Re: More on iSCSI boot

[Glen Turner <glen.turner@aarnet.edu.au>]

Black_David@emc.com wrote:
> 
> David Robinson's messages support my inclination to reuse
> DHCP option 17 (Root Path) by defining iSCSI syntax
> for it.

The "root path" is still useful if the image
has been loaded using iSCSI or TFTP.

An alternative would be to request an option for
"image load protocol" and redefine DHCP's "sname"
and "file" and options 66 "Server name" and option
67 "bootfile name" for interpretation with iSCSI.

Without an allocated option, it might be possible
to simply redefine the sname/66 and file/67 so
that sname/66 beginning with "iscsi:" defines
the iSCSI boot method.


GENERAL COMMENTS ON DRAFT-02

I'm not at all keen on the mechanism in draft-*-boot-02.
The DHCP option should be more generic, as in

  <bootprotocol>:<bootpath>

and defined for iSCSI as

  iscsi:<servername>[:<protocol>[:<port>[:<lun>[:<wwui>]]]]

This would limit future options growth.

Even better would be to define a DHCP option "boot protocol"
and reuse the sname/66 and file/67 fields.  In the absence
of the "boot protocol" option TFTP would be assumed.

Other issues with the draft:

 - if <servername> is a domain name then
     - the "name server" DHCP option SHOULD
       be provided
     - <servername> SHOULD be a FQDN unless
       the "domain name" option DHCP option
       is provided

 - <protocol> may be better to be textual, as
   this allows variants on TCP (such as framing).
   Default value is "tcp" with "tcp-*", "udp" and
   "sctp" intended for future use.  Syntax is:

      <protocol> ::= <lowerstring>
                 ::= <null>
      <lowerstring> ::= <plchar>
               ::= <string><plchar>
      <plchar> ::= <punctuation>
               ::= <lchar>
      <punctuation> ::= - | .
      <lchar> ::= a | b | ... | z

The syntax of all textual options should be defined using
IETF BNF rather than in the text.

 - The "LUN" field is a 16 byte hexadecimal
   representation of the 8-byte LU number in hex.

   does not allow for SCSI to redefine or expand
   the LUN.  Although this is unlikely, I'd suggest 
   text like:

   <LUN> is the SCSI logical unit number in hexadecimal.
   The syntax is:

      <LUN> ::= <hexoctet>
            ::= <LUN><hexoctet>
      <hexoctet> ::= <hexdigit><hexdigit0>
      <hexdigit0> ::= 0 | 1 | ... | 9 | A | B | ... | F | a | b | ... | f
      <hexdigit> ::= <hexdigit0> | <null>

   If you do want a fixed-length field, then using BNF
   can replace the somewhat unwieldy text

      <lunoption> ::= :<lun> | <null>
      <lun> ::= <hex1><hex1><hex1><hex1><hex1><hex1><hex1><hex1>
      <hex1> ::= <hexdigit><hexdigit>
      <hexdigit> ::= 0 | 1 | ... | 9 | A | B | ... | F | a | b | ... | f

-- 
 Glen Turner                                 Network Engineer
 (08) 8303 3936      Australian Academic and Research Network
 glen.turner@aarnet.edu.au          http://www.aarnet.edu.au/
--
 The revolution will not be televised, it will be digitised