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

Gyan Mishra <hayabusagsm@gmail.com> Tue, 03 March 2020 16:26 UTC

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From: Gyan Mishra <hayabusagsm@gmail.com>
Date: Tue, 3 Mar 2020 11:25:45 -0500
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To: "Darren Dukes (ddukes)" <ddukes@cisco.com>
Cc: "6man@ietf.org" <6man@ietf.org>, Bob Hinden <bob.hinden@gmail.com>, "Xiejingrong (Jingrong)" <xiejingrong@huawei.com>, "spring@ietf.org" <spring@ietf.org>, =?UTF-8?B?56We5piO6YGU5ZOJ?= <jinmei@wide.ad.jp>
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Subject: Re: [spring] Suggest some text //RE: Request to close the LC and move forward//RE: WGLC - draft-ietf-spring-srv6-network-programming
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I read the updated version 11 and the verbiage looks very good and provides
all the necessary clarity in the process.

https://tools.ietf.org/html/draft-ietf-spring-srv6-network-programming-11#section-4.16.1

For 6MAN in terms of RFC 8200 as Brian Carpenter mentioned and noticed in
assistance in adding to the latest verbiage it really helped.

The key is that to the PSP node the incoming SL is 1 - but after the final
DA is copied the SL pointer is updated so  the outgoing SL is 0  - this
satisfying the pseudocode criteria and RFC 8200 to remove the SRH since the
final DA is now set.


If you look at this before the packet is received then it appears as in
flight and not final destination so it may appear not in RFC 8200
conformance which has been the contention all along.  However,  if you look
at it after PSP node has received and processed the PSP function psuedocode
you are now in RFC 8200 conformance.


Kind regards

Gyan


On Tue, Mar 3, 2020 at 10:18 AM Darren Dukes (ddukes) <ddukes@cisco.com>
wrote:

> Hi Jingrong, I notified Gyan yesterday that the version he was reviewing
> was over a year old.
> I expect when Gyan reviews the current version it should clear up any
> lingering questions.
>
> Darren
>
> On Mar 3, 2020, at 1:34 AM, Xiejingrong (Jingrong) <xiejingrong@huawei.com>
> wrote:
>
> Hi Gyan,
> What revision are you reading ?
> I found the 4.21.1 only in its very early revision (-00 and -01).
> There is only 4.16 and the PSP is introduced in 4.16.1 in the latest draft
> is rev-11 :
> https://tools.ietf.org/html/draft-ietf-spring-srv6-network-programming
> And I think the explanation of “A penultimate SR Segment Endpoint Node” in
> the latest rev is helpful to understand better:
>    SR Segment Endpoint Nodes receive the IPv6 packet with the
>    Destination Address field of the IPv6 Header equal to its SID
>    address.  A penultimate SR Segment Endpoint Node is one that, as part
>    of the SID processing, copies the last SID from the SRH into the IPv6
>    Destination Address and decrements Segments Left value from one to
>    zero.
>
> Thanks
> Jingrong
>
> *From:* Gyan Mishra [mailto:hayabusagsm@gmail.com <hayabusagsm@gmail.com>]
>
> *Sent:* Tuesday, March 3, 2020 12:52 PM
> *To:* Xiejingrong (Jingrong) <xiejingrong@huawei.com>
> *Cc:* 6man@ietf.org; Bob Hinden <bob.hinden@gmail.com>om>; spring@ietf.org;
> 神明達哉 <jinmei@wide.ad.jp>
> *Subject:* Re: Suggest some text //RE: [spring] Request to close the LC
> and move forward//RE: WGLC - draft-ietf-spring-srv6-network-programming
>
>
> Hi Jingrong
>
> I am following what you displayed and it makes sense. In section 4.21.1
> for the PSP flavor what was confusing was it said that the End.X with PSP
> flavor can pop the SRH.  The way it’s written,  to me it reads that any P
> router can pop the SRH when the last SID is written to the DA. So if the
> SRH SID list happens to not steer to the egress PE and ended a few hops
> early,  and If PSP is true then the SRH could be popped early on any P
> node.  Maybe I am reading to far into the verbiage.  I think since End.X
> could be any P transit router what I am saying could happen.
>
> 4.21.1
> <https://tools.ietf.org/html/draft-filsfils-spring-srv6-network-programming-07#section-4.21.1>.
> PSP: Penultimate Segment Pop of the SRH
>
>
>
>
>
>    After the instruction 'update the IPv6 DA with SRH[SL]' is executed,
>
>    the following instructions must be added:
>
>
>
>  1.   IF updated SL = 0 & PSP is TRUE
>
>  2.      pop the top SRH                                         ;; Ref1
>
>
>
>
>
>
>
>
>
>    Ref1: The received SRH had SL=1.  When the last SID is written in the
>
>    DA, the End, End.X and End.T functions with the PSP flavour pop the
>
>    first (top-most) SRH.  Subsequent stacked SRH's may be present but
>
>    are not processed as part of the function.
>
>
> At each hop each node copies the SID to DA and updates the SL = SL -1
>
> I am depicting an incoming SL value to each node and then each node
> updates the SL pointer along the path hop by hop.
>
> PSP mode
>
> CE1----[PE1----{SL=2} - P2--{SL=1} -P3--pop--PE4]----CE2
>
> PSP disabled (USP)
>
> CE1----[PE1----{SL=2} - P2--{SL=1} -P3---{SL=0}--PE4 pop]----CE2
>
> USD  (USD) - Decapsulation & forward native packet payload to customer CE
>
> CE1----[PE1----{SL=2} - P2--{SL=1} -P3---{SL=0}--PE4 dencap]----CE2
>
> Thanks
>
> Gyan
>
> On Sun, Mar 1, 2020 at 7:59 PM Xiejingrong (Jingrong) <
> xiejingrong@huawei.com> wrote:
>
> Hi Gyan,
> In my understanding, PSP is used right in a P node, works for both End and
> End.X ( I haven’t known End.T very well yet).
>
> Suppose:
> CE1----[PE1----P2----P3----PE4]----CE2
> PE1 encapsulation the customer packet with an outer IPv6 header and an
> SRH, the packet arriving P2 will be:
> (SA=PE1, DA=P2<End>) (SL=2, PE4<End.DT4>, P3<End.X>, P2<End>)
>  (customer-packet)
>
> Then, the packet arriving P3 will be:
> (SA=PE1, DA=P3<End.X>) (SL=1, PE4<End.DT4>, P3<End.X>, P2<End>)
>  (customer-packet)
>
> In Non-PSP mode, the packet will be sent to PE4 like this:
> (SA=PE1, DA=PE4<End.DT4>) (SL=0, PE4<End.DT4>, P3<End.X>, P2<End>)
>  (customer-packet)
>
> In PSP mode, the packet will be sent to PE4 like this:
> (SA=PE1, DA=PE4<End.DT4>) (customer-packet)
>
> For you assumption, “Since every PE in an SR domain both SRv6 or SR-MPLS
> identical to MPLS would be both a SR source node and final destination node
> of an LSP.”
> I don’t think that’s always true, you can find an example I was recently
> thinking about in another mail:
> VM----TOR----Spine----Superspine----[PE1----P2----P3----PE4]----subscribers.
> Even if it is true for some network, the capability to handle the SRH on a
> receiving packet is different than the encapsulation of an outer IPv6
> header with an SRH header.
> Sending (with encapsulation) and receiving (with
> recognizing/processing/demultiplexing),  they are not necessarily the same
> ---- like the things to fragment and assembly.
> A PE may be well capable of encapsulation everything (like BFD template),
> but may fail to process a little thing that it is unrecognized.
>
> It may just drop any packet with Next Header value other than 4/41/47/etc.
>
> It may send such packet with any routing header to its slow-path for the
> compliance but lose the necessary performance.
>
> Thanks
> Jingrong
>
> *From:* Gyan Mishra [mailto:hayabusagsm@gmail.com]
> *Sent:* Monday, March 2, 2020 4:20 AM
> *To:* Xiejingrong (Jingrong) <xiejingrong@huawei.com>
> *Cc:* 6man@ietf.org; Bob Hinden <bob.hinden@gmail.com>om>; spring@ietf.org;
> 神明達哉 <jinmei@wide.ad.jp>
> *Subject:* Re: Suggest some text //RE: [spring] Request to close the LC
> and move forward//RE: WGLC - draft-ietf-spring-srv6-network-programming
>
>
> Hi Jingrong,
>
>
> Can you help provide some clarification on the use cases for PSP flavor
> with end.X and end.T functions.
>
> Under Ref1 where it mentions end.X and end.T functions to use PSP knob  as
> well if desired.
>
> How would that work with any P node using the PSP function?
>
>
> https://tools.ietf.org/html/draft-filsfils-spring-srv6-network-programming-07#section-4.21
>
>
>
> 4.21.1
> <https://tools.ietf.org/html/draft-filsfils-spring-srv6-network-programming-07#section-4.21.1>.
> PSP: Penultimate Segment Pop of the SRH
>
>
>
>
>
>    After the instruction 'update the IPv6 DA with SRH[SL]' is executed,
>
>    the following instructions must be added:
>
>
>
>  1.   IF updated SL = 0 & PSP is TRUE
>
>  2.      pop the top SRH                                         ;; Ref1
>
>
>
> Ref1: The received SRH had SL=1.  When the last SID is written in the
>
>    DA, the End, End.X and End.T functions with the PSP flavour pop the
>
>    first (top-most) SRH.  Subsequent stacked SRH's may be present but
>
>    are not processed as part of the function.
>
>
> Also trying to understand the reason given for PSP function for legacy
> final destination egress PE not being SRv6 capable.
>
> Since every PE in an SR domain both SRv6 or SR-MPLS identical to MPLS
> would be both a SR source node and final destination node of an LSP.  I am
> using the MPLS term LSP with SR as the concept of FEC destination which now
> is a prefix SID still exists that all traffic to egress final destination
>  PE is forwarded to.
>
> Since LSPs built to FEC destination are uni directional as they are with
> MPLS  and that would be the case as well for SR paths - the idea that the
> final destination PE would lack hardware capability for SRH processing does
> not make sense as the source and final destination node are one and the
> same.
>
> Am I missing something?
>
> Kind Regards
>
> Gyan
>
> On Fri, Feb 28, 2020 at 9:14 PM Xiejingrong (Jingrong) <
> xiejingrong@huawei.com> wrote:
>
> Got it.
> Thanks for your clarification of your point.
>
> Jingrong
>
> -----Original Message-----
> From: 神明達哉 [mailto:jinmei@wide.ad.jp]
> Sent: Saturday, February 29, 2020 9:28 AM
> To: Xiejingrong (Jingrong) <xiejingrong@huawei.com>
> Cc: Ted Lemon <mellon@fugue.com>om>; Pablo Camarillo (pcamaril) <
> pcamaril@cisco.com>gt;; Brian E Carpenter <brian.e.carpenter@gmail.com>om>; Bob
> Hinden <bob.hinden@gmail.com>om>; Joel M. Halpern <jmh@joelhalpern.com>om>;
> spring@ietf.org; 6man@ietf.org
> Subject: Re: Suggest some text //RE: [spring] Request to close the LC and
> move forward//RE: WGLC - draft-ietf-spring-srv6-network-programming
>
> At Fri, 28 Feb 2020 07:54:28 +0000,
> "Xiejingrong (Jingrong)" <xiejingrong@huawei.com> wrote:
>
> > The design of PSP for the benefits of deployment is based on the
> > understanding that it does not violate section 4 of RFC8200. In case
> > the RFC8200 text may be modified in the future, the PSP may also need to
> change accordingly.
>
> No, it violates Section 4 of RFC8200.  It's a pity that we have to discuss
> it at this level due to the poor editorial work then (I was also
> responsible for that as one of those reviewing the bis draft), but anyone
> who involved the discussion should know the intent of this text intended to
> say (borrowing from Ron's text) "Extension headers cannot be added to a
> packet after it has left the its source node and extension headers cannot
> be removed from a packet until it has arrived at its ultimate
> destination".  It might look "an attempt of blocking an innovation by a
> small group of vocal fundamentalists", but if you see the responses without
> a bias, you'd notice that even some of those who seem neutral about the
> underlying SRv6 matter interpret the text that way.
>
> I'd also note that simply because PSP violates RFC8200 doesn't immediately
> mean it (PSP) "needs to change".  It can update RFC8200 with explaining why
> it's necessary and justified.  That's what I requested as you summarized:
>
> > Jinmei: it should say it updates this part of RFC8200 and explain why
> it's justified.
>
> And, since PSP at least wouldn't break PMTUD, I guess the update proposal
> will have much more chance to be accepted than a proposal including EH
> insertion.  On the other hand, pretending there's no violation will
> certainly trigger many appeals and objections at the IETF last call (I'll
> certainly object to it).  In the end, it can easily take much longer, or
> even fail, than formally claiming an update to RFC8200.
>
> --
> JINMEI, Tatuya
> --------------------------------------------------------------------
> IETF IPv6 working group mailing list
> ipv6@ietf.org
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> --------------------------------------------------------------------
>
> --
> Gyan  Mishra
> Network Engineering & Technology
> Verizon
> Silver Spring, MD 20904
> Phone: 301 502-1347
> Email: gyan.s.mishra@verizon.com
>
>
>
> --
> Gyan  Mishra
> Network Engineering & Technology
> Verizon
> Silver Spring, MD 20904
> Phone: 301 502-1347
> Email: gyan.s.mishra@verizon.com
>
>
> _______________________________________________
> spring mailing list
> spring@ietf.org
> https://www.ietf.org/mailman/listinfo/spring
>
>
> --

Gyan  Mishra

Network Engineering & Technology

Verizon

Silver Spring, MD 20904

Phone: 301 502-1347

Email: gyan.s.mishra@verizon.com