[Serusers] NAT with multiple SERs

[Klaus Darilion]

Andreas Granig wrote:
> Juha Heinanen wrote:
> 
>> in summary: a load balancing solution that at the same time is redundant
>> is not possible using the participating sers alone.  some intelligent
>> front end help is needed and i'm not convinced yet that even that could
>> be done.
> 
> 
> What about this (maybe a special case):
> 
> I was just thinking about STUN, and AFAIK this relies on a NAT device 
> not matching the source IP of a datagram, so the client opens a NAT 
> binding to an STUN server to determine an external IP/port pair which is 
> filled in the Contact header. The Proxy then can also send SIP requests 
> to this external IP/port which is forwarded to the client by the NAT 
> device. Is this basically correct?
> 
> If so, it theoretically should work with transparent NAT handling on two 
> SERs too, if both SERs know the external IP/port of UAC-1.

That's fine. There is no problem with STUN-traverseable NATs. But there 
are problems with symmetric NAT and restricted NAT.

> I also think I know now why it didn't work for me: SER-1 got the request 
> from UAC-1 and stored the contact IP and the received IP in the location 
> table. SER-2 got the replicated register but stored SER-1's IP as 
> received IP:

True, ser-2 does not use fix_... for REGISTERs received from ser-1.

regards,
klaus