Re: [tsvwg] design assumptions - draft-ietf-udp-options

[Tom Herbert <[e-mail]>]

On Tue, Jul 16, 2019 at 5:31 PM Joe Touch <[e-mail]> wrote:
>
> Getting back to the core design assumptions:
>
> 1- support options
> 2- allow at least some options to be silently ignored by legacy receivers (to enable ‘“optionally enhanced” exchanges)
> 3- allow at least some options to be required
> 4- allow the options themselves to be protected
> 5- support for fragmentation/reassembly
> 6- support for MTU discovery
> 7- support (optional?) middlebox checksum/payload length bug traversal
> 8- support LITE, i.e., where some of the payload is not covered by at least some checksum processing
>
> AFAICT:
>
> #7 requires a CCO-like sum, but it MUST he calculated AFTER all other options are populated (it depends on the value of ALL other options and surplus data)
>
> #8 can depend on everything except CCO (it doesn’t need to protect CCO), but it depends on the value of all other options and needs to be computed next-to-last (or last if CCO isn’t present)
>
> And we need a way to know:
>         - for #7, whether CCO is included or not used (at user’s peril, but to allow for transmitters to avoid work)
>         - for #8, when to end the options (either a length field OR a EOL flag)
>
> Are there any other design requirements?
>

- Method to disambiguate legacy uses of surplus space
- Specification for options negotiation
- Denial of Service mitigations
- Fallback mechanism to use when intermediate devices drop packets
with UDP surplus space
- Extensibility, i.e. something like version number for the protocol
- Protocol headers versus protocol trailers
- Implementation and deployment considerations
   - Integration into a host stack
   - Interaction with common accelerations for UDP
   - Middleboxes interactions (particularly guidelines for protocols
suggested in https://datatracker.ietf.org/meeting/104/materials/slides-104-wgtlgo-forwarding-plane-realities-00)
   - Running code that implements UDP option to evaluate and guide
above. Preferably open source in Linux since that is the most deployed
end host OS that would support UDP options


> Joe
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