asterisk users - Mar 2004 - Asterisk for different networks in different cities

Hi all,

I have installed Asterisk and SIP calls are successfull inside our office.
Then I created some extensions for my colleagues in other city. As our 
offices are connected trough a dedicated point-to-point line, by now 
I'll just create the extensions for the "remote" people in the
Asterisk
machine at my side of the line just for testing...

OK. Now problems arise...

    * city-A has an IP addressing in the form 172.20.1.x/255.255.224.0
    * city-B has an IP addressing in the form 192.168.0.x/255.255.255.0

In /etc/asterisk/sip.conf I see this parameter:

    localnet = 172.20.1.0

Is it possible to have something like: localnet = 172.20.1.0, 192.168.0.0 ?

The routes to reach city-B from the Asterisk host are OK, and the router 
on city-B has the right configuration to reach city-A.

Now, when a user in city-B registers into Asterisk, or I attempt to call 
somebody there I see this message on console:
---
*CLI> Mar 23 06:47:03 WARNING[229391]: chan_sip.c:495 retrans_pkt: 
Maximum retries exceeded on call 
D5628230-09C4-4839-902E-86DF85DCDA02@192.168.0.203 for seqno 1 (Response)
---

Of course, both firewalls allow traffic between both ends...

Some example users from boths offices (user1 in city-A, user2 in city-B):

[user1]
type=friend
username=user1
secret=foo
host=dynamic
dtmfmode=rfc2833
defaultip=172.20.2.x
restrictcid=no


[user2]
type=friend
username=user2
secret=foo
net=yes
host=dynamic
dtmfmode=rfc2833
defaultip=192.168.0.x
restrictcid=no


Any thoughts?

TIA.

Best regards,
Martin