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List:       dhcp-client
Subject:    Re: Client id option
From:       "David W. Hankins" <David_Hankins () isc ! org>
Date:       2004-11-23 18:07:24
Message-ID: 20041123180724.GJ12782 () isc ! org
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On Mon, Nov 22, 2004 at 06:08:43PM -0800, Subhash Gopinath wrote:
> interface eth0 {
>         send dhcp-client-identifier "00:0D:9D:5D:C3:41";
> }

That should send that string, but I doubt it's what you want.

there's no point in setting the client identifier to the mac address.
You may as well just let the server use the source mac...and besides,
that's not the encoding commonly used, so if you're trying to match
another operating system's unwisely formulated client identifier,
you've got it wrong anyhow:

	send dhcp-client-identifier "\x01\x00\x0D\x9D\x5D\xC3\x41";

Those are hex escapes, which is easiest when encoding a mac address.
This actually produces the mac addres sin binary rather than the mac
address as an ASCII string as you had.  The leading 1 defines the
hardware type.

> And here's the TCPDUMP o/p of the command -
> tcpdump -n -vvv -i eth0 -XX proto \\udp and port 67 and ether src
> 00:0D:9D:5D:C3:41
> 
> 18:03:58.126698 IP (tos 0x10, ttl  16, id 0, offset 0, flags [none],
> proto 17, length: 328) 0.0.0.0.bootpc > 255.255.255.255.bootps:
> BOOTP/DHCP, Request from 00:0d:9d:5d:c3:41, length: 300,
> xid:0x35c0b13, flags: [none] (0x0000)
>           Client Ethernet Address: 00:0d:9d:5d:c3:41 [|bootp]
>         0x0000:  ffff ffff ffff 000d 9d5d c341 0800 4510  .........].A..E.
>         0x0010:  0148 0000 0000 1011 a996 0000 0000 ffff  .H..............
>         0x0020:  ffff 0044 0043 0134 69aa 0101 0600 035c  ...D.C.4i......\
>         0x0030:  0b13 0000 0000 0000 0000 0000 0000 0000  ................
>         0x0040:  0000 0000 0000 000d 9d5d c341 0000 0000  .........].A....
>         0x0050:  0000 0000 0000 0000 0000 0000 0000 0000  ................
> 
> As you can see, DHCP options are not in the packet ... Any idea why
> this is happenning ?

I can't, you only provided a tiny part of the DHCP header, up to and
including the SNAME field.

(hints: length: 328, 0x0050 is only 80 in decimal, so that's only 96
bytes dumped).

tcpdump grabs 68 by default, 96 on some systems where that's the actual
minimum (I thought that was only sunos tho).

Anyway, increase your snaplen (-s 768 to tcpdump) if you want to see
the client identifier.

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