[sr-dev] why new tcp connection?

Klaus Darilion klaus.mailinglists at pernau.at
Fri Nov 6 15:55:14 CET 2009

Klaus Darilion schrieb:
> Juha Heinanen schrieb:
>> Klaus Darilion writes:
>>  > 2. server
>>  > I use the pragmatic, and well working UDP approach. Just call  > 
>> fix_nated_contact/register also for TCP clients. I never had any 
>> issues  > with that.
>> even when client is not behind nat like in the example of the
>> discussion?
> In this case it can work also with client receiving responses/in-dialog 
> requests at advertised port (as long as the client is really listening 
> on the advertised port).
> But one of my favorites statement is: "Never trust the user". As the 
> contact and Via headers are user provided data I do not trust it. Thus I 
> always enforce symmetric signaling, regardless if client is behind NAT 
> or not and regardless of the used protocol.*

Of course this has some limitations too - e.g. if a local user uses a 
proxy between client and my proxy - I will incorrectly rewrite the 
contact to the socket of the other proxy. But in typical service 
provider deployments there should not be proxies inbetween, or the proxy 
should be able to recover from this.


> The only exception is if the client is known to be asymmetric (then I 
> have to screen the contact that at least the IP is the src_ip).
> regards
> Klaus
> * I once used the somehow "academic" approach with hyper-intelligent NAT 
> detection methods, but I ended up with the "pragmatic" approach which is 
> easier, more secure and works IMO better.
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