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

Robert Raszuk <robert@raszuk.net> Wed, 04 March 2020 13:31 UTC

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From: Robert Raszuk <robert@raszuk.net>
Date: Wed, 4 Mar 2020 14:31:03 +0100
Message-ID: <CAOj+MME2tW3UstHgfQap1fqH2miJL7=8mUEVz_Rm6--oTN670g@mail.gmail.com>
To: "Ketan Talaulikar (ketant)" <ketant@cisco.com>
Cc: Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>, "spring@ietf.org" <spring@ietf.org>
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Subject: Re: [spring] WGLC - draft-ietf-spring-srv6-network-programming
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Hi Ketan,

So essentially you are confirming that subject to topology in worst case I
need to double the flooding amount of SIDs in my network to support both
PSP and non PSP operation. I think if we would consider PSP as optional or
on-demand behaviour we could architect it without the need for double
flooding node's SIDs just to indicate in one PSP=0 and in the other one PSP
!=0 (which by itself is still subject to given IGP and SR code even
allowing you to do that).

Thx,
R.

On Wed, Mar 4, 2020 at 12:01 PM Ketan Talaulikar (ketant) <ketant@cisco.com>
wrote:

> Hi Robert,
>
>
>
> Please check inline below.
>
>
>
> *From:* Robert Raszuk <robert@raszuk.net>
> *Sent:* 04 March 2020 16:07
> *To:* Ketan Talaulikar (ketant) <ketant@cisco.com>
> *Cc:* Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>om>;
> spring@ietf.org
> *Subject:* Re: [spring] WGLC - draft-ietf-spring-srv6-network-programming
>
>
>
>
>
> Hi Ketan,
>
>
>
> Let's assume following scenario:
>
>
>
>                       ----- T1
>
>                      |
>
> A ----  Z ----  P ---- T2
>
>                     |
>
>                       ----- T3
>
>
>
>
>
> A - is ingress
>
> P - is potential PSP performer
>
> Ts - are egress (from SR pov)
>
>
>
> Q1:
>
>
>
> Assume T1 and T3 signal capability to handle SRH depth = 4 and T2 = 2
>
> Assume P signals PSP = 5 for SID P
>
> SRH depth required is 3
>
>
>
> How does A can build SRH for all three SR paths to do PSP only to node T2
> ?
>
>
>
> sub-Q1:  Is it legal today to signal by P two SIDs one with PSP depth
> supported = N and the other with depth = 0 ?
>
> *[KT] The MSD support is advertised at node level. The node P can
> advertise say two End SID – one with PSP and another without it. The SR
> Source Node picks up which of the two End SIDs to pick based on the
> capabilities of the egress nodes. Ultimately, the SR Source Node A decides
> and instructs P what it needs to do for each of the 3 paths.*
>
>
>
> Q2:
>
>
>
> Assume T1, T2 and T3 signal capability to handle SRH depth = 4
>
> Assume P signals PSP = 5 for SID P
>
> SRH depth required is 3
>
>
>
> How can A build SRH such that PSP will happen only for very fat flows ?
>
> *[KT] As in the previous example, A can make a choice on a per flow basis
> by picking up the PSP or non-PSP flavor of P’s SIDs.*
>
>
>
> Q3:
>
>
>
> Assume T1, T2 and T3 signal capability to handle SRH depth = 2
>
> Assume P signals PSP = 0
>
> SRH depth required is 3
>
>
>
> Would A not be able to insert SRH and do any SR in this case ?
>
> *[KT] Yes, A cannot generate a packet with SRH with 3 segments destined to
> the T nodes in such a case.*
>
>
>
> *Thanks,*
>
> *Ketan*
>
>
>
> Many thx,
>
> R.
>
>
>
>
>
>
>
>
>
> On Wed, Mar 4, 2020 at 11:17 AM Ketan Talaulikar (ketant) <ketant=
> 40cisco.com@dmarc.ietf.org> wrote:
>
> Hi Sasha,
>
>
>
> Please check inline below.
>
>
>
> *From:* Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>
> *Sent:* 04 March 2020 15:41
> *To:* Ketan Talaulikar (ketant) <ketant@cisco.com>
> *Cc:* spring@ietf..org <spring@ietf.org>rg>; Martin Vigoureux <
> martin.vigoureux@nokia.com>gt;; Joel M. Halpern <jmh@joelhalpern.com>om>;
> Andrew G. Malis <agmalis@gmail.com>
> *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
>
>
>
> Office: +972-39266302
>
> Cell:      +972-549266302
>
> Email:   Alexander.Vainshtein@ecitele.com
>
>
>
>
>
> -----Original Message-----
> From: Ketan Talaulikar (ketant) <ketant@cisco.com>
> Sent: Wednesday, March 4, 2020 11:49 AM
> To: Alexander Vainshtein <Alexander.Vainshtein@ecitele.com
> <Alexander.Vainshtein@ecitele..com>>; Joel M. Halpern <jmh@joelhalpern.com>om>;
> Andrew G. Malis <agmalis@gmail.com>
> Cc: spring@ietf.org; Martin Vigoureux <martin.vigoureux@nokia.com>
> 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 <spring-bounces@ietf..org <spring-bounces@ietf.org>> On
> Behalf Of Alexander Vainshtein
>
> Sent: 04 March 2020 15:09
>
> To: Joel M. Halpern <jmh@joelhalpern.com>om>; Andrew G. Malis <
> agmalis@gmail.com>
>
> Cc: spring@ietf.org; Martin Vigoureux <martin.vigoureux@nokia.com>
>
> 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: +972-39266302
>
> Cell:      +972-549266302
>
> Email:   Alexander.Vainshtein@ecitele.com
>
>
>
> -----Original Message-----
>
> From: spring <spring-bounces@ietf..org <spring-bounces@ietf.org>> On
> Behalf Of Joel M. Halpern
>
> Sent: Wednesday, March 4, 2020 9:09 AM
>
> To: Andrew G. Malis <agmalis@gmail.com>
>
> Cc: spring@ietf.org; Martin Vigoureux <martin.vigoureux@nokia.com>
>
> 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 <robert@raszuk.net
>
> > <mailto:robert@raszuk.net <robert@raszuk.net>>> 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=40juniper.net@dmarc.ietf.org
>
> >     <mailto:40juniper.net@dmarc.ietf.org <40juniper.net@dmarc.ietf.org>>>
> 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
>
> >
>
> >     _______________________________________________
>
> >     spring mailing list
>
> >     spring@ietf.org <mailto:spring@ietf.org <spring@ietf.org>>
>
> >
>
> > 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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