Subject: Re: [tsvwg] Comments on recent UDP options work

From: "C. M. Heard" <[email-masked]>
Date: Mon, 18 Feb 2019 21:45:33 -0800

On Sun, Nov 25, 2018 at 12:33 PM C. M. Heard <[email-masked]> wrote:
> The attraction that I see for FRAG as a UDP-Option is that it offers
> incremental deployability in the important case of DNS (and probably in
> some other cases as well). Its use can be negotiated on a
> transaction-by-transaction basis. The negotiation signal from a client
> that supports it (use of a null FRAG option in a request) will be ignored
> by a legacy server. And an upgraded server will not use the option unless
> the client negotiates it. So, upgraded client can talk to a legacy server,
> and a legacy client can talk to an upgraded server, without the
> need to introduce any extra protocol exchanges.

I see that dnsop recently declined to adopt the ATR (Additional Truncated
Response) draft as a fix for paths on which IP fragmentation does not work.
See https://mailarchive.ietf.org/arch/msg/dnsop/pvUGkBzd0D8Y9p6y020XXvxvr58
and related messages. The problem remains unsolved. One of the respondents
said "i would prefer to embrace fragmentation and fix it," which would be
ideal if it is possible; but barring that, the best proposal that I have
seen UDP fragmentation along the lines described in the udp-options draft.

Mike Heard