host-identifier with IPv6

David W. Hankins David_Hankins at
Tue Mar 3 02:14:40 UTC 2009

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 "";
    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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