[ale] Kernel-2.4.0 oddness

[Chris Ricker]

On Thu, 11 Jan 2001, Thompson Freeman wrote:

> Possibly a truly dumb RTFM question, but what is ECN, why does ECN trip up
> the routers as often configured, and how should/can I check to make sure
> that I don't contribute to the misconfiguration?

ECN is explicit congestion notification.

If you want technical details, I think Sally Floyd's series of pages
<http://www.aciri.org/floyd/ecn.html> or else RFC 2481 would be the best
place to start, but basically, a flag can be set in the packet header to
indicate congestion, rather than relying on dropped packets as an
after-the-fact indicator of congestion.

Using ECN is a good thing.  The problem is that a lot of Cisco equipment on
the market has a bug in its stack which results in all packets in which the
ECN field is set being dropped on the floor....  Cisco has patches out to
fix that, but it'll be years / never before people at places like Ziff-Davis
actually bother to do their jobs and apply them....

For now, either disable it or be prepared to echo 0 in /proc a lot.  The
last estimate I saw (not sure how it was calculated, but anyway) was that 8%
of the 'net is inaccessible with ECN enabled.

later,
chris

-- 
Chris Ricker                                               kaboom at gatech.edu
                                              chris.ricker at genetics.utah.edu

--
To unsubscribe: mail majordomo at ale.org with "unsubscribe ale" in message body.