Re: [v6ops] [dhcwg] IPv6-Only Preferred DHCPv4 option

[Tomek Mrugalski <[e-mail]>]

On 04.12.2019 19:36, Bernie Volz (volz) wrote:
> A minor note about the draft requesting use of (DHCPv4) option code 108. Per RFC3679 this was in use as a "swap path" option at some point, though never published as a draft. That is why it is marked as "REMOVED/unassigned" as the idea was to NOT reuse these option numbers until there was a need (i.e., no other just "unassigned" option codes were available). While I have no objection if the draft wishes to request use of that option code, I just wanted to point out that there could be some other conflicting usage out in the wild.

As a person who put that text there, let me explain my reasons. RFC2132
(Mar 1997) said that option codes 128-255 were reserved for
site-specific options. RFC3942 (Nov 2004) reclassified 128-223 as a
general purpose option codes under IANA governance. However, any
implementation created between 1997 and 2004 could have used those
option codes for whatever purpose they desired. It's been quite a long
time ago, but we all know about long tails.

With that in mind, I tried to find the lowest option code that's
available. I was not able to find any specific information about prior
use of codes 102-107, except RFC3679 saying they were returned (and thus
previously used by someone). Code 108 seems safer than other codes - it
is below 128, RFC3679 explicitly says that there was an idea to use it
for swap path, but that must have died quickly if no I-D was ever
published about it. So it seems like a safe bet.

At the end of the day, this is only a request for IANA. If this gets
published, they may honor or ignore it.

Tomek

p.s.
Apologies for sending it today. Museums are supposed to be closed on
Mondays.