Possible solution for -8 and other connection errors

Question

I've been struggling recently to make connections with people, often seeing the -8 error. This happened even with the most simple network setup we could find, with our routers either running with uPnP enabled or disabled, and ports forwarded or not. Often we could connect individually to the Apple test accounts, but not each other.
The fix that worked for me, and also for someone else on these boards, was to look at our network "ports" on the Macs themselves. Not the TCP/UDP ports, but the "ethernet" , "airport", etc.
If you open system preferences, Network, and from the Show: dropdown at the top choose "Network Port Configuration" you will see the hardware network ports on your machine. If you use your machine in multiple environments, such as with a wired Ethernet port, Airport, perhaps a Firewire network too, your Mac may have several IP addresses assigned to itself, even if only one is active. Installing virtualization software such as Parallels adds more ports here, with more IP numbers.
Whilst running iChat in debug mode, and watching outbound connections through Little Snitch, I saw that firstly iChat thought I had multiple IP addresses which it attempted to open uPnP with, and secondly my outbound packets had the private internal IP address of one of the Parallels network ports the person I was trying to communicate with - which would never be delivered.
What we did was disable all the ports in the System Preferences described above, except for the one in use. We then restarted iChat and our video streams opened! I believe that iChat simply gets confused about which IP address to do its uPnP mojo with, and disabling the ones not in use makes it choose the correct one.
If you follow this advice, remember to re-enable the ports you disable when you use want to use them in future.
I'm convinced this is the cause of the problem - even when I use my MacBook behind a commercial locked down Watchguard firewall the video conferencing still works, which suggests that it's not the opening of ports through the firewall that's the issue, at least for some people.
I hope this is useful information for people struggling with -8 errors - let me know how you get on.

Answer 1

Intel macs, since 25 febr.
"watching outbound connections through Little
Snitch"
Interrupted connections under some circumstances
after applying the AirPort Extreme 2007-001 update:
This is (often) soluble by disabling any third-party
wireless signal monitoring or sniffing utilities.
I don't think Little Snitch was causing any problems, for me at least. It did let me see that it was trying to talk to the other machine's non-active IP address, which is what led me to turning off the other network ports.
It's quite informative to see which TCP and UDP ports are being actively used, and where they're going.