Protocol Summary

Yahoo is an instant messenger software from Yahoo.

Communication

Yahoo! can connect by several ports(Maybe the most complicated). Yahoo! use tcp port 5050 as the main connection port. If 5050 is unreachable, it will try ports 21,23,25,20,27,37,119,80 and others until it finds a workable one. Yahoo! also can connect via a http/sock4/sock5 proxy server.

How to block Yahoo?

Because Yahoo can switch port automatically, so you can not block them only by disable the ports in the firewall. We recommend you to block Yahoo in two ways:

• 1). Block all Yahoo server IP address.Find Yahoo server IP address and block all the server IP address.
• 2). Use firewall which has deep content inspection capabilities.Use firewall which has deep content inspection capabilities to block Yahoo's P2P function.

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