Re: [spring] Suggest some text //RE: Request to close the LC and move forward//RE: WGLC - draft-ietf-spring-srv6-network-programming

[神明達哉 <[e-mail]>]

At Sat, 29 Feb 2020 12:06:17 +0100,
Robert Raszuk <[e-mail]> wrote:

> Even if RFC8200 section 4 text would say:
>
>  "Extension headers cannot be added to a packet after it has left its
> source node and extension headers cannot be removed from a packet until it
> has arrived at its ultimate destination".
>
> PSP would be still not be violating anything said in this sentence. Reason
> being is that we are dealing here with an *encapsulated* packet which has
> as its ultimate destination SR node X. That SR node X is to perform or not
> PSP. So it is still fully compliant with the specification.

(Sorry for the hopefully small delay, I've been out of town for these
several days and am now catching up with the backlog).

Hmm, so, using the notation shown in Section 5.1 of
draft-ietf-spring-srv6-network-programming-10, is this how the PSP is
expected to work?

- Node N creates an encapsulated IPv6 packet:
  (T, S1) (S3, S2, S1; SL=2) (A, B2)
- at S1, since SL != 0,
  decrease SL to 1,
  copy SList[SL] = SList[1] = S2 to the destination address of the
  IPv6 header, so we now have:
  (T, S2) (S3, S2, S1; SL=1) (A, B2)
- at S2, since SL != 0,
  decrease SL to 0
  copy SList[SL] = SList[0] = S3 to the destination address of the
  IPv6 header, so we now have:
  (T, S3) (S3, S2, S1; SL=0) (A, B2)
  according to Section S14 of draft-ietf-spring-srv6-network-programming-10.
- Now we apply Section 4.16.1 (PSP).
  Since SL == 0 at this point, Payload length and next header value
  are adjusted, RH is removed, and we now have:
  (T, S3) (A, B2)

It's not clear what will happen next from the text of
draft-ietf-spring-srv6-network-programming-10, but is presumably it as
follows?
- The packet will be forwarded to S3
- At S3, since it's the (ultimate) destination of the outper IPv6
  packet, it decapsulates the packet, and we now have:
  (A, B2)
- The decapsulated packet is forwarded towards B2

--
JINMEI, Tatuya