RE: Unreachability detection at tunnels servers WAS: RE: Comments on zeroconf draft

["Christian Huitema" <huitema@windows.microsoft.com>]

> Now a standard last hop IPv6 router on a lan monitors the reachability
of
> its lan hosts using NUD and notifies of black holes by sending IPv6
> destination unreachable
> back to origin. (Actually the ICMP is generated when a NUD cache times
out
> and address resolution cannot be performed anew, but in this context 
> that's a detail.)

I don't think that in this age of firewalls, any application should rely
on ICMP packets for detecting that a destination is not reachable. Most
firewalls are programmed to silently drop the traffic they don't like...

That being said, Teredo hosts and relays can in fact use the Teredo
bubble mechanism to verify that their peers are reachable.

-- Christian Huitema