Re: [tsvwg] New Version Notification for draft-herbert-udp-space-hdr-01.txt

[Tom Herbert <[e-mail]>]

On Wed, Jul 10, 2019 at 12:24 PM Joe Touch <[e-mail]> wrote:
>
>
>
>
>
> On 2019-07-10 11:36, Tom Herbert wrote:
>
>
> ...
> The UDP surplus header provides alignment,
>
>
> UDP options already has NOPs for that.
>
The NOPs align the options to the start of surplus. If the surplus
space is unaligned to begin with then there's no point to using NOPs
to align individual options.

>
> integrity check,
>
>
> UDP options already has a OCS for that.

A one byte optional checksum is next to useless as an integrity check.
This has already been brought up in reference to OCS.

>
>
> disambiguation for other uses of surplus space,
>
>
> This isn't needed. It won't support existing uses (not that any are known) because they won't follow the format.  UDP options already allows for experimental uses and other standards-track extensions through codepoint assignment.

If the checksum fails then surplus space isn't processed. So,
probability of misinterpretation of some random use of surplus space
is < 0.0015%.

>
>
> a means to extend the UDP header,
>
>
> Actually, it hinders UDP options by limiting them to 1020 bytes, as with all "other uses".
>
That is intentional. Allowing unlimited options is a path towards DOS attack.

>
> friendliness with HW and SW implentations,
>
>
> It has no benefit vs. the existing approach in this regard.
>
The checksum ensures that the surplus space sums to zero so that the
UDP checksum computation yields the same result rather it covers the
UDP datagram only or the UDP datagram and surplus space. If we don't
have this property, we will lose checksum offload which is important
for UDP performance. Along similar lines, a per packet checksum is
much better than the fragmentation checksum since we can offload the
former and not the latter.

Tom