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

Fernando Gont <> Thu, 27 February 2020 09:07 UTC

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Subject: Re: [spring] Request to close the LC and move forward//RE: WGLC - draft-ietf-spring-srv6-network-programming
To:, "Eric Vyncke (evyncke)" <>, Warren Kumari <>, John Leddy <>
Cc: SPRING WG List <>, "" <>, Bob Hinden <>, "Zafar Ali (zali)" <>
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From: Fernando Gont <>
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Date: Thu, 27 Feb 2020 06:07:14 -0300
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On 27/2/20 05:41, wrote:
> Fernando,
>> -----Original Message-----
>> From: ipv6 [] On Behalf Of Fernando Gont
>> Sent: Thursday, February 27, 2020 12:45 AM
>> Hello, Eric,
>> On 26/2/20 20:18, Eric Vyncke (evyncke) wrote:
>>> Writing this without any hat,
>>> Please note that on the logical side, it still have to be "proven" that this idea is strictly forbidden by RFC 8200.
>> Here's the proof part:
>> 1) Isn't IPv6 end to end?
>> 2) How do core components of IPv6, such as AH and PMTUD work in the
>> present of intermediate nodes that can add and/or remove arbitrary
>> extension headers?
>> It should be clear from the above that EH insertion/deletion is forbidden.
> This draft does not propose that intermediate node add extension header.
>   - If this is not clear to you, please read the draft.

What is this:????

4.16.1.  PSP: Penultimate Segment Pop of the SRH

    The SRH processing of the End, End.X and End.T behaviors are
    modified: after the instruction "S14.  Update IPv6 DA with Segment
    List[Segments Left]" is executed, the following instructions must be
    executed as well:

  S14.1.   If (Segments Left == 0) {
  S14.2.      Update the Next Header field in the preceding header to the
                 Next Header value of the SRH
  S14.3.      Decrease the IPv6 header Payload Length by the Hdr Ext Len
                 value of the SRH
  S14.4.      Remove the SRH from the IPv6 extension header chain
  S14.5.   }

Isn't this having the penultimate segment fo a packet removing an 
extension header for a packet whose Destination Address is not even it's 

Doesn't this read a bit as "the router was the DA of the packet, after 
you change the DA to that of the next waypoint, if you realize Segments 
Left == 0, remove the SRH"?

(which does not even comply with the now infamous "interpretation" of 
RFC8200 that if you are the DA, you can add/remove EHs.

>   - If it's clear, please let's stick to technical comment on _this_ draft. Bringing irrelevant points to the discussion is really not helping (both the discussion  and the argument).
> This draft does not propose that intermediate node add/or remove arbitrary  extension header.
> This draft, and more specifically the PSP flavor [1], is about removing the SRH header by an SR EndPoint.


> - with regards to PMTUD, can you clarify how reducing the size of the packet break PMTUD? And if there is an impact, let's remember that this is the source of the packet which instruct the SR EndPoint to remove the SRH.
> - with regards to AH, the SRH specification explicitly states that the use of SRH with AH by an SR source node is _not_ defined [2]. 

Do you understand that AH should be usable for all IPv6 traffic?

>> (that's what Errata's are for, after all... and it should be clear that
>> the EH processing part, overall, needs improvements).
> Again, thank you for that, I believe this is useful.
> But while this errata is not reviewed and accepted, RFC 8200 stands as is.

The errata is a clarification, not a change. Of course RFC8200 stands: 
EHs are not deleted or added en route to destination.

Fernando Gont
SI6 Networks
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492