At work, we use CVS for our version control. Then suddenly, it started taking a long time to authenticate into CVS. Before, it would be almost instantaneous, then it was taking more than 30 seconds. At first I thought it was perhaps something was slowing down the server where the repository was. But, after doing a "top", nothing was really going on with that server. Then a co-worker discovered that our computers were upgraded that included turning on the firewall. So, after opening up ports 2401 and 113, authentication speed was back to normal.
In Windows XP, this can be set by going to Control Panel/Network Connctions/Local Area Connection/Change settings of this connection. Then on the Advanced tab/Settings, add two services that allows these TCP ports to go through.