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Sams Teach Yourself Network Troubleshooting in 24 Hours, Second Edition by Jonathan Feldman

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Troubleshooting Port Access Using Proxies and Port Forwarding

If you’re having trouble using a certain port through your firewall, you might want to test whether this port is specifically being blocked—not necessarily at your site, but perhaps somewhere upstream from your site. Let’s say, for example, that you cannot use Gnutella—the popular file-sharing program doesn’t seem to be able to contact any of the “host discovery” services. Although Gnutella runs on many ports, the most popular “discovery” port is TCP/6346, and it’s a common port blocked by firewall administrators; that is, many folks make this an explicitly forbidden port to traverse the firewall.

What if your AUP (acceptable use policy) says “Don’t do file sharing”? Okay, leave ...

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