In message <200601261959.OAA00374@Sparkle.Rodents.Montreal.QC.CA>,
der Mouse writes:

>>> The real problem is on the other end: hosts which try to do PMTU-D,
>>> but are behind boxes (usually misconfigured firewalls) which drop
>>> the ICMPs necessary for PMTU-D to function.
>> Not only, some PPPoE setup just won't send the ICMP unreachable
>> message, because the equipement at which the MTU is lowered doesn't
>> appear at the IP level.
>
>You mean things like ATM?  But that won't listen to the DF bit, either,
>will it?  So there's no issue (except the loss rate increase provoked
>by fragmentation).
>
>Or you mean there are setups which silently drop too-large packets
>without any notification to anyone?  

Yes, I htink that's precisely what is meant.  Welcome to the
PPoE-over-(DSLAM+ATM) world.

I have trouble calling those
>anything better than grossly broken, 

See previously-snipped text from earlier in the thread; the problem is
"not under our control", nor under our users' control.  Some of us
(like you and I) are lucky enough to live in regions where retail
domestic-consumer ISPs don't force us to put up with this.  Others are
not so lucky, and have no practical recourse except to work around the
misfeature.

Again, welcome to the real world.