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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: ISPs are asked to block yet another port
[email protected] ("Christopher L. Morrow") writes: > ISP's could block all ports and save everyone the hassle of having an > Internet.... (I am just kidding of course) > > Two interesting points though: > > 1) Spammers adapt > 2) default insecure OS installs cause problems 3) thoughtless reactionism at isp's does little good and sometimes some harm. take for example port-25 blocking. i've been getting relayprobed all weekend by someone who gets around outbound at&t's tcp/25 SYN blocking by sending their SYN's through a provider who shall remain nameless (except that chris morrow happens to work there :-)) using at&t IP source addresses. i guess they multihomed their host and bind()'d the outbound socket to one interface even while making sure the routing used a different interface. high rocket science? NOT. so if you're going to block tcp/25 SYNs on outbound, please make sure you block SYN/ACK's on input too, or else you just give the spammers a little more work to do instead of a lot more work to do. -- Paul Vixie
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