host-identifier with IPv6

[David W. Hankins]

On Tue, Mar 03, 2009 at 02:07:51PM +1300, Eustace, Glen wrote:
> > Looking at this problem from another angle, how would you feel about
> > assigning an IPv6 address to any client seen on a given switch port?
> 
> Ahhh, no thank you.

Ah, pity.  When Shane wrote the IPv6 host bits, we talked and decided
on the host-identifier syntax explicitly for this kind of reason.  I
was hoping there'd be a hardware address option eventually (or
environments where you could pull it from relay forward options), and
I knew there would be situations you'd want to use the hostname, or
relay agent supplied options, like those that describe the switch port
the client's packet was received on.  I wanted to backport it to
DHCPv4 as well, since we get feature requests there all the time.
It's remarkably trivial to backport.

So I gave him the impossible task of a config option that the user
specifies the matching constraint, while still being a hash-table
lookup and not some series of byte-compiled conditional stages.  The
host-id syntax is how he solved it.

    host-identifier option fqdn.fqdn "foosrv.example.com";
    host-identifier option agent.circuit-id "eth0";

Doesn't help for registration (since even if there was a hardware
address option, clients today don't send it; you still need an
interim solution).

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins
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