North American Network Operators Group
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Re: commonly blocked ISP ports

  • From: Luke Parrish
  • Date: Wed Sep 14 16:50:42 2005

Not quite looking for tips to manage my network and ACL's or if should or should not be blocking, more looking for actual ports that other ISP's are blocking and why.

For example:

port 5 worm 2.5
port 67 virus 8.2



At 03:12 PM 9/14/2005, [email protected] wrote:
On Wed, 14 Sep 2005 14:42:56 CDT, Luke Parrish said:
> We have a list, some reactive and some proactive, however we need to remove
> ports that are no longer a threat and add new ones as they are published.

All ports that are open are threats, at least potentially. What you *should*
be doing is:

a) When you block a new port due to a current exploit, log the fact.
b) Work with customers/users to make sure they're patched, and that new machines
are patched before they go live.
c) When probing for the port stops (which it never does), or some sufficient
number of downstream boxes are patched and safe, remove the block.

Either that, or block the world, and open ports on request.

Remember - *you* are the only one on this list who really knows if a given
port is a threat anymore....

(And that's totally skipping all the noise about corporate firewalls versus ISP
firewalls and different expectations regarding security/transparency...)
Luke Parrish
Centurytel Internet Operations
318-330-6661