[dhcwg] DHCPv4

Does the value in "maximum message size" option (option code 56) include 
the IP and UDP headers?

Neither RFC2131 or RFC2132 ever state this explicitly, but they are 
self-consistent if it's the case. RFC2132 states that the minimum legal 
value is 576 octets, which equals IP header + UDP header + fixed DHCP 
fields + the minimum 312 octet options field specified in RFC2131.

I ask because I've just come across a client which advertises a maximum 
message size of 548. Presumably this is broken, and there's a chance 
that the client is also misinterpreting a "576" maximum message size 
option _from_ a DHCP server  and could potentially try and use 28 bytes 
that the server cannot receive.

If the wise ones here can confirm that this really is an RFC violation, 
I'll submit a bug report to the vendor of the client.

Cheers,

Simon.

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[dhcwg] DHCPv4 - definition of maximum message size.