reaching the UA. Please help........
>>>>regards, shirley
>>>>
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>>>>        
>>>>
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>>>
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>>    
>>
>
>--
>Jiri Kuthan            http://iptel.org/~jiri/ 
>
>  
>