Problems with voice: messenger and ICS



I have an ADSL connection and two PCs running XP Professional SP2. One
PC is configured as an ICS host, and the other one is a client. I
cannot make a voice conversation from the client PC to the ICS host
using Windows Messenger 5.1.0639. The other way it works.

I have done some packet sniffing with ethereal, and below is a
simplified diagram of the messenger traffic between the clients (steps
1 - 3 are connected via a messenger server, which is not shown here)

1. A -> B INVITE
2. B -> A ACCEPT
3. A -> B ACCEPT IP-Address IP1:pORT1
4. B -> IP1:pORT1 SIP/SD Request: INVITE IP1:pORT1
contact IP2:pORT2
5. A -> IP2:pORT2 SIP Status: 100 Trying

Case 1:

Voice conversation is initiated from the ICS host,
i.e. A = ICS host, B = client

IP1 =
IP2 =

Both clients are using private addresses and the voice conversation is

Case 2:

Voice conversation is initiated from the ICS client,
i.e. A = client, B = ICS host

IP1 = 180.xx.xx.xx:58087

So, in the 3rd step in the diagram above, the messenger client finds
that it is behind a NAT device (ICS). By using upnp it finds the public
address (180.xx.xx.xx) and configures the ICS host to forward to the
client PC any incoming traffic on a dynamically allocated port 58087.

Next, in the 4th step, the ICS host tries to send its SIP request
directly to its peer using the address 180.xx.xx.xx:58087. The ICS host
has an entry in its routing table that delivers the request directly to
the address, i.e. localhost. Hence the request bypasses any
redirection rules for incoming packets and wont be routed to the client

Are there any known issues for this kind of setup running windows
messenger locally on the ICS host?

Or is there a bug in XP's NAT traversal API?

Ari Jasberg




Well, i didn't really read the technical stuff but my first question is:
what kind of firewall u got?

If it's Norton Internet Security then i can easily tell you whats wrong and
how to fix it (i had the same problem except with the games and activities


Please reply to this email so I know if i'm right :)

Good in Home Networking, XP Home based problems, and Pro based Problems
Add my email to MSN Messenger if u wish
(e-mail address removed) (remove spamfree)




I am not running any firewall on the private interfaces between the PCs, and
XP's firewall on the public (ADSL) interface.

"Jayso" kirjoitti:

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