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Date:      Sat, 03 Aug 2002 20:00:57 -0400
From:      Andy Sparrow <spadger@best.com>
To:        "Bri" <brian@ukip.com>
Cc:        freebsd-stable@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG
Subject:   Re: dhcp problems with my ISP 
Message-ID:  <20020804000057.BA7AB43@CRWdog.demon.co.uk>
In-Reply-To: Message from "Bri" <brian@ukip.com>  of "Sat, 03 Aug 2002 11:12:12 BST." <NEBBKKNOEKKNLLNMEOHFAEBFIKAA.brian@ukip.com> 

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--==_Exmh_-1265239676P
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> Hi I have a Cable and have a Cable Modem for my internet connection of which
> you use dhcp to obtain an IP address great but this only seems to work
> successfully on a Windows machine I've registered all the other mac
> addresses of unix boxes and Apple macs I have and they seem to have alot of
> difficulty obtaining IP addresses. Especially the UNIX machines which run
> FreeBSD 4.5-RELEASE or 5.0-CURRENT on sparc64 at the moment the sparc64 box
> which is a Sun Ultra 5 which is the worst for detecting an IP with dhclient.

On that hardware, you may be experiencing issues with auto-negotiation on the 
"Happy Meal" ethernet. Try nailing it to a fixed port speed, this may help. Or 
not.

My Ultra-1 Just Will Not Work with some network devices, it is perfectly happy 
with others. Link link is not a reliable indicator. Sad but true.

> What I would really like to know is what does the windows dhcp do
> differently than say dhclient.

Not much - most of what it does differently is due to the different ways in 
which you can interpret the protocol spec. However, note that almost all 'Doze 
DHCP clients behave differently to each other. Heh.

See the RFC's for details, I think 2143 is the main one. "The DHCP Handbook" 
is well worth the money too. The ISC DHCP lists are searchable, and are 
frequently invaluable.

> I would be very interested to know as I would like a UNIX machine that can
> maintain and IP address.

I've used my FreeBSD laptop with DHCP on many, many different networks, 
running ISC v2, many flavours of v3, M$ DHCP server, Lucent QIP to name a few 
over the last ~3 years, and I've never seen any issues with any of them where 
the server itself was functional (and I'd remembered to appropriately set the 
local firewall ;-).

It maintains an IP just fine, except on networks where they have address churn 
on the DHCP server (usually due to lack of IPs in the pool).

Try plugging a hub between the modem and the external interface of the 
firewall and sniff the DHCP exchanges on another machine (you don't need an IP 
address to sniff packets) - this may not show the whole picture, in particular 
it won't show what's being sent out the WAN end of the modem, but it's a start.

If the DHCPNAK/DHCPACK packets aren't getting to the client (or bootp, 
DHCPREQ, DHCPINFORM etc. to the server), it can't ever work.

If the server responds to a bootp/DHCP packet from the client, it's a 
reasonable assumption that it's seeing at least part of the traffic generated.

Power cycle the modem, plug in the 'Doze box, repeat.

Cheers,

AS



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