>I think this is the appropriate change.  Historically, as we've improved
>our TCP, we have gradually turned on the new features by default after some 
>time has passed to demonstrate that they actually work as expected.  Path
>MTU was off because we didn't have blackhole detection and thus knew there
>were problems.  Since you added blackhole detection, I don't think there's
>any reason for Path MTU to be off by default (Jason?  Kevin?).

	hmm.  maybe the kernel change is the way to go.  anyways,
	i think it nice to have more information in sysctl.conf,
	i may work on it when i have time.

itojun