Re: [spring] SRv6 BGP based Overlay Services (draft-ietf-bess-srv6-services-07)

Robert Raszuk <robert@raszuk.net> Tue, 20 July 2021 10:27 UTC

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From: Robert Raszuk <robert@raszuk.net>
Date: Tue, 20 Jul 2021 12:27:30 +0200
Message-ID: <CAOj+MMHzXL5miTB6UCd0Pe9QUHpDMJatY==PWas9=ke28pAmbw@mail.gmail.com>
To: "UTTARO, JAMES" <ju1738@att.com>
Cc: Shraddha Hegde <shraddha=40juniper.net@dmarc.ietf.org>, "spring@ietf.org" <spring@ietf.org>, "bess@ietf.org" <bess@ietf.org>
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Subject: Re: [spring] SRv6 BGP based Overlay Services (draft-ietf-bess-srv6-services-07)
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Jim,

The "policy" I had in mind was a simple cfg switch "fallback global" for
any SRv6 service originally set to say run over different IGP topology. Or
perhaps if more then two options are available, list the chain of
forwarding tables/topologies to be used as transport for a given SRv6
service.

Implementation may get even smarter and allow operator to set performance
based triggers to select such forwarding topologies from a flat pool.

If Shraddha has the same in mind not sure there is much to elaborate on
here :)

Best,
R.

On Tue, Jul 20, 2021 at 12:20 PM UTTARO, JAMES <ju1738@att.com> wrote:

> *Comments In-Line..*
>
>
>
> *Thanks,*
>
> *              Jim Uttaro*
>
>
>
> *From:* spring <spring-bounces@ietf.org> *On Behalf Of *Shraddha Hegde
> *Sent:* Tuesday, July 20, 2021 5:56 AM
> *To:* Robert Raszuk <robert@raszuk.net>
> *Cc:* spring@ietf.org; bess@ietf.org
> *Subject:* Re: [spring] SRv6 BGP based Overlay Services
> (draft-ietf-bess-srv6-services-07)
>
>
>
>
>
> Good to know the intention is to support fallback for Srv6.
>
>
>
> The way current text is written, it implies service SID is always in the destination address.
>
> And hence service SID should be resolvable. This is not the case when a service SID
>
> Corresponding to flex-algo wants to fallback on best effort services. The destination address cannot carry
>
> Service SID for fallback cases and hence it need not be resolved.
>
>
>
> I suggest that the authors add below text in bold to the draft.
>
>
>
>
>
> “When providing best-effort connectivity *or flex-algo connectivity* to the egress PE,
>
> the ingress PE encapsulates the payload in an outer IPv6 header where the destination
>
> address is the SRv6 Service SID associated with the related BGP route update.
>
>  Therefore, the ingress PE SHOULD perform resolvability check for the SRv6 Service SID
>
>  before considering the received prefix for the BGP best path computation.
>
> “
>
> “*In some cases a service prefix intending to use flex-algo paths may want fallback on*
>
> *best effort paths when a flex-algo path isn’t available. The fallback behavior *
>
> *SHOULD be governed by local policies.   *
>
> *[Jim U>] It would be helpful to provide an example of local policies and how would/should said local policies be applied across a heterogeneous network.*
>
> *The destination address SHOULD contain the best-effort locator based END SID *
>
> *of the egress PE and the SRH SHOULD contain the service SID. Service SID *
>
> *resolvability SHOULD NOT be checked on the ingress for this case*.”
>
>
>
>
>
> Rgds
>
> Shraddha
>
>
>
>
>
> Juniper Business Use Only
>
> *From:* Robert Raszuk <robert@raszuk.net>
> *Sent:* Tuesday, July 20, 2021 12:04 PM
> *To:* Shraddha Hegde <shraddha@juniper.net>
> *Cc:* spring@ietf.org; bess@ietf.org
> *Subject:* Re: SRv6 BGP based Overlay Services
> (draft-ietf-bess-srv6-services-07)
>
>
>
> *[External Email. Be cautious of content]*
>
>
>
> Shraddha,
>
>
>
> > that authors don’t intend to support any form of tunnelling for SRv6
>
> > because it is not optimal. Is that the right read?
>
>
>
> Quite the opposite. It is the local operator's choice (not the draft
> authors) to decide to fall back to best effort or to drop.
>
>
>
> Thx,
>
> R.
>
>
>
>
>
>
>
> On Tue, Jul 20, 2021 at 8:15 AM Shraddha Hegde <shraddha@juniper.net>
> wrote:
>
> Robert,
>
>
>
> What do you mean by SR? is it SR-MPLS or SRv6.
>
> My question is about draft-ietf-bess-srv6-services and applies only to
> SRv6.
>
>
>
> Let me repeat the question.
>
> Do the authors intend to support the case of fallback from SRv6 flex-algo
> to SRv6 best effort transport for SRv6
>
> Services or not?
>
>
>
> From your vague answer it appears that authors don’t intend to support any
> form of tunnelling for SRv6
>
> because it is not optimal. Is that the right read?
>
>
>
> Rgds
>
> Shraddha
>
>
>
>
>
> Juniper Business Use Only
>
> *From:* Robert Raszuk <robert@raszuk.net>
> *Sent:* Tuesday, July 20, 2021 11:17 AM
> *To:* Shraddha Hegde <shraddha@juniper.net>
> *Cc:* Aissaoui, Mustapha (Nokia - CA/Ottawa) <mustapha.aissaoui@nokia.com>om>;
> Rabadan, Jorge (Nokia - US/Mountain View) <jorge.rabadan@nokia.com>om>;
> Rajesh M <mrajesh@juniper.net>et>; Rajesh M <mrajesh=
> 40juniper.net@dmarc.ietf.org>gt;; Ketan Talaulikar (ketant) <ketant@cisco.com>om>;
> gdawra.ietf@gmail.com; Clarence Filsfils (cfilsfil) <cfilsfil@cisco.com>om>;
> bruno.decraene@orange.com; spring@ietf.org; bgp@ans.net; Srihari Sangli <
> ssangli@juniper.net>gt;; bess@ietf.org
> *Subject:* Re: SRv6 BGP based Overlay Services
> (draft-ietf-bess-srv6-services-07)
>
>
>
> *[External Email. Be cautious of content]*
>
>
>
> Shraddha,
>
>
>
> In an SR network fallback to best effort will also result in encapsulated
> forwarding using SR. It may not be as optimal service wise as using
> flex-algo, but this is form of tunneling. Hence I don't think your comment
> applies.
>
>
>
> Note that operator may also choose to use IP tunneling for best effort
> forwarding if SR best effort forwarding is not supported or enabled.
>
>
>
> Best,
>
> R.
>
>
>
>
>
>
>
>
>
> On Tue, Jul 20, 2021 at 7:20 AM Shraddha Hegde <shraddha@juniper.net>
> wrote:
>
> Hi Authors,
>
>
>
> There is a possibility of a usecase that wants to use flex-algo paths if
> available and if flex-algo paths
>
> Are not available use best effort paths.
>
>
>
> “When providing best-effort connectivity to the egress PE, the ingress
>
>    PE encapsulates the payload in an outer IPv6 header where the
>
>    destination address is the SRv6 Service SID associated with the
>
>    related BGP route update.  Therefore, the ingress PE SHOULD perform
>
>    resolvability check for the SRv6 Service SID before considering the
>
>    received prefix for the BGP best path computation.
>
> “
>
>
>
> The current text says for best effort tunnels Srv6 service SID resolution
> SHOULD be checked and
>
> I am told that (from previous mailing list exchanges) authors intend to
> update the text to make it applicable for flex-algo connectivity  as well.
>
>
>
> It is not possible to support fallback on best effort tunnels if flex-algo
> SRv6 service SIDs have to be resolved.
>
> It is possible to support fallback to best effort in SRv6 if packets can
> be tunneled to egress PE  (destination address being PE’s best effort END
> SID and service SID in the SRH)and
>
> then do a service SID lookup on egress, in which case there is no need to
> resolve the SRv6 service SIDs on the ingress.
>
>
>
> It is not clear whether the authors intend to support these kind of
> tunnelling to egress cases for
>
> Best effort and flex-algo transport. If it not going to be supported, pls
> add text indicating clearly
>
> Tunnelling is not required to be supported and hence Fallback to best
> effort  is also not supported.
>
>
>
> If that is not the intention, Its reasonable to update the text to
> indicate SRv6 service SIDs need not be resolved
>
> If the ingress is tunneling the packet.
>
>
>
> Rgds
>
> Shraddha
>
>
>
> Juniper Business Use Only
>
> *From:* spring <spring-bounces@ietf.org> *On Behalf Of *Aissaoui,
> Mustapha (Nokia - CA/Ottawa)
> *Sent:* Monday, July 19, 2021 7:34 PM
> *To:* Rabadan, Jorge (Nokia - US/Mountain View) <jorge.rabadan@nokia.com>om>;
> Rajesh M <mrajesh@juniper.net>et>; Rajesh M <mrajesh=
> 40juniper.net@dmarc.ietf.org>gt;; Ketan Talaulikar (ketant) <ketant@cisco.com>om>;
> gdawra.ietf@gmail.com; Clarence Filsfils (cfilsfil) <cfilsfil@cisco.com>om>;
> robert@raszuk.net; bruno.decraene@orange.com
> *Cc:* spring@ietf.org; bgp@ans.net; Srihari Sangli <ssangli@juniper.net>et>;
> bess@ietf.org; Shraddha Hegde <shraddha@juniper.net>
> *Subject:* Re: [spring] SRv6 BGP based Overlay Services
> (draft-ietf-bess-srv6-services-07)
>
>
>
> *[External Email. Be cautious of content]*
>
>
>
> Rajesh,
>
> Also you can change the service SID for a subset of prefixes using a
> policy, to apply a flex-algo for example, but you do not want to change the
> next-hop for each new service SID.
>
>
>
> Mustapha.
>
>
>
> *From:* spring <spring-bounces@ietf.org> *On Behalf Of *Rabadan, Jorge
> (Nokia - US/Mountain View)
> *Sent:* Monday, July 19, 2021 9:47 AM
> *To:* Rajesh M <mrajesh@juniper.net>et>; Rajesh M <
> mrajesh=40juniper.net@dmarc.ietf.org>gt;; Ketan Talaulikar (ketant) <
> ketant@cisco.com>gt;; gdawra.ietf@gmail.com; Clarence Filsfils (cfilsfil) <
> cfilsfil@cisco.com>gt;; robert@raszuk.net; bruno.decraene@orange.com
> *Cc:* spring@ietf.org; bgp@ans.net; Srihari Sangli <ssangli@juniper.net>et>;
> Shraddha Hegde <shraddha@juniper.net>et>; bess@ietf.org
> *Subject:* Re: [spring] SRv6 BGP based Overlay Services
> (draft-ietf-bess-srv6-services-07)
>
>
>
> Hi Rajesh,
>
>
>
> The draft is written so that the next-hop address MAY be covered by the
> locator, but there are cases in which the next-hop address is not part of
> the locator prefix, and there are implementations already allowing that, so
> I don’t agree the document should mandate what you are suggesting.
>
>
>
> Thanks.
>
> Jorge
>
>
>
> *From: *Rajesh M <mrajesh@juniper.net>
> *Date: *Monday, July 19, 2021 at 3:24 PM
> *To: *Rajesh M <mrajesh=40juniper.net@dmarc.ietf.org>rg>, Ketan Talaulikar
> (ketant) <ketant@cisco.com>om>, gdawra.ietf@gmail.com <gdawra.ietf@gmail.com>om>,
> Clarence Filsfils (cfilsfil) <cfilsfil@cisco.com>om>, robert@raszuk.net <
> robert@raszuk.net>gt;, bruno.decraene@orange.com <bruno.decraene@orange.com>om>,
> Rabadan, Jorge (Nokia - US/Mountain View) <jorge.rabadan@nokia.com>
> *Cc: *spring@ietf.org <spring@ietf.org>rg>, bgp@ans.net <bgp@ans.net>et>,
> Shraddha Hegde <shraddha@juniper.net>et>, bess@ietf.org <bess@ietf.org>rg>,
> Srihari Sangli <ssangli@juniper.net>
> *Subject: *RE: SRv6 BGP based Overlay Services
> (draft-ietf-bess-srv6-services-07)
>
> Hi Authors,
>
>
>
> Please respond.
>
>
>
> Thanks
>
> Rajesh
>
>
>
>
>
> Juniper Business Use Only
>
> *From:* spring <spring-bounces@ietf.org> *On Behalf Of *Rajesh M
> *Sent:* Thursday, July 15, 2021 4:36 PM
> *To:* Ketan Talaulikar (ketant) <ketant@cisco.com>om>; gdawra.ietf@gmail.com;
> Clarence Filsfils (cfilsfil) <cfilsfil@cisco.com>om>; robert@raszuk.net;
> bruno.decraene@orange.com; jorge.rabadan@nokia.com
> *Cc:* spring@ietf.org; bgp@ans.net; Shraddha Hegde <shraddha@juniper.net>et>;
> bess@ietf.org
> *Subject:* [spring] SRv6 BGP based Overlay Services
> (draft-ietf-bess-srv6-services-07)
>
>
>
> *[External Email. Be cautious of content]*
>
>
>
> Hi All,
>
>
>
> As per this draft, this is how resolution must work.
>
>
>
> 1)For Non Intent service Route:
>
> if BGP next hop is not reachable return.
>
> Resolve SRv6 Service SID for forwarding.
>
>
>
> 2)For Intent service Route (IGP Flex-Algo first then BGP CAR then SR
> Policy):
>
> BGP next hop is not reachable return.
>
> Resolve SRv6 Service SID for forwarding(To find IGP flex algo).if
> successfully resolves then return.
>
> Resolve BGP next hop for forwarding (in case above is not success).
>
>
>
>
>
> *Using Service SID (overlay),for resolution is definitely not recommended.*
>
>
>
> *Instead in case of srv6, we always resolve on BGP nexthop. This will be
> in line with BGP legacy.*
>
> *In case of best effort/flex algo we must mandate user to set
> corresponding locator as BGP nexthop for srv6 routes.*
>
> *I think this is a reasonable mandate.*
>
>
>
> Thanks
>
> Rajesh
>
>
>
> Juniper Business Use Only
>
>