[OpenSIPS-Users] Source port in SIP replies

[Alexandr A. Alexandrov]

Hi!

I ran into a pretty weird situation last day. I'm using opensips-1.6.2 
as a load balancer for several * servers.
Everything worked fine for months, but suddenly opensips started to use 
ports like 56827 or 51234 (does not matter, just non-default, not the 
one it is listening on). And the operator's system does not allow such 
replies, it just drops them.
Opensips is listening on port 5070 on my system.

Invite comes like:
User Datagram Protocol, Src Port: sip (5060), Dst Port: vtsas (5070)
INVITE sip:xxxxx at my.ip:5070;user=phone SIP/2.0

Reply goes like:
User Datagram Protocol, Src Port: 52795 (52795), Dst Port: sip (5060)
SIP/2.0 100 Giving a try

Normally src port is always 5070.

So, the questions are:
- under what conditions does opensips decide to invent a new port?
- can I control this?

Thanks in advance,
Alex