[Dnsmasq-discuss] Setting BOOTP "magic cookie"

Simon Kelley simon at thekelleys.org.uk
Sun Sep 6 21:31:54 BST 2009

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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