what is a suitable scope for isc dhcp?

[Peter Grandi]

> could I get advice on how big dhcpd.conf file can be? the
> purpose is I want use dhcpd.conf to do authentication by
> using host xxx { hostware ethernet....}.

That's not such a good idea. That's not authentication, as it is
too easy to fake, and anyhow the proper way to do that is RADIUS.
However quite a few people think along your lines too.

> if I need list 30,000 host statement, is dhcpd will
> crash? or some perfermance isse? [ ... ]

If you check the archives for this mailing list there are a few
numbers, sometimes even larger.

> if possible isc dhcpd can work with database?

You seem to really want to use RADIUS.

> or if possible can seperate host statements from dhcpd.conf
> file as an extended file?

You can use an "include" statement.