Subject: Re: Naive philosophy question: What distinguishes DHCP from

From: Kim Kinnear <[email-masked]>
Date: Tue, 6 Apr 1999 11:49:22 -0400 (EDT)

Radia,

The pragmatic answer to the question "How can you tell when
a packet is DHCP vs BOOTP?" is that a packet is DHCP
if and only if it contains a dhcp-message-type option (option
code 53).  This option defines the packet not only as a
DHCP packet, but also determines which type of DHCP packet
it is.

Many (most?) DHCP servers today also support one or more
varieties of BOOTP, and they determine that an input packet
is a BOOTP packet by the absence of the dhcp-message-type
option.

Cheers -- Kim

At 09:00 PM 4/5/99 -0400, Radia Perlman - Boston Center for Networking wrote:
>To me, DHCP looks just like another version of BOOTP. I originally
>thought DHCP was when the "vendor specific" field got redefined
>as a true "options" field with registered options values.
>But then someone pointed out the RFC that defined the use of
>the vendor specific field for BOOTP, which came out several years
>after BOOTP. So my original theory (that you can tell it's DHCP
>because of the magic cookie) is wrong, since BOOTP used the same cookie value.
>
>I know DHCP does dynamic leasing of addresses and BOOTP doesn't.
>
>But it's backward compatible with BOOTP.
>
>So how would you answer when a naive person asks "what's the difference
>between DCHP and BOOTP?
>
>How can you tell when a packet is DHCP vs BOOTP? Is it just if it contains
>options not defined early enough (before BOOTP got renamed DHCP?) Or
>is it really a meaningless question, and there's no reason to be able
>to tell whether a packet is one or the other?
>
>Thanks,
>
>Radia
>