[dhcwg] Review of DNA draft

["Joel M. Halpern" <joel@stevecrocker.com>]

Bernard Aboba requested a "SIR" review of the
Detection of Network Attachment (DNA) in IPv4 internet draft
<http://www.drizzle.com/~aboba/DNA/draft-ietf-dhc-dna-ipv4-01.txt>.
I have read the document and have the comments below.

My apologies if my concerns have been discussed on the mailing list already 
and resolved.  I reviewed the document and the issues page (and the ARP 
RFC) in preparing this.

I hope this review is of assistance to your work.
Joel M. Halpern


Over all the draft is well written and clear.  It is on the right track, 
but I believe it could use some clarifications.  In particular, two aspects 
seem to me to be in need of assistance.

Firstly, the problem statement seems to be missing a piece.  While the 
concern being addressed is likely obvious to those who work daily with DHCP 
and DHCP related issues, it is not obvious to a reader from another 
community.  In particular, I found myself asking why I would use the 
reachability validation step rather than simply going directly to 
INIT-REBOOT state and sending a DHCPREQUEST to the broadcast address.  I 
suspect that the ARP reachability verification mechanism is expected to be 
significantly faster and to place less load on other parts of the 
system.  But the document does not say that.

Secondly, in the description of the reachability verification mechanisms it 
would be helpful if there were a sentence indicating why the use of the 
0.0.0.0 source protocol address will be effective.  (I checked the ARP RFC< 
not having ARP code handy, and I understand that the ARP response 
generation sends the response to the source hardware address.  It would be 
helpful to the reader if the document said this.)  Related to this 
clarification, it would probably be helpful to note (probably in an 
appendix) both whether this behavior has been observed to cuase any strange 
ARP cache entries and whether most observed implementations do indeed 
respond properly to the message proposed here.  (I know they 
should.  However, the difference between theory and practice...)



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