[Serusers] NAT with multiple SERs

[Juha Heinanen]

Klaus Darilion writes:

 > 2. If the client sends the response back to ser-2, the port on the NAT 
 > may be different than the port for communicating with ser-1. Thus, the 
 > replicated location (port) stored in ser-2 will be different to the NAT 
 > binding for ser-2.

yes, i figured this out too yesterday.  

even if we would do what jan suggested, i.e., use 301 to make sip ua
send another register request to ser-2, location table entry for this
sip ua would be different in ser-1 and ser-2, because nat would not use
the same port for ser-1 and ser-2.

this means that if one ser goes down and comes back up again, it cannot
get its location memory populated from the other ser's location db.  if
it uses its own location db, chances are high that it is not up to data
anymore and thus not all sip uas are anymore reachable via this ser.

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.

-- juha