wake on lan / wol with linux in IPv6-LAN (without IPv4)

Phil Mayers p.mayers at imperial.ac.uk
Mon Sep 22 11:51:37 CEST 2014

On 22/09/14 08:42, Ignatios Souvatzis wrote:

> But I imagine people might want to wake every host once a night
> and run some backup or software update remotely; so unconcerned
> machines would see, say, one or two packets times the number of
> sleeping machines per night. How many hosts do you have per broadcast
> domain? more than 2**8?

We have some IPv4 /21 with >2**10 hosts actually. They're managed 
machines and it's largely to work around the IPv6 address space wastage. 
It's marginally suboptimal from a "size of failure domain" PoV, but 
we've never actually had the sort of problems this can lead to in 
theory, and the alternative was worse.

Obviously single /64 IPv6 (bliss!)

> There's another consideration: if you do have the need, due to huge
> broadcast domains, nobody prevents you to make your machines
> subscribe to a locally assigned multicast address and send your

Erm... while they're asleep? Doubtful that would work - most network 
stacks end up dropping then re-initialising the ethernet link when they 
go to sleep, so MLD snooping state is likely to be cleared, and absent 
something like AMT/vPro (which comes with it's own IPv6 hassles ;o) to 
join the group in the sleeping link-state...

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