Analysis and Solutions, you are not alone in your dhclient troubles.

I've been following your adventure for a few weeks now, as I scanned the
archives because of a problem I was having with my Netgear FA311 ethernet
card (NatSemi DP83815 chip) and dhclient, while trying to connect to my
cable internet service provider (Telstra Bigpond Advance, in Australia).

Specifically, dhclient would core-dump on me every time without fail (the
default version of dhclient which came with the 1.5 release ISO).
Following the advice which Chris Pinnock gave you, I downloaded the latest
source and compiled myself an (unofficial) 1.5.1 kernel of sorts with the
driver
fix for the NatSemi cards and also got myself the latest dhclient from the
ISC
website. Now dhclient would no longer core-dump, but a new problem arose,
which looks something like this (no doubt a familar sight for yourself):

    DHCPREQUEST on sip0 to 255.255.255.255 port 67
    ip length 352 disagrees with bytes received 354.
    accepting packet with data after udp payload.

As with your case, I played with the configs in /etc (dhclient.conf,
resolv.conf) and also the /var/db/dhclient.leases file, but to no avail.
No amount of rebooting, killing and restarting dhclient, or reinstalling
NetBSD would make dhclient work.

Now, I'm running the 1.5.1 release, but nothing has changed.
I'm thinking that the NatSemi chips are still not fixed 100%, because I
doubt that dhclient would be the problem.
DHCP with my NetGear works fine under Windows 98 SE.

Unlike with your case, my dhclient gives me the same error every time
without
fail and I am never able to ping my router or dns servers or anything on the
cable intranet which I would normally be able to do.  But perhaps between
the two of us, we can make a case for some kind of lingering bug with the
NatSemi DP83815 chip?

Here's the output of my ifconfig before dhclient:

    sip0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> mtu 1500
        address: 00:a0:cc:77:98:1f
        media: Ethernet autoselect (10baseT)
        status: active

And after I run dhclient (albeit unsuccessfully):

    sip0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        address: 00:a0:cc:77:98:1f
        media: Ethernet autoselect (10baseT)
        status: active
        inet 203.45.200.101 netmask 0xfffffe00 broadcast 255.255.255.255
        inet6 fe80::2a0:ccff:fe77:981f%sip0 prefixlen 64 scopeid 0x1

(where 203.45.200.101 is the fixed IP address, because I cannot get one
assigned via dhclient for obvious reasons.  It is the IP address currently
leased
to me under windows, where everything works fine.)

My Machine is an AMD Athlon Thunderbird 1000mhz on an Abit KT7A
mainboard. Ethernet is NetGear FA311 10/100 Fast Ethernet (DP83815 chip).

I know this doesn't really help either of us, but at least we are
experiencing
the same problem, which may lead to a clearer picture of what's going on.
Any thoughts, replies, suggestions, please don't hesitate to reply.