Re: [spring] WGLC - draft-ietf-spring-srv6-network-programming

["Ketan Talaulikar (ketant)" <[e-mail]>]

Hi Sasha,

Please check inline below.

From: Alexander Vainshtein <[e-mail]>
Sent: 04 March 2020 15:41
To: Ketan Talaulikar (ketant) <[e-mail]>
Cc: [e-mail]; Martin Vigoureux <[e-mail]>; Joel M. Halpern <[e-mail]>; Andrew G. Malis <[e-mail]>
Subject: RE: [spring] WGLC - draft-ietf-spring-srv6-network-programming


Ketan,

Lots of thanks for the pointer.



Here is the text I have found at this reference:



4.4<https://tools.ietf.org/html/draft-ietf-lsr-isis-srv6-extensions-06#section-4.4>.  Maximum End D MSD Type





   The Maximum End D MSD Type specifies the maximum number of SIDs in an

   SRH when performing decapsulation associated with "End.Dx" behaviors

   (e.g., "End.DX6" and "End.DT6") as defined in

   [I-D.ietf-spring-srv6-network-programming<https://tools.ietf.org/html/draft-ietf-lsr-isis-srv6-extensions-06#ref-I-D.ietf-spring-srv6-network-programming>].



   SRH Max End D Type: 45 (Suggested value - to be assigned by IANA)



   If the advertised value is zero or no value is advertised

   then it is assumed that the router cannot apply

   "End.DX6" or "End.DT6" behaviors if the outer IPv6 header contains an SRH.





I assume that you have actually referred to the highlighted text in this section – is this correct?



If this is correct then, to the best of my understanding:

  1.  The request for PSP (expressed as inability to process the SRH and to perform certain lookup by the originator of an SID) is global and not local between the originator and the penultimate node

[KT] This is correct.

  1.  It is not clear what the penultimate router that has received such a request but cannot implement it is supposed to do.

[KT] This is not a request to the penultimate SR Endpoint Node. The source SR Node explicitly instructs the penultimate SR Endpoint Node when it wants it do PSP operation. A router which does not support PSP operation (i.e. does not advertise SIDs with those flavors), then the source SR Node will not be able to instruct it to do PSP. Ultimately the SR Source Node decides.



Thanks,

Ketan



My 2c,

Sasha



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Cell:      [phone]

Email:   [e-mail]<mailto:[e-mail]>





-----Original Message-----
From: Ketan Talaulikar (ketant) <[e-mail]<mailto:[e-mail]>>
Sent: Wednesday, March 4, 2020 11:49 AM
To: Alexander Vainshtein <[e-mail]<mailto:[e-mail]>>; Joel M. Halpern <[e-mail]<mailto:[e-mail]>>; Andrew G. Malis <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]>; Martin Vigoureux <[e-mail]<mailto:[e-mail]>>
Subject: RE: [spring] WGLC - draft-ietf-spring-srv6-network-programming



Hi Sasha,



There is the signalling from the "tail-end node" in SRv6 as well. Perhaps you missed https://clicktime.symantec.com/3Fjd1GocprnmRnQ68mT2Nv46H2?u=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-ietf-lsr-isis-srv6-extensions-06%23section-4.4 ?



Thanks,

Ketan



-----Original Message-----

From: spring <[e-mail]<mailto:[e-mail]>> On Behalf Of Alexander Vainshtein

Sent: 04 March 2020 15:09

To: Joel M. Halpern <[e-mail]<mailto:[e-mail]>>; Andrew G. Malis <[e-mail]<mailto:[e-mail]>>

Cc: [e-mail]<mailto:[e-mail]>; Martin Vigoureux <[e-mail]<mailto:[e-mail]>>

Subject: Re: [spring] WGLC - draft-ietf-spring-srv6-network-programming



Joel, Andy and all,

FWIW I concur with your positions regarding comparison between PHP in MPLS and PSP in SRv6.



I would also like to stress that, to the best of my understanding,  in MPLS PHP is a local behavior between the penultimate and ultimate nodes with the ultimate node explicitly requesting it and the penultimate one giving the option to agree (i.e.to pop the top label when forwarding the packet) or disagree (and to swap the top label to Explicit NULL). The head-end node (and the rest of the nodes on the path) remain completely ignorant of this behavior. I.e., PHP has been introduced - and remains - truly optional.



I have not seen any specifications that would allow the tail-end node of an SRv6 path that wants to benefit from PSP to explicitly request this behavior from the penultimate one, nor do I see would the penultimate node that cannot support PSP do if requested to perform it.  The suggestions I have seen that it would be up to the head-end node (that inserts the SRH) to indicate that PSP is requested - on behalf of the tail-end node? -  look problematic to me as well.



My 2c,

Regards,

Sasha



Office: [phone]

Cell:      [phone]

Email:   [e-mail]<mailto:[e-mail]>



-----Original Message-----

From: spring <[e-mail]<mailto:[e-mail]>> On Behalf Of Joel M. Halpern

Sent: Wednesday, March 4, 2020 9:09 AM

To: Andrew G. Malis <[e-mail]<mailto:[e-mail]>>

Cc: [e-mail]<mailto:[e-mail]>; Martin Vigoureux <[e-mail]<mailto:[e-mail]>>

Subject: Re: [spring] WGLC - draft-ietf-spring-srv6-network-programming



In this case, it is even less relevant.  The PSP for SRv6 does not remove the double-processing.  It merely removes the need to ignore the SRH at the ultimate node.



Yours,

Joel



On 3/3/2020 6:27 PM, Andrew G. Malis wrote:

> MPLS PHP was invented to solve a particular issue with some forwarding

> engines at the time - they couldn't do a final pop followed by an IP

> lookup and forward operation in a single forwarding cycle (it would

> impact forwarding speed by 50% best case). 20 years later, is this

> still an issue at the hardware/firmware level? If so, affected

> implementers should speak up, otherwise there's really no need for PSP.

>

> Cheers,

> Andy (who was there at the time)

>

> On Tue, Mar 3, 2020 at 3:11 PM Robert Raszuk <[e-mail]

> <mailto:[e-mail]>> wrote:

>

>     Hi Ron,

>

>      >   MPLS PHP is a clear case of de-encapsulation.

>

>     Purely looking at technical aspect that is not true at all.

>

>     MPLS PHP does not remove label stack. MPLS PHP is just used to pop

>     last label. After MPLS PHP packets continue with remaining label

>     stack to the egress LSR (example L3VPN PE).

>

>      >  I don't think that you can compare MPLS PHP with SRv6 PSP

>

>     But I agree with that. Both operations have very little in common

>     from packet's standpoint or forwarding apect. Well maybe except

>     "penultimate" word :)

>

>     Kind regards,

>     R.

>

>

>     On Tue, Mar 3, 2020 at 8:30 PM Ron Bonica

>     <rbonica=[e-mail]

>     <mailto:[e-mail]>> wrote:

>

>         Folks,

>

>         I don't think that you can compare MPLS PHP with SRv6 PSP. MPLS

>         PHP is a clear case of de-encapsulation. We do that all the

>         time. In SRv6 PSP, we are removing something from the middle of

>         a packet. That is quite a different story.

>

>

>

>                Ron

>

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> https://clicktime.symantec.com/3HYxrbBRUMaCG5VTr1FEMZ96H2?u=https%3A%2<https://clicktime.symantec.com/3HYxrbBRUMaCG5VTr1FEMZ96H2?u=https%3A%252>

> F%2Fwww.ietf.org%2Fmailman%2Flistinfo%2Fspring

>



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