Re: [spring] A technical concern regarding draft-schmutzer-spring-cs-sr-policy-00

[Robert Raszuk <[e-mail]>]

Hi Sasha,


   1. > Activate multi-topology IGP (e.g., MT-ISIS, RFC 5120
   <https://datatracker.ietf.org/doc/html/rfc5120>)


Don't you still run default topology which could suffer in the very same -
and a very valid issue - you are reporting ?

- - -

The biggest issue for me for this proposal is that it highlights how to
accomplish egress soft queuing reservation without any real time checks and
automated operational measurements/feedback including auto terminating the
service if operational assumptions are not met.

Yes we do not have such a feedback model translated into service operations
adopted in IETF but we are neither proposing circuit switching over
connectionless paradigm.

We are used to the notion that it is better to deliver degraded service
then no service which IMO does not hold when it comes to guaranteed
delivery promise.

Thx,
Robert

On Thu, Jun 15, 2023 at 3:54 PM Alexander Vainshtein <
[e-mail]> wrote:

> Christian and all,
>
> I have read Section 3.1 of the latest available version of the draft
> <https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-02#section-3.1>,
> and it seems that the BW guarantee mechanisms proposed in this section rely
> on some mechanisms that prevent non-CS traffic from stealing resources from
> the CS-SR Policies in all cases including such unplanned events as
> activation of TI-LFA paths following link failure and/or activation of
> micro-loop avoidance paths following, say, link recovery.
>
>
>
> There seems to be no way to guarantee that this mechanisms would be
> actually deployed and used correctly.
>
>
>
> IMHO and FWIW a clean and “pure SR” solution (at least for SR-MPLS) can be
> provided along the following lines:
>
>    1. Activate multi-topology IGP (e.g., MT-ISIS, RFC 5120
>    <https://datatracker.ietf.org/doc/html/rfc5120>)
>    2. Configure a certain non-default topology on all the interfaces that
>    you expect to use for CS-RS policies, and:
>       1. Allocate the required resources (BW etc.) for this topology on
>       each link where it is defined
>       2. Request MT-ISIS to advertise Adj-SIDs for this topology (in
>       addition to whatever is advertised for the default topology), and take care
>       that packets received with the labels allocated for these adjacencies are
>       forwarded using the topology-specific resources
>    3. Report multi-topology configuration and Adj-SIDs to the SDN
>    controller and instruct it to build CS-SR Policies from Adj-SIDs belonging
>    to the SC-SR topology.
>
>
>
> Your feedback would be highly appreciated.
>
>
>
> Regards,
>
> Sasha
>
>
>
> *From:* Christian Schmutzer (cschmutz) <[e-mail]>
> *Sent:* Tuesday, May 2, 2023 7:29 PM
> *To:* Dongjie (Jimmy) <[e-mail]>
> *Cc:* Christian Schmutzer (cschmutz) <[e-mail]>; Alexander
> Vainshtein <[e-mail]>;
> [e-mail]; [e-mail]
> *Subject:* [EXTERNAL] Re: A technical concern regarding
> draft-schmutzer-spring-cs-sr-policy-00
>
>
>
> Hi Dongjie,
>
>
>
> As long as traffic of a CS-SR policy is within the “bandwidth contract”
> established during the CS-SR policy instantiation (or last update) I don’t
> see any issue with resource competition.
>
>
>
> Cases where a CS-SR policy is “out of contract” we tried to address so far
> with those two sentences
>
> *https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-01#section-3.1-6
> <https://clicktime.symantec.com/15siQpeisyPpFpXcXd89A?h=QFoPsVQa-vRttLx1U4FMJVlNfX7oOWNTtn7GXokENHk=&u=https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-01%23section-3.1-6>*
>
> *https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-01#section-7.3-3
> <https://clicktime.symantec.com/15siVer1Lb5QfmMY5BXHn?h=oQjT6Rcm1EY8Zb3gB2lANSSC4BXWoMyuZiyYj1mD174=&u=https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-01%23section-7.3-3>*
>
>
>
> Packet bursts of course are a different story, but do equally apply to
> RSVP-TE and MPLS-TP/GMPLS and I don’t think have been explicitely discussed
> in respective documents there? Having said that we can think of expanding
> on
> https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-01#section-3.1-3.1
> <https://clicktime.symantec.com/15siKzTSRMiDqshgz4izY?h=BTGVvXgC4AaxgRce4XH1qR7Qa6oeiGHW7JcUQzx_6bM=&u=https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-01%23section-3.1-3.1> and
> discuss how policer burst values and network interface queue limits can be
> tuned to accomodate for bursts.
>
>
>
> I would propose to incorporate potential changes in the future, or do you
> see final text for these topics gating WG adoption call?
>
>
>
> regards
>
> Christian
>
>
>
> On 28.04.2023, at 10:58, Dongjie (Jimmy) <[e-mail]> wrote:
>
>
>
> Hi Christian,
>
>
>
> Thanks for updating the draft and reminding me about my comments on the
> previous version.
>
>
>
> I’ve gone through the text in section 3.1, and think it describes useful
> approaches for providing bandwidth guarantee to CS policies. While I have
> one remaining question:
>
>
>
> My reading is that the bandwidth is allocated to all the CS SR policies
> (either via a physical link, a logical link or a queue), this could ensure
> the total bandwidth of all the CS policies are guaranteed. While since
> different CS policies share the same set of resources, is it possible that
> in some cases the services carried by the CS policies may compete with each
> other for that set of shared resources (e.g. due to burst in some CS
> services)? If so, do you want to mention this in the draft, and may also
> provide some approaches to avoid or mitigate this effect.
>
>
>
> Best regards,
>
> Jie
>
>
>
> *From:* Christian Schmutzer (cschmutz) [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* Thursday, April 27, 2023 6:37 PM
> *To:* Dongjie (Jimmy) <[e-mail]>; Alexander Vainshtein <
> [e-mail]>
> *Cc:* Christian Schmutzer (cschmutz) <[e-mail]>;
> [e-mail]; [e-mail]
> *Subject:* Re: A technical concern regarding
> draft-schmutzer-spring-cs-sr-policy-00
>
>
>
> Dear WG,
>
>
>
> As we are preparing for WG adoption call, could you please let us know if
> the concerns have been addressed?
>
>
>
> Thanks in advance
>
> Christian
>
>
>
>
> On 15.02.2023, at 19:24, Christian Schmutzer (cschmutz) <
> [e-mail]> wrote:
>
>
>
> Hi Jie and Sasha,
>
>
>
> We recently published a new version of the draft trying to address your
> concerns on assumptions and procedures for guaranteeing bandwidth for CS-SR
> policies in the following section *https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-01#name-ensuring-bandwidth-guarante
> <https://clicktime.symantec.com/15siFAG9xk2dRvsmSWKqv?h=Xh2pyKVkbcPM9xX055CHed6lCPfVTAYEYm2YzmNDNVo=&u=https://datatracker.ietf.org/doc/html/draft-schmutzer-spring-cs-sr-policy-01%23name-ensuring-bandwidth-guarante>*
>
>
>
> Probably not perfect but wondering what you think? Further input and
> discussion is welcome !
>
>
>
> regards
>
> Christian
>
>
>
>
> On 26.07.2022, at 22:23, Dongjie (Jimmy) <[e-mail]> wrote:
>
>
>
> Hi Sasha and Christian,
>
>
>
> To my understanding the potential services of CS-SR require some level of
> performance guarantee, which means the traffic needs to be distinguished
> from other traffic in the network and be treated separately. As discussed
> in this thread, one approach would be to steer the traffic to a separate
> queue or a separate set of resources.
>
>
>
> I agree with Sasha that requesting a dedicated traffic class may not be
> easy. Sasha gave a mechanism based on the coexistence of MPLS-TP and
> SR-MPLS. An alternative to that would be to use a separate set of SR SIDs
> for the CS-SR, and associate such set of SR SIDs with a separate set of
> network resources (e.g. sub-interfaces or queue). That could be achieved by
> using resource-aware SIDs as defined in
> draft-ietf-spring-resource-aware-segments.
>
>
>
> Best regards,
>
> Jie
>
>
>
> *From:* Pce [mailto:[e-mail] <[e-mail]>] *On
> Behalf Of *Alexander Vainshtein
> *Sent:* Tuesday, July 26, 2022 3:48 PM
> *To:* Christian Schmutzer (cschmutz) <[e-mail]>
> *Cc:* [e-mail]; [e-mail];
> Rotem Cohen <[e-mail]>; Nitsan Dolev <[e-mail]>;
> [e-mail]; Michael Gorokhovsky <[e-mail]>
> *Subject:* Re: [Pce] A technical concern regarding
> draft-schmutzer-spring-cs-sr-policy-00
>
>
>
> Christian,
>
> Lots of thanks for your prompt response to my concerns about the SR-CS
> Policy draft.
>
> Unfortunately I will not be able to attend the SPRING session later today
> (even remotely).
>
>
>
> Regarding your explanation, I believe that the key point is the sentence “*everything
> not running over CS-SR has no bandwidth guarantee, is of lower priority and
> can undergo packet drops during DiffServ PHB processing*”.
>
>
>
> This statement is an *assumption* that:
>
> 1.  Is critical for SR-CS to deliver its promise
>
> 2.  Is actually a requirement (and quite a strong one) for the operator
> of the SR network to enforce strict separation of traffic that uses SR-CS
> and all the rest of traffic to different traffic classes. Implementing this
> requirement in a live operational network may be quite a non-trivial
> operation
>
> 3.  Unless I am mistaken, is not explicitly stated in the current version
> of the draft (or in any of the associated drafts),
>
>
>
> At the same time, I agree that, if this assumption holds, SR-CS can
> deliver its promise.
>
>
>
> Please notice also that in the  case of MPLS networks the same results can
> be achieved with MPLS-TP running as “ships in the night” with SR-MPLS but
> without the overhead of deep label stacks required by SR-CS. This approach
> has been developed and deployed for quite some time now. IMHO it would be
> interesting to compare these two approaches.
>
>
>
> Regards,
>
> Sasha
>
>
>
> Office: [phone]
>
> Cell:      [phone]
>
> Email:   [e-mail]
>
>
>
> *From:* Christian Schmutzer (cschmutz) <[e-mail]>
> *Sent:* Monday, July 25, 2022 6:45 PM
> *To:* Alexander Vainshtein <[e-mail]>
> *Cc:* Christian Schmutzer (cschmutz) <[e-mail]>;
> [e-mail]; [e-mail]; Rotem
> Cohen <[e-mail]>; Nitsan Dolev <[e-mail]>;
> [e-mail]; Michael Gorokhovsky <[e-mail]>
> *Subject:* [EXTERNAL] Re: A technical concern regarding
> draft-schmutzer-spring-cs-sr-policy-00
>
>
>
> Hi Sasha,
>
>
>
> Many thanks for reviewing draft-schmutzer-pce-cs-sr-policy
> (draft-schmutzer-spring-cs-sr-policy) and sharing your input / concerns.
> Let me try to address them.
>
>
>
> CS-SR policies don’t require additional unprotected adj-SIDs. The
> unprotected adj-SID part of the two adj-SIDs you mentioned typically being
> present per link in a network does suffice.
>
>
>
> Further the draft does not assume bandwidth guarantees for those
> unprotected adj-SIDs. Bandwidth is managed by the PCE at a link level and
> bandwidth guarantees are achieved by ensuring that the total amount
> of bandwidth requested by all candidate-paths going via a link is kept
> below the reservable maximum bandwidth defined.
>
>
>
> To ensure a link is never congested by just CS-SR traffic, end-to-end
> path-protection and restoration is used. This ensures traffic does only
> flow along a path (working, protect or restore) for which bandwidth
> admission control has been done during path establishment.
>
>
>
> You are correct, mechanisms such as TI-LFA may lead to congestion, but the
> assumption is that everything not running over CS-SR, has no bandwidth
> guarantee, is of lower priority and can undergo packet drops during
> DiffServ PHB processing.
>
>
>
> There are many ways to fulfil those PHB processing requirements. One way
> is to mark CS-SR policy traffic with a unique EXP/DSCP and map it into a
> dedicated priority queue. CS-SR traffic may share a EXP/DSCP and/or queue
> with other traffic if the operate is certain that the queue will never be
> congested (i.e. the non CS-SR traffic is important but has very low volume
> and the queue’s bandwidth is over-provisioned to be enough for CS-SR and
> non CS-SR traffic together)
>
>
>
> I will take the action on thinking about how some more / better text could
> be added to the draft without being to specific to limit deployment
> choices.
>
>
>
> Hopefully the above does provide a bit more clarity. I am happy to discuss
> more, fyi I will present the draft in the SPRING WG session, but will be
> attending IETF114 online only.
>
>
>
> Regards
>
> Christian
>
>
>
>
>
> On 24.07.2022, at 19:02, Alexander Vainshtein <
> [e-mail]> wrote:
>
>
>
> Hi all,
>
> I would like to clarify that, from my POV, my technical concerns about
> draft-schmutzer-pce-sr-cs-routing-policies
> <https://clicktime.symantec.com/15t5ZrUvivrzY8sT1ijxH?h=oARDBH4W-5ffeLBR147jEqYwP_rR1J1Akb38blbagcY=&u=https://datatracker.ietf.org/doc/html/draft-schmutzer-pce-cs-sr-policy-02>
>  presented in my email dated 11-Jul-22
> <https://clicktime.symantec.com/15t5eggDBYYax5hNZH96u?h=SF8xdDZrlCfJegvv79QramWDaqy05gg48KBreJtvyuM=&u=https://mailarchive.ietf.org/arch/msg/spring/ctrAx6JFaNwLhMCQB5QUdBCR7B8/>
>  fully apply to this draft.
>
>
>
> Specifically, the authors do not define any mechanisms that would prevent
> possible usage of unprotected Adj-SIDs used in the configuration of the
> candidate paths of CR-CS policies from being also used by such well-known
> and widely deployed mechanisms as TI-LFA and Segment Routing Microloop
> Avoidance.  As a consequence, the “strict BW guarantees”  that are expected
> of SR-CS policies would be violated every time one of these mechanisms
> would result in some “regular” traffic being sent via the paths defined by
> such mechanisms.
>
>
>
> Even if such mechanisms were defined in a future version of
>  draft-schmutzer-spring-cs-sr-policy, a retrofit of existing
> implementations of TI-LFA and/or SR Microloop Avoidance would be required.
>
>
>
> I understand the motivation for CR-SC Policies, but I strongly suspect that
>  *SR cannot be used as a replacement for MPLS-TP* when it comes to BW
> guarantees.
>
>
>
> Regards,
>
> Sasha
>
>
>
> Office: [phone]
>
> Cell:      [phone]
>
> Email:   [e-mail]
>
>
>
>
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