DHCP is a layer 3 technology that talks directly to layer 2.
This is entirely acceptable, useful and right for NETWORK configuration. DHCP
is an entirely sensible means of obtaining an IP address and _proposals_ for
domain name prefixes and DNS servers.
DHCP should not be used for any other purpose. In particular to make use of
DHCP for application configuration is a layer violation. Layer 7 should NEVER
communicate with Layer 2 directly. When that happens we lose all the power and
flexibility built into the IP stack.
To give a concrete example of the problems caused. I am currently typing on a
VeriSign machine in an office in VeriSign corporate HQ. In that environment the
local DHCP server could provide me with useful and valid suggestions for all
manner of services. But its still the wrong technology.
The problem is that when I take the machine to the Hilton Garden Inn down the
road where I am staying I explicitly DO NOT want the hotel network to provide
any more than an IP address. I am not going to use their DNS server and I
certainly don't want to make use of any email server, DNS prefix, GEOPRV or any
other application layer feature they might want to foist onto me.
I am using the Hilton Garden Inn LAN, I am not joining their network. The
machine is remaining on the VeriSign network.
DHCP is a fine technology for the task DHCP is designed to do. It is an
inappropriate technology for application or service configuration. The proper
infrastructure to support those needs is DNS, supplemented if necessary by HTTP
or LDAP backing store (i.e. either discover the services via DNS directly or
use DNS to discover where the directory service is to be found).
Looking at the history of UPnP and Zero Config it strikes me that attempting to
manage networks through peer to peer broadcast or multicast have been a bust
precisely because of this layer violation.
-----Original Message-----
From: James M. Polk [mailto:jmpolk(_at_)cisco(_dot_)com]
Sent: Thursday, April 19, 2007 5:31 PM
To: Dawson, Martin; John Schnizlein; Andrew Newton
Cc: GEOPRIV WG; ietf(_at_)ietf(_dot_)org; Allison Mankin
Subject: RE: [Geopriv] Confirmation of GEOPRIV IETF 68
Working Group Hums
At 04:20 PM 4/19/2007, Dawson, Martin wrote:
"DHCP is not adequate because it doesn't meet multiple sets of
requirements as documented multiple times ..."
bologna
"documented multiple times" means in individual submissions
of which, zero facts were presented to substantiate
If DHCP were so inadequate, why is the DSL forum now going to
specify it? Why does PacketCable define it? These were
fairly recent moves...
And, how many times has HELD been presented as if it were a
product of an IETF WG?
James
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