[Dnsmasq-discuss] Setting BOOTP "magic cookie"

Tyler Reese tyler.reese at taqua.com
Sun Sep 6 22:32:33 BST 2009

It's a proprietary client that doesn't populate the vendor magic cookie.

A request was made to change the client to just ignore the magic cookie and start parsing vendor options at the 5th byte.  The change could have just as well been to make the client send the magic cookie and then dnsmasq would send it back.  In the end, the same thing is accomplished.

Thanks for the reply,

From: Simon Kelley [simon at thekelleys.org.uk]
Sent: Sunday, September 06, 2009 3:31 PM
To: Tyler Reese
Cc: dnsmasq-discuss at lists.thekelleys.org.uk
Subject: Re: [Dnsmasq-discuss] Setting BOOTP "magic cookie"

Tyler Reese wrote:
> I'm trying to construct a dnsmasq BOOTP reply to match what I am
> getting using the bootp-dd2 server.
> In a wireshark BOOTP trace, it shows a "Magic cookie" attribute which
> are the first 4 bytes of the "Bootp vendor specific options".  When
> using bootpd, I can use 'vm=rfc1084' in the desired entry in
> /etc/bootptab.  This results in the 4 bytes being set to 0x63825363.
> After these 4 bytes, the rest of the options follow...and they are
> decoded in the wireshark packet view.
> Using dnsmasq, what is the equivalent way to set those first 4 bytes
> to 0x63825363?  I am able to set the rest of the following options
> using dhcp-option, but I can't figure out how to set those first 4
> bytes.

This isn't configurable in dnsmasq, from a quick reading of the bootptab
man page, I thing the behaviour is equivalent to vm=auto, ie just echo
back whatever the client sent. For DHCP, client requests which don't
have the correct magic number are dropped, but for BOOTP that check
isn't enforced.

What client are you using?



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