Subject: Re: ACCEPT [LL17] Hosts with configured addresses MUST ARP for v4 LL addresses

From: Stuart Cheshire <[email-masked]>
Date: Sun, 23 Feb 2003 13:58:52 -0800

Robert Elz wrote:

>you cannot require ARP, because not all link levels use it.
>The wording needs to be in such a way that specific link level
>technologies are not implied.

Excuse me for stating the obvious:

1.2. Applicability

   The specifications in this document apply to any IEEE 802 media [802]
   including Ethernet [802.3], and other similar link-layer network
   technologies that operate at data rates of at least 1Mb/s, have a
   round-trip latency of at most one second, and support ARP [RFC 826].

   Link-layer network technologies that do not support ARP may be able
   to use other techniques for determining whether a particular IP
   address is currently in use. However, the application of claim-and-
   defend mechanisms to such networks is left to a future document.

Any questions?

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer, Inc.
 * www.stuartcheshire.org

---

From: Robert Elz <[email-masked]>
Date: Tue, 25 Feb 2003 19:07:13 +0700

Date:        Sun, 23 Feb 2003 13:58:52 -0800
    From:        Stuart Cheshire <[email-masked]>
    Message-ID:  <[email-masked]>

  | >you cannot require ARP, because not all link levels use it.
  | >The wording needs to be in such a way that specific link level
  | >technologies are not implied.
  | 
  | Excuse me for stating the obvious:
  | 
  | 1.2. Applicability
  | 
  |    The specifications in this document apply to any IEEE 802 media [802]
  |    including Ethernet [802.3], and other similar link-layer network
  |    technologies that operate at data rates of at least 1Mb/s, have a
  |    round-trip latency of at most one second, and support ARP [RFC 826].
  | 
  |    Link-layer network technologies that do not support ARP may be able
  |    to use other techniques for determining whether a particular IP
  |    address is currently in use. However, the application of claim-and-
  |    defend mechanisms to such networks is left to a future document.
  | 
  | Any questions?

Yes.   The second of those paragraphs implies, strongly, that non-ARP
networks can use LL addresses, and says that how the claim-and-defend
mechanism will operate there will be defined someplace else, some other
time, when it is needed.

That's all fine.

However, this also suggests that the rest of the rules for using LL
addresses, even on non-ARP networks, are specified in this document.

That's good, because this, unless we were to split it into two docs,
one for LL in general, and one for LL on ARPable nets, is where it should be.

There's no reason for them not to be, after all, you wouldn't want the
doc for using LL on X.25 (or ATM without LANE, or something) telling
hosts that they should send packets using LL addresses to a router to
be forwarded (especially as there's no way to know if the router
understands LL or not).

This is actually another issue, that I sent to the list back on Feb 13,
but which Erik hasn't been able to find the time to add to the web page
yet (I assume it will become LL28 eventually).

Look for a message from me, on Feb 13, with the msgid
<[email-masked]> and Subject:
	 New Issue: Applicability of Document

It proposes adding new text to the first para of section 1.2 to clarify
this issue, and make it clear that (aside from address acquisition and
defence, that is ARP issues) the rest of the specification of LL addresses
is in this doc, for all network types.

But the time to discuss that is sometime after the issue gets posted,
and we start on it, rather than now.

kre