You’re using using a NAT based sharing program (ICS, Sygate, etc.) or hardware router and are having trouble getting ICQ to work.

(Thanks for Collin Witwer for his help!)

You’ll need to open a number of ports in the firewall that comes as part of your sharing software or hardware router.

attentionsml-1574860If you are going to open holes in your firewall, please read this information on Security.

The exact method you use to open ports varies with the program or router that you are using.

For other programs or hardware routers, consult your Help files.

Here’s what you need to do:

1) Map UDP port 4000 in ICS to allow your client computer to communicate with the ICQ server. Do this both outbound and inbound.

Info on firewall configuration for ICQ is at:

Ignore the information about Socks4 and Socks5 proxies, since NAT routers don’t provide these.

2) Configure ICQ on your client to work behind a firewall.


This may be all you have to do, but if you have problems communicating directly with other users (client to client) vs. through the ICQ servers, you’ll need to take the next steps:

3) Open a range of TCP “listening ports” in ICQ

4) Open the same range of TCP ports in ICS.
(Example: If you open the ICQ recommended range of TCP ports 2000-4000, then open this same TCP port range in ICS.)


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