Re: [tsvwg] Alternative version of the UDP FRAG option

["C. M. Heard" <[e-mail]>]

On Sat, Mar 16, 2019 at 9:06 AM Tom Herbert wrote:
> Thinking about this, it occurs to me be that the LITE option isn't
> needed. The assumption in the UDP options draft is that a receiver
> needs the UDP payload to immediately follow the UDP header, but the
> UDP payload can be anywhere in the surplus area as long as it's
> aligned to four bytes. A receiver will know how to handle it and
> deliver the UDP data to the application (e.g. by maintaining a pointer
> to the data).
>
> So that allows a format like:
>
> UDP header (Length=8) | Surplus area header | Options | Payload
>
> The surplus area header contains the header length and a checksum
> covering the surplus space (four bytes altogether). The three headers
> can thought of as an extended UDP header, so the format becomes:
>
> Extended UDP header | Payload
>
> Which looks a whole lot like any other protocol format with a variable
> length header such as TCP or IPv4.

A major downside to this approach is that is does not let you add
"optional to process" options such as MSS, Echo Request, and Echo
Response to UDP datagrams that are intended to be processed normally
by legacy receivers that do not understand UDP options or the extended
UDP header format. You can do that with the option trailer as
currently proposed.

Mike Heard