On Mon, 13 Oct 2008, Thomas Narten wrote:
1) We could ignore/deprecate the M&O bits and simply have any
client that implements DHCP invoke DHCP without even bothering to
see what the M&O flags say. I.e, the way DHCPv4 works today.
IMO, this approach would work fine. Indeed, it has the advantage
that the client won't do the wrong thing due to misconfigured
routers sending out M&O bits with the wrong setting. The main
downside is that operators would have no way of signalling to
clients that DHCP isn't available and they shouldn't waste
resources trying to invoke it. In the past, there has been
endless(?) debate about how significant the "waste" would be.
I don't see why M/O bits would need to be completely deprecated (they
could still be hints about what should be available in the network).
I've yet to see a DHCPv6 client implementation that would listen to
the flags in RA and conditionally start or stop the service depending
of the presence of flags there. It's more complex to implement and to
operate reliably. But granted I haven't done an extensive survey; I'd
be interested in knowing how existing implementations operate.
So I believe we're kidding ourselves if we think the DHCPv6 client
software writers and operating system SW engineers trying to figure
out a most reliable way to use DHCPv6 wouldn't start DHCPv6 client
automatically under every scenario, no matter the flags. These
implementations are not going to change no matter what we write in the
RFCs.
I don't believe the concern about wasting 802.11 airtime or other
bandwidth is severe enough in those peoples' (or my) mind that it
would justify the necessary complexity. There's a lot of other junk
that hosts spew out anyway (e.g. some won't like similar Bonjour
multicasts). If this is truly a problem, we could try to figure out
solutions for that, e.g. by tweaking the retransmissions or giving
operational guidance for filtering in switches / access points.
--
Pekka Savola "You each name yourselves king, yet the
Netcore Oy kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
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