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

[Raffaele Zullo <[e-mail]>]

Hello,

On 2019-03-12 16:36, C. M. Heard wrote:
> On Tue, Mar 12, 2019 at 3:09 AM Joe Touch wrote:

> A revised OCS (that includes the pseudo-header correction) will allow
> FRAG **without** LITE (as proposed in the draft) to traverse the
> affected middleboxes with a non-zero UDP CS, but that method has the
> following downsides:
> 
> 1) A legacy host interprets FRAG without LITE as a complete UDP 
> datagram
> 2) The same is true for an options-aware host if OCS fails
> 3) There is duplicate checksum coverage (UDP checksum covers each 
> fragment,
>    plus post-reassembly checksum contained in the terminal FRAG option)

This is true, but
1 can be solved if FRAG Option has a 2 bytes Length and carries the 
fragment inside it.
2 if the fragment is inside FRAG and OCS is not valid, the fragment is 
just discarded
3 covering each fragment with OCS is basically the same of covering the 
reassembled packet

> 
> AFAICT, forcing the revised OCS to cover the data in each fragment
> provides protection that is essentially equivalent to that provided
> by the proposed post-reassembly checksum.  ...

> Mike Heard

You actually already pointed out 3
and already suggested The FRAG Option carrying fragment inside 
previously.


Thank you,
Raffaele Zullo