Re: Next steps on advancing core IPv6 specifications to full Internet standard

I think this discussion about specific details of specific inserted EHs is
irrelevant.

EH encapsulation vs insertion is as fundamental as whether you believe in
the layered computer networking model or not, where information is added or
removed to PDUs at layer boundaries via encapsulation as they go up and
down the layers, and PDUs are left alone when they travel within a layer
between layer senders and receivers.

It also relates to the difference between what End Systems functions are
and what Intermediate Systems functions are.

Inserting into a previously created PDU, at the same layer, doesn't comply
with that model. It never will regardless of the type of EH inserted,
because insertion is not part of that model.

On 22 Nov. 2016 4:44 am, "Tom Herbert" <tom@herbertland.com> wrote:

>
>
> On Thu, Nov 17, 2016 at 7:33 AM, Hemant Singh <hemantietf@gmail.com>
> wrote:
>
>> On Thu, Nov 17, 2016 at 8:55 AM, Bob Hinden <bob.hinden@gmail.com> wrote:
>>
>>>
>>> There doesn’t seem to be an evidence that there is an interoperability
>>> problem.
>>>
>>>
>> Hemant,
>
>
>> A SR deployment uses source routers from different vendors.  One vendors
>> uses "add an EH header" while another uses the encapsulation method to add
>> the SR info  The intermediate routers have to read the encoded SR
>> instructions for forwarding.  How is the intermediate node instructed to
>> decapsulate and read vs. look at an added EH by the source?  Maybe SR deals
>> with this issue and if so, please let me know which of several SR I-D's
>> cover the details.
>>
>> Rather or not encapsulation is used, the SR EH would be an extension of
> the outermost IP header. Intermediate routers would not be concerned with
> rather the packet is encapsulated except when they are the terminal point
> of the encapsulation (need to decapsulate). So the SR EH is processed the
> same by intermediate nodes whether encapsulation is used or not.
>
> Likewise, Inband OAM has mixed router/switch vendor deployment.  One
>> vendor uses add/delete EH while another uses encap.  How are all
>> routers/switches instructed to use which method?
>>
>> This is inband OAM in an EH or within an encapsulation? If it's in an
> extension header then a similar concept would apply, the EH, presumably a
> HBH option, would need to be set in the outer IP headers so that it is
> processed be intermediate nodes. If an option is writable in then the
> encapsulation might need to copy the information to an EH in the original
> packet if necessary. If the OAM is part of encapsulation then its operation
> would be specified in the encapsulation.
>
>
>> When folks get a chance, could they please also reply to my questions on
>> Inband OAM and SR in earlier emails from today.   It is useful to the
>> mailer to articulate what show stopper problem did one encounter that one
>> could not use encapsulation.   Only once such issues are closed, one can
>> start the other document that would cover pitfalls of add/delete EH by
>> intermediate nodes.
>>
>> Note that the suggestion to use encapsulation is not normative, it does
> not provide exactly the same behavior as inserting EH would (for instance
> ECMP handling would be very different). I think the interaction between EH
> and encapsulation needs to specified as part of the encapsulation, for
> instance the question of what EHs must be copied from the packet being
> encapsulated to the outer packet will need to be addressed.
>
> Tom
>
>
>> Thanks,
>>
>> Hemant
>>
>>
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