Subject: [dhcwg] draft-guo-softwire-sc-discovery-03

From: "Bernie Volz (volz)" <[email-masked]>
Date: Wed, 24 Mar 2010 10:43:17 -0500

Hi:

Regarding your draft, I have two comments regarding the formatting of
options:

3.1. DHCPv4 Softwire Concentrator Discovery (SCD) Option

...

   A DHCP message may carry more than one SCD Option.

Please read http://tools.ietf.org/html/rfc3396 as to why this isn't
valid and won't work with your currently proposed option layout.
Multiple instances of an option in DHCPv4 are CONCATENATED and thus any
encoding that wants 'multiple' instances needs to be formatted that a
single instance contains the option data and is set up in such a way
that it can be decoded as multiple instances.

An easy way to accomplish this would be to add an instance-length byte
before the Tunnel Type field that indicates how long this instance is.
That way, multiple instances can be encoded (code, len, instance1-len,
instance1-data, [instance2-len, instance2-data, [...]]).

Note that in DHCPv6 multiple instances are perfectly valid and are NOT
concatenated.

However, for the DHCPv6 options, suboptions MUST be encoded in DHCPv6
option format. This means 16-bit suboption code, 16-bit suboption
length. Please do NOT define yet another format for clients and servers
to support - DHCPv6 uses 16-bit fields.

- Bernie

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From: Brian E Carpenter <[email-masked]>
Date: Thu, 25 Mar 2010 05:24:44 +1300

Thanks Bernie, very helpful.

Regards
   Brian Carpenter