Re: [dhcwg] Gratuitous ARP in DHCP vs. IPv4 ACD Draft
Stuart Cheshire <cheshire@apple.com> Thu, 05 August 2004 18:52 UTC
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Subject: Re: [dhcwg] Gratuitous ARP in DHCP vs. IPv4 ACD Draft
Date: Thu, 05 Aug 2004 11:41:50 -0700
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From: Stuart Cheshire <cheshire@apple.com>
To: Ralph Droms <rdroms@cisco.com>
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Cc: DHCP discussion list <dhcwg@ietf.org>, babatke@ra.rockwell.com, Ted Lemon <mellon@nominum.com>
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>If it really doesn't matter, why are we having this discussion? Are >you proposing we change DHCP to use an ARP request for announcements? I don't have any personal reason to want it to be one way rather than the other, but I do believe that a good specification shouldn't leave things unspecified. That means we need to decide whether the document will specify ARP request, or ARP reply. It matters little which it is, but we should decide. I originally assumed that it would be logical to use a gratuitous ARP response, but when I started investigating, it seemed that everyone else thought otherwise. Stevens, "TCP/IP Illustrated, Volume 1: The Protocols" (1994) specifies that hosts announce their new address using a broadcast ARP Request. BSD systems announce their new address using a broadcast ARP Request. Macintosh systems announce their new address using a broadcast ARP Request. Windows systems announce their new address using a broadcast ARP Request. So, despite what RFC 2131 may say, it appears that almost all deployed systems in the field actually use ARP Request. Why? I thought about it and compiled a list of all the reasons for picking one rather than the other (already posted to dhcwg), and found that on balance the evidence came out slightly in favour of using ARP Request (which may explain why that's what all the systems do). In conclusion, (i) the arguments weigh slightly in favour of ARP Request, and (ii) most deployed systems in the field use ARP Request, so that's what I decided to write in the ACD draft. To answer your question, we are having this discussion because this is one of those cases where it's equally possible for an intelligent person to argue either side of the argument. Whichever choice the document picks, there is unfortunately an opposing camp willing to fight indefinitely over the decision. If we change the document, then the other camp becomes willing to fight indefinitely to have it changed back. I'm not proposing that we change DHCP. This draft is not DHCP. This draft is Address Conflict Detection as applied generally to any configuration mechanism, including manual static IP addresses. I'm documenting Address Conflict Detection AS IT EXISTS NOW and has existed for a decade or more. If in future DHCP wants to adopt this standardized Address Conflict Detection mechanism, that's a decision for DHC. Stuart Cheshire <cheshire@apple.com> * Wizard Without Portfolio, Apple Computer, Inc. * www.stuartcheshire.org _______________________________________________ dhcwg mailing list dhcwg@ietf.org https://www1.ietf.org/mailman/listinfo/dhcwg
- Re: [dhcwg] Gratuitous ARP in DHCP vs. IPv4 ACD D… babatke
- Re: [dhcwg] Gratuitous ARP in DHCP vs. IPv4 ACD D… Stuart Cheshire
- Re: [dhcwg] Gratuitous ARP in DHCP vs. IPv4 ACD D… Stuart Cheshire
- Re: [dhcwg] Gratuitous ARP in DHCP vs. IPv4 ACD D… Ralph Droms
- Re: [dhcwg] Gratuitous ARP in DHCP vs. IPv4 ACD D… Stuart Cheshire