[H-GEN] mtu = 576 on ppp0

[Gavin Unsworth]

> Also watch out for ECN which is characterised by an inability to send
> email to some remote sites for no apparent reason while all others work
> 100%.  Yay.

FWIW it's not just email but any packets - I was misinformed that ECN
problems were characterised by an inability to deliver email. Which is
partly true. I did more research on the ECN issue after having problems with
web access to certain sites (www.sony.com.au, www.lastampa.it for anyone
that wants to test).

More information on ecn here:

http://lis1.ph-freiburg.de/~peter/ecn.html

It's worthwhile double checking the default status of ECN when you roll a
new kernel. I've since added the appropriate line to my firewall script.
It's trivial so I wont bother sharing it. j/k here it is:

echo 0 > /proc/sys/net/ipv4/tcp_ecn

It's the sort of problem that doesn't immediately manifest itself so can be
particularly nasty/embarrassing.



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