[Serusers] Trouble with Record-Route

[Frank Durda IV]

I have a situation where SER sits between two independent
networks, one being an isolated network and the other being
the rest of the Internet.   The isolated network is also
a PSTN gateway with only one switch on that network.
SER has two physical interfaces, and uses force_send_socket
and rewritehost to make sure things go out the right interfaces.

The problem is when the called network hangs up first and
generates a BYE* first, if SER didn't add a record-route,
the called network switch bypasses SER and attempts to send
directly to the calling IP address, which doesn't work because
the two networks cannot be reached directly.

If I add just one record-route in SER, the called
network now knows how to get back to SER to tell it about
the BYE, and SER passes that BYE on to the calling network.
So far so good.

Unfortunately, this also causes the called network to add
Record-Route to responses it sends out, like 183/200 with its
own IP address.  Those reach the SER without problem, but SER
doesn't add its own Record-Route to the reply, so when this
reaches the calling network, they only have a Record-route
that points to an IP address they cannot possibly reach.

I tried a number of things to get around this, and
all failed.
1.  Tried to add my own Record-Route to the reply, but
SER doesn't allow this.  Won't even start.

2.  Tried to remove the Record-Route from the reply, but
SER also doesn't allow this.  Won't even start.

3.  Tried to add both IP addresses for the two interfaces
to by using two Record-Routes at the INVITE.  This doesn't
fix the response messages, and actually causes looping
behavior or "I'm terribly sorry" responses.  (I tried this
with and without the "enable_double_rr" parameter set
and it didn't seem to make any difference.)   By altering
the order of the two Record-Route you are pretty-much
guaranteed to confuse one party or the other as each
needs the Record-Routes listed in the opposite order.

4.  Tried some combinations of the above with loose_route()
but the usual outcome is SER sending messages back to itself
rather than to the right place and eventually the dreaded
"I'm terribly sorry" or "481 Transaction" gets sent out,
usually to nobody in particular.


So, are there any working examples out there for a SER
that has two network interfaces, each in its own isolated
network that correctly route messages between the two sides?
I need SER to not only add Record-Routes when appropriate
but to strip them off or replace them as the replies pass
back through and back to the initiator.


The network isolation was a security thing, not a NAT thing
(although private IP space is in use), but it is not possible
for a message from one network to reach the other without
passing through SER, and some commercial equipment I am
working with ignores the source of a message and only
sends the response to wherever the record-route(s) say it
should go and if no record-route, it honors the Via, while
other gear ignored both and only replies to the source of
the message.

*The problems affecting called-party BYEs also causes
major grief when re-INVITEs occur, which fail to make it to
the calling network (or more likely, the 200 OK replies
fail to make it back), causing the call to die after 32
seconds.


Any examples would be greatly appreciated.