Re: [spring] draft-ginsberg-spring-conflict-resolution - WG adoption call

[<[e-mail]>]

Hi Les,

Please see inline.


> From: Les Ginsberg (ginsberg) [mailto:[e-mail]] > Sent: Saturday, May 14, 2016 7:04 PM
> 
> Uma -
> 
> I'd like to close this point of discussion as regards the conflict-resolution draft.
> 
> For the record, I agree with Peter. But from the standpoint of conflict
> resolution it matters not for what purpose SRMS is being used

In order for all nodes to consider the same SR data during the SR-conflict algo, what matters is whether all node within a domain MUST support SRMS or not,.
So 2 options:
- SRMS is mandatary to implement or to deploy consistently, and this need to be stated somewhere, e.g. in spring-conflict-resolution. (e.g. in the early days, this was not the case for all implementations)
- the SR-conflict algo is defined in a way to give the same result, for a Prefix-SID, with partial SRMS deployment. This may be feasible is SID-Prefix info are given strict priority over SRMS.

Thanks,
--Bruno

> - we have to
> consider SRMS advertisements as well as SIDs associated w prefix
> advertisements. I hope that point has been clearly explained.
> 
> If you wish to continue the discussion with the architecture draft authors as
> to whether further discussion of SRMS as a network provisioning tool
> should/should not be added to a document please feel free to do so - but I
> would ask that you do so in another thread.
> Thanx.
> 
>    Les
> 
> 
> > -----Original Message-----
> > From: Peter Psenak (ppsenak)
> > Sent: Friday, May 13, 2016 12:31 AM
> > To: Uma Chunduri; Stefano Previdi (sprevidi)
> > Cc: Les Ginsberg (ginsberg); [e-mail]; [e-mail]
> > Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
> adoption
> > call
> >
> > Uma,
> >
> > I don't know whether you need a text in the draft/RFC to use some
> > functionality one way or the other. The fact is that SRMS is a SID
> provisioning
> > tool. You can use it for SR/LDP interoperability, but you can also use it in a
> SR
> > only network to provide SIDs from a central place instead of configuring
> them
> > on each device. There is nothing that prevents you to use it one way or the
> > other. The fact that SRMS is defined in the SR/LDP interop drfat does not
> > mean it is restricted to be used for that purpose.
> >
> > I let authors of the SR architecture drafts to decide whether they want to
> add
> > the text. As an author of the OSPF SR draft, I do not see anything in the
> text
> > that you put below that would contradict what I'm saying here.
> >
> > thanks,
> > Peter
> >
> >
> > On 5/12/16 20:19 , Uma Chunduri wrote:
> > > Peter,
> > >          > as a matter of fact, SRMS is a SID provisioning tool,
> > > whether you like it or not.
> > > It's not about your or my linking - I was talking about what's the
> > > defined scope so far (architecture doc or protocol docs) and how you
> > > want to extend the scope.
> > > Well, if you want to extend the current scope of SRMS as a "">2)As a
> > > global provisioning tool" - Plz. do so but not while providing
> > > conflict resolution solution.
> > >                 > It provides all the functionality that is required
> > > for such provisioning tool.
> > >          >You can not restrict its usage to SR/LDP interop case.
> > > I didn't restrict anything - Plz. see SRMS stuff so far:
> > > 1.
> > > _https://tools.ietf.org/html/draft-ietf-spring-segment-routing-08#sect
> > > ion-3.6_
> > >
> > > /" //3.6.1.  Mapping Server/
> > > ///A Remote-Binding SID S advertised by the mapping server M for
> > > remote/ ///prefix R attached to non-SR-capable node N signals the
> > > same/ ///information as if N had advertised S as a Prefix-SID.
> > > Further/ ///details are described in the SR/LDP interworking
> > > procedures/ ///([I-D.ietf-spring-segment-routing-ldp-interop].//"/
> > > 2. ISIS:
> > > _https://tools.ietf.org/html/draft-ietf-isis-segment-routing-extension
> > > s-06#section-2.4_
> > >
> > > /" //This functionality is called the/ /////'Mapping Server' and it's
> > > used when, in a heterogeneous network,/ ///////not all nodes are
> > > capable of advertising their own SIDs/Labels.//"/ 3. OSPF:
> > > _https://tools.ietf.org/html/draft-ietf-ospf-segment-routing-extension
> > > s-08#section-4_
> > >
> > > /"//   In some cases it is useful to advertise attributes for a range of/
> > > ///prefixes.  The Segment Routing Mapping Server, which is described
> > > in/ ///[//I-D.filsfils-spring-segment-routing-ldp-interop/
> > > <https://tools.ietf.org/html/draft-ietf-ospf-segment-routing-extension
> > > s-08>/],
> > > is an example/
> > > ///where we need a single advertisement to advertise SIDs for
> > > multiple/ ///prefixes from a contiguous address range.//"/ Again, plz.
> > > extend the scope first and consider the same in resolution solution. I
> > > am fine with it.
> > > --
> > > Uma C.
> > > -----Original Message-----
> > > From: Peter Psenak [mailto:[e-mail]]
> > > Sent: Thursday, May 12, 2016 11:03 AM
> > > To: Uma Chunduri; Stefano Previdi (sprevidi)
> > > Cc: Les Ginsberg (ginsberg); [e-mail];
> > > [e-mail]
> > > Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
> > > adoption call Hi Uma, On 5/12/16 19:49 , Uma Chunduri wrote:
> > >> Stefano,
> > >>
> > >> Thanks for your response.
> > >>
> > >>        > using a SRMS for advertising SID on behalf of SR capable nodes
> does
> > not introduce any change in the SR architecture so not
> > >>                 > sure what we need to document here.
> > >>
> > >> My point below: We are creating a conflict resolution solution for a non-
> > existing requirement of using  SRMS viz.,  ">2)As a global provisioning tool".
> > >>  From your statement above, it seems you have less interest to make
> this
> > as a requirement/scope of SRMS; I am more aligned in that path....
> > > as a matter of fact, SRMS is a SID provisioning tool, whether you like
> > > it or not. It provides all the functionality that is required for such
> > > provisioning tool. You can not restrict its usage to SR/LDP interop case.
> > > thanks,
> > > Peter
> > >>
> > >> On the second point:
> > >>
> > >>        > the architecture draft is data-pane agnostic so I presume you refer
> > to draft-ietf-spring-segment-routing-mpls.
> > >>
> > >> AFAIS,https://tools.ietf.org/html/draft-ietf-spring-segment-routing-0
> > >> 8  talks
> > > about both data planes right from abstract to multiple places (which
> > > it ought to).
> > >> I leave this to you/WG on where you want to document this -but IMO
> > >> conflict resolution "solution document" in the current form potentially
> > introducing fundamental requirements  to the system like cross protocol
> > verification (with in/across AS). Perhaps some discussion should be there in
> > data plane document then.
> > >>
> > >> --
> > >> Uma C.
> > >>
> > >>
> > >> -----Original Message-----
> > >> From: Stefano Previdi (sprevidi) [mailto:[e-mail]]
> > >> Sent: Wednesday, May 11, 2016 4:46 AM
> > >> To: Uma Chunduri
> > >> Cc: Les Ginsberg (ginsberg);[e-mail]
> > >><mailto:[e-mail]>;
> > >>[e-mail] <mailto:[e-mail]>
> > >> Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
> > >>adoption call
> > >>
> > >>
> > >>> On May 6, 2016, at 10:16 PM, Uma Chunduri
> > <[e-mail] <mailto:[e-mail]>>
> > wrote:
> > >>>
> > >>> Les,
> > >>>
> > >>> 2 quick things.
> > >>>
> > >>> 1.
> > >>>              >[Les:] There are two legitimate use cases for SRMS:
> > >>>                                             >1)To advertise SIDs for non-SR capable nodes
> > >>>                                             >2)As a global provisioning tool
> > >>>                           I am hearing #2 for the first time. I
> > >>>don’t see this either  discussed earlier in the WG list  or captured
> > >>>in architecture document
> > >>>https://tools.ietf.org/html/draft-ietf-spring-segment-routing-07.
> > >>>Even
> > > in the protocol extensions document for example
> > >>>https://tools.ietf.org/html/draft-ietf-isis-segment-routing-extension
> > >>>s-06#section-2.4
> > > we always discussed this from non-SR
> > >>>                           capable nodes PoV. So I request to add this in architecture
> > document before factoring this for solution in conflict resolution.
> > >>
> > >>
> > >> using a SRMS for advertising SID on behalf of SR capable nodes does not
> > introduce any change in the SR architecture so not sure what we need to
> > document here.
> > >>
> > >>
> > >>
> > >>>
> > >>> 2.       Also this is the first time ever we have a requirement for cross
> > protocols verification we ought to discuss the implications of this
> > >>> and protocols involved (with in AS or otherwise) in the architecture
> > document (at least briefly).
> > >>
> > >>
> > >> the architecture draft is data-pane agnostic so I presume you refer to
> > draft-ietf-spring-segment-routing-mpls.
> > >>
> > >> with the ipv6 data-plane SR conflicts are in fact solved by ipv6
> > >> addressing techniques ;-)
> > >>
> > >> s.
> > >>
> > >>
> > >>>
> > >>> --
> > >>> Uma C.
> > >>>
> > >>> From: spring [mailto:[e-mail]] On Behalf Of Les
> > >>> Ginsberg (ginsberg)
> > >>> Sent: Wednesday, May 04, 2016 9:38 AM
> > >>> To: Uma Chunduri;[e-mail]
> > >>> <mailto:[e-mail]>;
> > > [e-mail] <mailto:[e-mail]>
> > >>> Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
> > >>> adoption call
> > >>>
> > >>> Uma –
> > >>>
> > >>> To restate, the problem being addressed here is to guarantee
> > >>> consistent use of SIDs in the forwarding plane network-wide in the
> > >>> presence of conflicting advertisements. The set of advertisements
> > >>> includes both SIDs advertised in protocol prefix reachability
> > >>> advertisements and SRMS advertisements because problems occur
> > based
> > > upon inconsistencies in what is installed in the forwarding plane of
> > > different routers. It matters not whether Router A used a SID
> > > advertised by a protocol prefix reachability advertisement or by an
> > > SRMS advertisement – what matter is whether the SID used is consistent
> > > with what the neighbors of Router A use. So simply ensuring that OSPF
> > > (for
> > > example) resolves SIDs in a consistent way does not fully address the
> > > problem space.
> > >>>
> > >>> More inline.
> > >>>
> > >>> From: Uma Chunduri [mailto:[e-mail]]
> > >>> Sent: Tuesday, May 03, 2016 3:59 PM
> > >>> To: Les Ginsberg (ginsberg);[e-mail]
> > >>><mailto:[e-mail]>;
> > >>>[e-mail] <mailto:[e-mail]>
> > >>> Subject: RE: [spring] draft-ginsberg-spring-conflict-resolution - WG
> > >>>adoption call
> > >>>
> > >>> Les,
> > >>>
> > >>> With all due respects, cross protocol verification  of prefix and SID
> > conflicts as an “architectural change”  and it can severely impact the existing
> > implementations (at least the one I work on).
> > >>>
> > >>> [Les:] It is quite correct – and I can confirm based on personal
> > experience – that support for conflict resolution is a significant effort.
> > >>>
> > >>> Also I have couple of cases where current version of the draft is not
> clear
> > about resolution.
> > >>>
> > >>> IMO, first we need clarity with in a protocol instance resolution rules
> > before going to resolve the same across protocols (I mentioned few cases
> > below) .
> > >>> Separation of reachability advertisements and SRMS would help “cross
> > protocol” verification of the ranges and SRMS is not applicable to all
> > protocols.
> > >>>
> > >>>
> > >>> In-line [Uma]:
> > >>>
> > >>> --
> > >>> Uma C.
> > >>>
> > >>> From: Les Ginsberg (ginsberg) [mailto:[e-mail]]
> > >>> Sent: Saturday, April 30, 2016 10:11 PM
> > >>> To: Uma Chunduri;[e-mail]
> > >>> <mailto:[e-mail]>;
> > > [e-mail] <mailto:[e-mail]>
> > >>> Subject: RE: [spring] draft-ginsberg-spring-conflict-resolution - WG
> > >>> adoption call
> > >>>
> > >>> Uma –
> > >>>
> > >>> We are indeed defining conflict resolution across all the SID
> > >>> advertisements regardless of source (protocol or SRMS) –
> > >>>
> > >>> [Uma]: While you can theoretically do anything for current
> > implementation this kind of cross protocol verification is a new architectural
> > requirement.
> > >>>                 Because it seems “a central entity” need to gather all different
> > protocol instances SRMS advertisements and should settle with resolution.
> > >>>
> > >>> -          Also note SRMS is not applicable for BGP but it seems all prefix
> SIDs
> > need to be verified  with IGP instances SRMS advertisements. Is this true?
> > While the document mostly talks about these and compares with prefix
> > advertisement.
> > >>> [Les:] The issue is protocol agnostic.
> > >>>
> > >>> -          Algorithm proposed needs more clarity: Take Section 3.2.4
> > >>>
> > >>> o
> > >>>                        “   1.  Smaller range wins
> > >>>
> > >>>               2.  IPv6 entry wins over IPv4 entry
> > >>>               …
> > >>>          “
> > >>>                   What happens in case of prefix conflict or SID conflict with
> only
> > prefix advertisements (range 1).  Say multiple prefixes have same SID in
> one
> > protocol instance and in different protocols.
> > >>>                   I see 2 levels of resolution required viz., one at within the
> > protocol and one among the protocols.  No discussion on this.
> > >>>
> > >>> [Les:] The full set of rules specified in the draft provide deterministic
> > resolution in all cases. You have snipped only the first two rules. If a
> > preference is not obtained based on the first two rules you continue on to
> > rule #3, then rule #4, etc.
> > >>>
> > >>>                   Similarly in case of SID conflict  (range 1), it’s not specified
> which
> > protocol’s SID need to be considered.  Are you assuming some sort of
> Admin
> > distance play a role in resolution?
> > >>> [Les:] No – admin distance plays no role here.
> > >>>
> > >>>   I don’t see any discussion in the document  and needs more clarity
> > there too.
> > >>> o   Also what happens if a prefix or SID conflict happens with SRMS
> range
> > 1 and a prefix  advertisement (2 cases)
> > >>> a.       of one protocol and
> > >>> b.      multiple protocols?
> > >>>
> > >>> [Les:] The source of the SID advertisement (what protocol/protocol
> > instance or whether it is SRMS based) plays no role. The tie breaker rules as
> > defined are complete and provide a deterministic answer in all cases.
> > >>> If you believe that is not true please provide a specific example where
> > you apply all the rules in the order specified and still do not determine the
> > preferred entry.
> > >>>
> > >>>
> > >>> -          On the below assumption: (Section 3.2.4)
> > >>>                                           “This has the nice property that a single
> > misconfiguratoion of an SRMS
> > >>>                   entry with a large range will not be preferred over a large
> > number of
> > >>>                   SIDs advertised in prefix reachability advertisements.”
> > >>> While anything can happen in theory, I found it bit odd to see why
> SRMS
> > entry is being advertised and for the same prefix, SID is also advertised
> > through reachability advertisements?
> > >>> This is against the spirit of SRMS advertisement, isn’t it? While this can
> > happen, it seems we are claiming resolution solution by focusing more on
> > this case in the current version of the document.
> > >>>
> > >>> [Les:] There are two legitimate use cases for SRMS:
> > >>>
> > >>> 1)To advertise SIDs for non-SR capable nodes 2)As a global
> > >>> provisioning tool
> > >>>
> > >>> Let’s examine the first case. I have an LDP enabled network and I begin
> > introducing SR capable nodes. At a given moment in time Router A is NOT
> SR
> > capable and SRMS advertisements cover prefix SIDs for the addresses
> > associated with Router A.
> > >>> I then upgrade Router A to become SR capable. Because I want to do
> > >>> “make-before-break” I do not immediately remove the SRMS
> > >>> advertisements covering the addresses associated with Router A. I
> > >>> upgrade A, add configuration of SIDs locally on Router A, and
> > >>> verify that the advertisements originating from protocols on Router
> > >>> A
> > > are correct. If an inconsistency is introduced when configuring the
> > > SIDs on Router A then I will have an SRMS advertisement and a
> > > prefix-reachability advertisement that conflict. Until the conflict is
> > > corrected we use the conflict resolution rules to provide
> > > deterministic forwarding behavior.
> > >>>
> > >>> This to me is a normal and expected upgrade scenario.
> > >>>
> > >>>
> > >>> This is one of the reasons of my first comment below. You got to
> > separate the reachability advertisements and SRMS advertisements; as in
> > principle these are defined for different purposes. I don’t see we  need
> > algorithm to prefer reachability advertisement  over SRMS advertisement
> (if
> > we don’t compare these 2 categories).
> > >>>
> > >>>
> > >>>
> > >>> [Les:] I disagree – hopefully my comments have helped you to
> > understand why.
> > >>>
> > >>>     Les
> > >>>
> > >>>
> > >>> as the sections you have quoted clearly state.
> > >>>
> > >>> Why? Because we need consistent use of SIDs in the forwarding plane.
> > From forwarding perspective it matters not whether the SID was
> advertised
> > by protocol instance #1 or #2 or by an SRMS.
> > >>>
> > >>> What matters is that the SID I use to determine what label I install in
> my
> > forwarding plane is the same SID that my neighbors will use. Otherwise
> > forwarding will be broken.
> > >>>
> > >>>     Les
> > >>>
> > >>>
> > >>> From: spring [mailto:[e-mail]] On Behalf Of Uma
> > >>> Chunduri
> > >>> Sent: Wednesday, April 27, 2016 4:31 PM
> > To:[e-mail]
> > >>> <mailto:[e-mail]>;
> > > [e-mail] <mailto:[e-mail]>
> > >>> Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
> > >>> adoption call
> > >>>
> > >>> Dear Authors,
> > >>>
> > >>> Have few comments on the draft:
> > >>>
> > >>> 1.
> > >>>          As I indicated during meeting - I am not sure why we have to club
> > verification of SIDs advertised through regular protocol reachability
> > >>>                  prefixes and the ranges advertised through 'Mapping Server'
> > (SRMS). I didn't see any compelling reason to do this.
> > >>>                   SIDs advertised through reachability prefixes doesn't have
> > ranges unlike SRMS advertisements.
> > >>>                   As SRMS advertisements are primarily for nodes which are
> not
> > SR capable and  I feel we should not mix this with nodes which are SR
> > capable.
> > >>>
> > >>>          This isolation helps restricting the resolution work primarily for
> > multiple SRMS entries advertised through one node or multiple nodes.
> > >>>                  SRMS advertisements are indeed little bit unique in that you
> are
> > advertising "configuration" on behalf of node X from node Y
> > >>>                  with ranges (both prefix ranges and SID ranges).
> > >>>
> > >>>
> > >>> 2.
> > >>>                  Regarding  the scope of conflict resolution:
> > >>>
> > >>>
> > >>>         Section 1
> > >>>
> > >>>             "   The problem to be addressed is protocol independent i.e.,
> > segment
> > >>>           related advertisements may be originated by multiple nodes
> using
> > >>>           different protocols and yet the conflict resolution MUST be the
> > same
> > >>>           on all nodes regardless of the protocol used to transport the
> > >>>           advertisements."
> > >>>
> > >>>          Section 3.2.8
> > >>>            "   o  In cases where multiple routing protocols are in use mapping
> > >>>        entries advertised by all routing protocols MUST be included."
> > >>>
> > >>>        This sounds like we are seeking to resolve conflicting entries
> outside
> > and across the protocols?
> > >>>        Each IGP has separate mechanism for advertising mapping entry
> and
> > I this is not clear with the current version of the draft how we can cross
> verify
> > SID/Prefix conflict across  the protocol.
> > >>>       Can you clarify this?
> > >>>
> > >>>
> > >>> --
> > >>> Uma C.
> > >>>
> > >>>
> > >>> -----Original Message-----
> > >>> From: spring [mailto:[e-mail]] On Behalf Of
> > >>>[e-mail] <mailto:[e-mail]>
> > >>> Sent: Thursday, April 14, 2016 12:55 AM  To:[e-mail]
> > >>><mailto:[e-mail]>
> > >>> Subject: Re: [spring] draft-ginsberg-spring-conflict-resolution - WG
> > >>>adoption call
> > >>>
> > >>>> From:[e-mail]
> > <mailto:[e-mail]> > Sent:
> > > Thursday, April 14, 2016
> > >>>> 9:51 AM
> > >>>>
> > >>>> Dear WG,
> > >>>>
> > >>>> As we discussed at our meeting last week, working group adoption
> > >>>> has been requested for draft-ginsberg-spring-conflict-resolution.
> > >>>> Please reply to the list with your comments, including although not
> > >>>> limited to whether or not you support adoption.
> > >>>
> > >>> We will end the call on April 29, 2016.
> > >>>
> > >>>
> > >>>> Thanks,
> > >>>>
> > >>>> --John and Bruno
> > >>>>
> > >>>>
> > >>>>
> > >>>>
> >
> __________________________________________________________
> > >>>>
> >
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