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Re: Port blocking last resort in fight against virus
From: Jack Bates <jbates () brightok net>
Date: Tue, 12 Aug 2003 11:31:22 -0500

Mans Nilsson wrote:

Your chosen path is a down-turning spiral of kludgey dependencies,
where a host is secure only on some nets, and some nets can't cope
with the load of all administrative filters (some routers tend to
take port-specific filters into slow-path). That way lies madness.
Secure? Who's talking about secure? I'm talking about trash. Not blocking the port with a large group of infected users means that your network sends trash to other people's networks. Those networks may or may not have capacity to mean your network's trash.

Temporarily blocking 135 is not about security. A single infection within a local net will infect all vulnerable systems within that local net. A block upstream will not save local networks from cross infecting. However, it does stop your network from sending the trash out to other networks which may have smaller capacities than your network does.

Of course, perhaps a good neighbor doesn't really care about other people's networks? Perhaps there is no such thing as a good neighbor. It's kill or be killed, and if those other networks can't take my user's scanning them, then tough!

There is legitimate traffic on 135. All users I've talked to have been understanding in a short term block of that port. They used alternative methods. I have a lot of valid traffic still cranking out the other Microsoft ports.


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