Re: [Spud] updated draft PLUS charter, rev. 1 June

[Joe Touch <[e-mail]>]

On 6/7/2016 3:19 PM, Tom Herbert wrote:
> On Tue, Jun 7, 2016 at 3:09 PM, Joe Touch <[e-mail]> wrote:
>>
>> On 6/7/2016 3:05 PM, Tom Herbert wrote:
>>> The proper architectural solution is to place network layer
>>> information like what is being proposed in the network layer :-)
>>> Trying to make a network layer out of UDP fails on several accounts
>>> (fragments don't contain UDP headers, ports do not have global
>>> meaning, etc.). IPv6 extension headers are designed for carrying
>>> information like this, I really hope there is more investigation as to
>>> whether they are workable for signaling.
>> It depends on what layer is actually doing the signaling. If it's
>> on-path, I agree - that's network layer and should be somewhere besides
>> the transport header. If'it's on-path but not from the endpoint it also
>> begs the question of whether IP packet headers should be extended
>> in-transit (I made the case long ago that this was valid for IPv6 but I
>> think someone is working to close that loophole or already has).
>>
> There has been a long discussion in 6man for 2460bis as to whether
> IPv6 extension headers can be added by middelboxes. The consensus
> seems to be that is it not allowed primarily because such actions
> change the size of the packet and hence mess up PMTU discovery. I
> would think this rationale must apply if devices are allowed to change
> UDP payload in flight. Devices should never increase the size of a
> packet, if they wish to add information to a packet for transit across
> one network then encapsulation is a good alternative.

Encapsulation doesn't magically solve the PTMU problem.

The only solution is to reserve space - e.g., for the IPv6 header to
have included "NOP" or other variants of reserved space that can be
overwritten.

UDP payloads should NEVER be modified in flight. Only the end system or
its designee should ever do so. I sincerely hope we end up assuming DTLS
or some such to ensure that this is the case.

Joe