Re: ECN: Clearing the air (fwd)

Miquel van Smoorenburg
2001-01-28T14:34:13Z

In article <Pine.SOL.4.21.0101281324210.26837-100000@yellow.csi.cam.ac.uk>,
James Sutherland <jas88@cam.ac.uk> wrote:
>On Sun, 28 Jan 2001, jamal wrote:
>> The internet is a form of organized chaos, sometimes you gotta make
>> these type of decisions to get things done. Imagine the joy _most_
>> people would get flogging all firewall admins who block all ICMP.
>
>Blocking out ICMP doesn't bother me particularly. I know they should be
>selective, but it doesn't break anything essential.

It breaks Path MTU Discovery. If you have a link somewhere in your
network (not at an endpoint, or TCP MSS will take care of it) that
has an MTU < 1500, you cannot reach hotmail and a lot of other sites
either currently. It _does_ break essential things. Daily. I would
get a lot of joy from flogging all firewall admins who block all ICMP.

Mike.