Subject: [dhcwg] Submission of an errata for RFC 4436 Section 2.1.1

From: Bernard Aboba <[email-masked]>
Date: Fri, 24 Nov 2006 19:04:04 -0800 (PST)

We have discovered an errata in RFC 4436 Section 2.1.1 and would like DHC 
WG approval to submit it to the RFC Editor. 

The paragraph that is in error reads as follows:

   "If a valid ARP Reply is received, the MAC address in the sender
   hardware address field (ar$sha) in the ARP Reply is matched against
   the target hardware address field (ar$tpa) in the ARP Request, and
   the IPv4 address in the sender protocol address field (ar$spa) of the
   ARP Reply is matched against the target protocol address field
   (ar$tpa) in the ARP Request.  If a match is found, then the host
   continues to use that IPv4 address, subject to the lease re-
   acquisition and expiration behavior described in Section 4.4.5 of the
   DHCP specification [RFC2131]."

The first problem is that ar$tpa is not the target hardware address; 
however, a larger issue is that the address being tested for is not 
ar$tha, but rather than MAC address of the node being tested (ar$tha is 
zero in the ARP request anyway). 

Stuart Cheshire has suggested that for maximum clarity, we submit an 
errata to change the paragraph to the following:

   "If a valid ARP Reply is received, where:
   
   (a) the address in the sender hardware address field (ar$sha) is
       the MAC address of the node being tested for, and
   (b) the address in the sender protocol address field (ar$spa) is
       the IPv4 address of the node being tested for,

   then the host concludes that its candidate IPv4 address is valid
   for this network and may continue to be used, subject to the lease
   re-acquisition and expiration behavior described in Section 4.4.5
   of the DHCP specification [RFC2131]."

Are there any objections? 

---------- Forwarded message ----------
Date: Tue, 26 Sep 2006 17:53:52 -0700
From: Stuart Cheshire <[email-masked]>
To: Bernard Aboba <[email-masked]>, [email-masked]
Cc: Carlo Bellettini <[email-masked]>
Subject: Re: Submission of an errata for RFC 4436 Section 2.1.1

Bernard Aboba <[email-masked]> wrote:

>"  If a valid ARP Reply is received, the MAC address in the sender
>   hardware address field (ar$sha) in the ARP Reply is matched against
>   the destination MAC address in the ARP Request, and the IPv4
>   address in the sender protocol address field (ar$spa) of the
>   ARP Reply is matched against the target protocol address field
>   (ar$tpa) in the ARP Request."
>
>Does this make sense to you?  Should we file an errata with the RFC 
>Editor? 

Yes, this makes sense, but I'd simply the text even further by removing 
the comparisons to the ARP Request packet altogether. After all, the ARP 
Request packet is not itself the original source of that information; it 
is merely an intermediary, it got it from elsewhere: namely our cached 
data about the node we're testing for.

I'd suggest this:

   If a valid ARP Reply is received, where:

   (a) the address in the sender hardware address field (ar$sha) is
       the MAC address of the node being tested for, and
   (b) the address in the sender protocol address field (ar$spa) is
       the IPv4 address of the node being tested for,

   then the host concludes that its candidate IPv4 address is valid
   for this network and may continue to be used, subject to the lease
   re-acquisition and expiration behavior described in Section 4.4.5
   of the DHCP specification [RFC2131]."

And yes, we should file an erratum.

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

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---

From: Ralph Droms <[email-masked]>
Date: Thu, 30 Nov 2006 13:57:40 -0500

Bernard - I agree with the need for publishing an errata.  While the new
paragraph is significantly changed, it corrects the error and is otherwise
an editorial change to improve clarity.  I think it would be appropriate to
publish the suggested text as an errata.

- Ralph