Odd firewall problem.

[Daniel Roethlisberger]

Cameron <hiryu@21andover.com> wrote:
> I can view webpages on some servers, but not others from systems
> behind the firewall, but I CAN view these webpages from these
> servers from the firewall itself (using lynx).
[...]
> I'm using Pacific Bell ADSL via PPPoE, and have been the whole
> time, even before this problem came about.
[...]
> http://people.unix-fu.org/andreasson/index.html
> idsoftware.com

Broken path MTU discovery. Usually caused by braindead sysadmins
who block all ICMP, not letting through vital types of ICMP
messages. Those two sites seem to block all ICMP.

Solutions: first, get the sysadmin(s) in question to let through
ICMP Destination Unreachable; second, set your clients MTU to
1452; and third clamp the TCP MSS down to 1412. rp-pppoe does this
for you, you just need to enable it in /etc/ppp/pppoe.conf; or
else you can use netfilter to clamp it down.

See http://www.worldgate.ca/~marcs/mtu/ for some more information
on the problem.

Cheers,
Dan


-- 
   Daniel Roethlisberger <daniel@roe.ch>
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