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Re: What do you want your ISP to block today?

  • From: Iljitsch van Beijnum
  • Date: Sat Aug 30 14:28:02 2003

On zaterdag, aug 30, 2003, at 18:54 Europe/Amsterdam, Owen DeLong wrote:

Christopher L. Morrow's mention of asymmetric routing for multihomed
customers is more to the point, but if we can solve this for all those
single homed dial, cable and ADSL end-users and not for multihomed
networks, I'll be very happy.

I happen to look alot like a single homed ADSL end
user at certain levels, but, I'm multihomed.  I'd be very annoyed if
my ISP started blocking things just because my traffic pattern didn't
look like what they expect from a single homed customer.
I'm sure knife salespeople find it extremely annoying that they can't bring their wares along as carry-on when they fly. Sometimes a few people have to be inconvenienced for the greater good.

But, TCP to a port that isn't listening (or several ports that aren't
listening) _ARE_ what you are talking about blocking.  This is not a
good idea.
Why not? I think it's a very good idea. TCP doesn't work if you only use it in one direction, so blocking this doesn't break anything legitimate, but it does stop a whole lot of abuse. (Obviously I'm talking about the case where the lack of return traffic can be determined with a modicum of reliability.)

It should be possible to have a host generate special "return traffic"
that makes sure that stuff that would otherwise be blocked is allowed
through.

I don't think it's desirable or appropriate to have everyone re-engineer
their hosts to allow monitoring and external validation scans to get
around your scheme for turning off services ISPs should be providing.
But then you don't seem to have any problems with letting through denial of service attacks so I'm not sure if there is any use in even discussing this with you. Today, about half of all mail is spam, and it's only getting worse. If we do nothing, tomorrow half of all network traffic could be worms, scans and DOS. We can't go on sitting on our hands.





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