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

  • From: Vinny Abello
  • Date: Wed Sep 03 15:18:33 2003 
At 02:51 PM 9/3/2003, Sean Donelan wrote:


On Wed, 3 Sep 2003, Johannes Ullrich wrote:
> I just summarized my thoughts on this topic here:
> http://www.sans.org/rr/special/isp_blocking.php
>
> Overall: I think there are some ports (135, 137, 139, 445),
> a consumer ISP should block as close to the customer as
> they can.

If ISPs had blocked port 119, Sobig could not have been distributed
via USENET.


Perhaps unbelievably to people on this mailing list, many people
legitimately use 135, 137, 139 and 445 over the open Internet
everyday. Which protocols do you think are used more on today's
Internet?  SSH or NETBIOS?

Some businesses have create an entire industry of outsourcing Exchange
service which need all their customers to be able to use those ports.

http://www.mailstreet.net/MS/urgent.asp

http://dmoz.org/Computers/Software/Groupware/Microsoft_Exchange/

If done properly, those ports are no more or less "dangerous" than
any other 16-bit port number used for TCP or UDP protocol headers.


But we need to be careful not to make the mistake that just because
we don't use those ports that the protocols aren't useful to other
people.
Even on Windows they can be used in a much safer fashion (although I would never attempt it for any of my stuff). It is possible to use IPSec policies on 2000 and higher to encrypt all traffic on specified ports to specified hosts/networks and block all other traffic. I bet some people are using this to join remote locations securely to each other for Windows networking with these ports and IPSec policies.

Vinny Abello
Network Engineer
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