Re: [Isis-wg] draft-hegde-isis-advertising-te-protocols-02 and draft-ginsberg-isis-te-app-00

Peter Psenak <ppsenak@cisco.com> Mon, 29 May 2017 08:15 UTC

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Date: Mon, 29 May 2017 10:15:04 +0200
From: Peter Psenak <ppsenak@cisco.com>
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To: stephane.litkowski@orange.com, "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>, Chris Bowers <cbowers@juniper.net>, "isis-wg@ietf.org" <isis-wg@ietf.org>
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Subject: Re: [Isis-wg] draft-hegde-isis-advertising-te-protocols-02 and draft-ginsberg-isis-te-app-00
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Hi Stephane,

On 29/05/17 09:45 , stephane.litkowski@orange.com wrote:
> Hi Les,
>
> I think the best approach is to have a “merged” draft rather than
> progressing your proposals as they are today.
>
> Chris’ proposal of having an opaque identifier is definitely aligned
> with my view of not having the IGP to deal with applications, it just
> carries attributes but does not need to take care on how they must be used.
>
> Even in your proposal, if you have different attributes per application,
> you will have to configure the attribute values for each application
> (case of no value sharing) on each required router or link.
>
> The only difference is the additional configuration of the mapping
> between the app and the attributes. But it’s not really a big deal, for
> TE apps, only the head end needs the mapping conf. For LFA/rLFA, it’s
> more a global config, that could be easily automated as part of router
> configuration templates (this config is not expected to move over time).
> Yes, as usual there could be some misconfiguration, but this will only
> affect the local node, not the entire network (based on the existing
> applications).
>
> I think also that the TE protocol subTLV is useful to ensure that we
> will not compute a path that uses a link that does not enable the right
> signaling protocol (similar goal as IGP/LDP sync). So the semantic is
> different as the one you proposed. Your semantic is a mapping of an
> application to a set of attributes while the TE protocol subTLV
> describes which application currently runs on a particular link (this is
> a descriptive attribute).

can you please describe me how would you use the information about an 
application running on the remote link. For example, what will you do 
with the information that LFA or SR is enabled on some remote link? What 
is the exact use case?

thanks,
Peter

>
> Brgds,
>
> Stephane
>
> *From:*Isis-wg [mailto:isis-wg-bounces@ietf.org] *On Behalf Of *Les
> Ginsberg (ginsberg)
> *Sent:* Tuesday, May 16, 2017 01:52
> *To:* Chris Bowers; isis-wg@ietf.org
> *Subject:* Re: [Isis-wg] draft-hegde-isis-advertising-te-protocols-02
> and draft-ginsberg-isis-te-app-00
>
> Chris -
>
> Thanx for the detailed write up regarding your proposed encoding for
>
> advertising link attribute information for multiple applications.
>
> My primary takeaway is that we are now in agreement regarding the need
>
> to support application specific advertisement of link attribute information.
>
> This is the major difference between the proposals in
>
> draft-ginsberg-isis-te-app/ppsenak-ospf-te-link-attr-reuse
>
> vs
>
> hegde-isis-advertising-te-protocols/hegde-ospf-advertising-te-protocols
>
> This means we have resolved the stalemate and that the respective WGs
> should
>
> now be able to begin work on the proposals based on the ginsberg/ppsenak
> drafts.
>
> This is a major step forward and I think achieves the task you and I were
>
> assigned in Chicago WG meetings.
>
> The remainder of my comments are specific to your encoding proposals -
>
> but it is worth emphasizing that we are no longer debating the
> requirements -
>
> we are simply discussing alternative encodings.
>
> Regarding Attribute Set Identifier
>
> ----------------------------------
>
> Your proposal is to define dynamically - via configuration on every
> router - a numeric
>
> identifier which represents a set of applications. Each identifier is
>
> associated with one or more applications - and that identifier is then
>
> advertised with a set of link specific attribute sub-sub-TLVs.
>
> As this is based on configuration, for correct operation the operator MUST
>
> configure consistent numeric value/application set mappings on EVERY router.
>
> To cover all possible combinations the operator would have to configure
>
> up to (2**N)-1 identifiers where N is the number of applications supported.
>
> 3 applications: up to 7 identifiers
>
> 4 applications: up to 15 identifiers
>
> 5 applications: up to 31 identifiers
>
> And the correct identifier(s) have to be associated with the appropriate
> sets of attributes
>
> on every link on each router.
>
> This seems both onerous and error prone.
>
> The stated benefit of this vs the IANA assigned bit mappings proposed
>
> by the ginsberg/ppsenak drafts is that a new application could be introduced
>
> without requiring a bit assignment by IANA. If we look at the existing
>
> applications (RSVP-TE, SR-TE, LFA) we note that all of these applications
>
> required IETF drafts be written to define interoperable behavior. I would
>
> expect the same would be required of any new application. Given that a
>
> draft is required, the inclusion of an IANA request for an application bit
>
> identifier in such a draft is trivial. By doing so we avoid the
> additional configuration
>
> and its risks of inconsistency.
>
> If the intent is to allow introduction of a proprietary or experimental
>
> application in a network prior to developing any standards I think there
>
> is a much easier way to support that. draft-ginsberg-isis-te-app currently
>
> defines:
>
>          Bit Mask Length: Non-zero (1 octet)
>
>          Application Bit Mask: Size is (Bit Mask Length+7)/8
>
>          The following bits are assigned:
>
>               0 1 2 3 4 5 6 7
>
>              +-+-+-+-+-+-+-+-+
>
>              |L|R|S|F|       |
>
>              +-+-+-+-+-+-+-+-+
>
>         L-bit: Applications listed MUST use the legacy
>
>            advertisements for the corresponding link
>
>            found in TLVs 22, 23, 141, 222, and 223 or
>
>            TLV 138 or TLV 139 as appropriate.
>
>         R-bit: RSVP-TE
>
>         S-bit: Segment Routing Traffic Engineering
>
>         F-bit: Loop Free Alternate
>
> We could reserve some bits (I think two would be enough) for non-standards
>
> use. For example
>
>               0 1 2 3 4 5 6 7
>
>              +-+-+-+-+-+-+-+-+
>
>              |L|R|S|F|   |P|X|
>
>              +-+-+-+-+-+-+-+-+
>
>         P-Bit: Reserved for proprietary application
>
>         X-bit: Reserved for experimental (pre-standard)
>
>                 application
>
> Regarding your proposal for: Traffic-engineering Protocol sub-TLV
>
> -------------------------------------------------------------------
>
> I think what you are trying to address here are the backwards compatibility
>
> concerns. Today, because we lack the ability to advertise application
> specific
>
> attributes, implementations have been forced to overload the use of the
> legacy
>
> advertisements even though such advertisements were never intended to be
> used in this way.
>
> One of the issues which the ginsberg/ppsenak drafts are addressing is
> the inappropriate use
>
> of legacy advertisements. While we do recognize that until we have full
> deployment of the
>
> extensions we need to support backwards compatibility with the existing
> overloaded use
>
> of legacy advertisements, we do NOT want to standardize this behavior.
>
> draft-ginsberg-isis-te-app provides backwards compatibility by using the
> L-bit
>
> as described above. With partial deployment we then (using the example
> of SR-TE)
>
> advertise an application bit mask with L and S bits set. This indicates that
>
> SR-TE application is using the legacy advertisements. Even after full
> deployment
>
> of the extensions this can be used to avoid unnecessary duplication when
> SR-TE
>
> and RSVP-TE share the same attributes on a given link.
>
> However, because you are proposing to use a numeric identifier, you have
> no way to
>
> indicate when SR-TE (for example) should use legacy advertisements. In
> order to do so you have
>
> to introduce another sub-TLV which uses the equivalent of the bit mask
> which the
>
> ginsberg/ppsenak drafts already utilize. And, since IANA allocations for
> the bits in this
>
> sub-TLV are still required, you have not actually eliminated the need
> for IANA bit allocations –
>
> which is one of the goals of your proposed dynamically assigned identifiers.
>
> For the proposals defined in the ginsberg/ppsenak drafts this
> information has already
>
> been conveyed via the bit mask advertised as part of the link attribute
> advertisements –
>
> so there is no need for this additional advertisement.
>
> Also note that the concept of “application enabled on a link” is not
> what is required.
>
> What is required is to identify what sets of applications can use a set
> of link attribute
>
> advertisements - which is completely captured by the new application
> specific link
>
> attribute advertisements defined in the ginsberg/ppsenak drafts.
>
> There is no need for this additional sub-TLV.
>
>     Les
>
> *From:*Isis-wg [mailto:isis-wg-bounces@ietf.org] *On Behalf Of *Chris Bowers
> *Sent:* Friday, May 12, 2017 10:47 AM
> *To:* isis-wg@ietf.org <mailto:isis-wg@ietf.org>
> *Subject:* [Isis-wg] draft-hegde-isis-advertising-te-protocols-02 and
> draft-ginsberg-isis-te-app-00
>
> ISIS-WG,
>
> As I said at the microphone at the WG meeting in Chicago, I think there
>
> may be some common ground that can address the general goals of both
>
> draft-hegde-isis-advertising-te-protocols-02 and
>
> draft-ginsberg-isis-te-app-00.
>
> The text below describes proposed encodings that I think reflect
>
> potential common ground. The main idea is to decouple the advertisement
>
> of what protocols are enabled on a link and the advertisement of
>
> different sets of attributes on a link, and then allow applications to
>
> choose how to use that information as they see fit. This takes into
>
> account input from networks operators regarding the desire for a
>
> flexible mapping between attribute sets and the applications that use
>
> them.
>
> I look forward to feedback from the WG on these proposed encodings.
>
> The text below borrows liberally from the existing text in
>
> draft-hegde-isis-advertising-te-protocols-02 and
>
> draft-ginsberg-isis-te-app-00 with some important differences.
>
> Chris
>
> ======
>
> Attribute Set Identifier
>
> The new Attribute Set Identifier is a 32-bit value that identifies a set
>
> of attributes.  All of the attributes advertised with a given value of
>
> the Attribute Set Identifier are considered to be part of the attribute
>
> set.  This allows different applications to use different attribute sets,
>
> if desired.
>
> The Attribute Set Identifier with a value of zero is special.  Existing
>
> encodings for advertising attributes that do not explicitly support the
>
> inclusion of the Attribute Set Identifier are now understood to implicitly
>
> advertise attributes with the Attribute Set Identifier set to zero.
>
> In this framework, existing implementations using the existing encodings
>
> already support the advertisement of attributes with the Attribute Set
>
> Identifier = 0.
>
> In order to ensure a consistent view of the attribute set scoped attributes,
>
> for encodings that explicitly support the Attribute Set Identifier,
>
> advertising an attribute with Attribute Set Identifier set to
>
> zero is not allowed.
>
>  From a standardization perspective, there is not intended to be any
>
> fixed mapping between a given Attribute Set Identifier and a given
>
> application. A network operator wishing to advertise different attribute
>
> sets could configure the network equipment to advertise attributes with
>
> different values of the Attribute Set Identifier based on their
>
> objectives. The different applications (be they controller-based
>
> applications or distributed applications) would make use of the
>
> different attribute sets based on convention within that network.
>
> As an example, a network operator might choose to advertise
>
> four different attribute sets, in support of five different applications
>
> with the following mapping.
>
> Application                                           Attribute Set
> Identifier
>
> ===========================              ========================
>
> Distributed RSVP-based                           0 (implicit)
>
> auto-bandwidth
>
> Centralized SR-based TE                          0 (implicit)
>
> Distributed SR-based FRR                         100
>
> Centralized RSVP-based                           200
>
> diverse low-latency paths
>
> Potential new application                        300
>
> that uses both SR and RSVP
>
> to build LSPs
>
> Below are descriptions of proposed encodings that allow attributes to
>
> be advertised with non-zero values of the Attribute Set Identifier.
>
> The Traffic-engineering Protocol sub-TLV is described as well, since it is
>
> needed to indicate what protocols are enabled on a link.
>
> ======
>
> Link Attribute Set sub-TLV
>
> The Link Attribute Set sub-TLV is a new sub-TLV for TLVs 22, 23, 141,
>
> 222, and 223. It allows different sets of link attributes to be
>
> advertised for the same link. This allows different applications to use
>
> different sets of attributes.
>
>          Type: to be assigned by IANA (suggested value 101 )
>
>          Length: Variable (1 octet)
>
>          Value:
>
>                  Attribute Set Identifier - a 32-bit value containing
> the non-zero
>
>                  Attribute Set Identifier that identifies a set of
> attributes. The Link
>
>                  Attribute Set sub-TLV MUST be ignored if the Attribute
> Set Identifier is
>
>                  zero. This ensures a consistent view of the attribute
> set scoped link
>
>                  attributes, where the Link Attribute sub-TLVs
> advertised directly
>
>                  in TLV#22 are now understood to be implicitly
> advertised with the
>
>                  Attribute Set Identifier equal to zero.
>
>                  Link Attribute sub-sub-TLVs - the format of these Link
> Attribute
>
>                  sub-sub-TLVs matches the existing formats for the Link
> Attribute
>
>                  sub-TLVs defined in [RFC5305] and [RFC7810]. Each Link
> Attribute
>
>                  sub-sub-TLV advertised in a given Link Attribute Set
> sub-TLV is
>
>                  associated with the Attribute Set Identifier in the
> Link Attribute Set
>
>                  sub-TLV.
>
> =======
>
> Attribute Set Scoped SRLG TLV
>
> A new TLV is defined to allow SRLGs to be advertised for a
>
> given link and associated with a specific attribute set identifier.
>
> Although similar in functionality to TLV 138 (defined by
>
> [RFC5307]) and TLV 139 (defined by [RFC6119] a single TLV provides
>
> support for IPv4, IPv6, and unnumbered identifiers for a link.
>
> Unlike TLVs 138/139 it utilizes sub-TLVs to encode the link
>
> identifiers in order to provide the flexible formatting required to
>
> support multiple link identifier types.
>
>          Type: to be assigned by IANA (suggested value 238)
>
>          Length: Number of octets in the value field (1 octet)
>
>          Value:
>
>                  Neighbor System-ID + pseudo-node ID (7 octets)
>
>                  Attribute Set Identifier - a 32-bit value containing
> the non-zero
>
>                  Attribute Set Identifier that identifies a set of
> attributes. The
>
>                  Attribute Set Scoped SRLG TLV MUST be ignored if the
> Attribute Set Identifier is
>
>                  zero. This ensures a consistent view of the attribute
> set scoped link
>
>                  attributes, where the SRLGs advertised directly in
> TLV#138 and TLV#139
>
>                  are now understood to be implicitly advertised with the
>
>                  Attribute Set Identifier equal to zero.
>
>                  Length of sub-TLVs (1 octet)
>
>                  Link Identifier sub-TLVs (variable)
>
>                  0 or more SRLG Values (Each value is 4 octets)
>
>          The following Link Identifier sub-TLVs are defined. The type
>
>          values are suggested and will be assigned by IANA - but as
>
>          the formats are identical to existing sub-TLVs defined for
>
>          TLVs 22, 23, 141, 222, and 223 the use of the suggested sub-TLV
>
>          types is strongly encouraged.
>
>                     Type    Description
>
>                          4      Link Local/Remote Identifiers (see
> [RFC5307])
>
>                          6      IPv4 interface address (see [RFC5305])
>
>                          8      IPv4 neighbor address (see [RFC5305])
>
>                     12      IPv6 Interface Address (see [RFC6119])
>
>                     13      IPv6 Neighbor Address (see [RFC6119])
>
>     At least one set of link identifiers (IPv4, IPv6, or unnumbered) MUST
>
>     be present.  TLVs which do not meet this requirement MUST be ignored.
>
>     Multiple TLVs for the same link MAY be advertised.
>
> =======
>
> Traffic-engineering Protocol sub-TLV
>
> A new Traffic-engineering protocol sub-TLV is a new sub-TLV for TLVs 22,
>
> 23, 141, 222, and 223. The sub-TLV indicates the protocols enabled on
>
> the link. The sub-TLV has flags in the value field to indicate the
>
> protocol enabled on the link. The length field is variable to allow the
>
> flags field to grow for future requirements.
>
>      Type  : to be assigned by IANA (suggested value 102)
>
>      Length: Variable (1 octet)
>
>      Value:
>
>             The value field consists of bits indicating the protocols
>
>             enabled on the link.  This document defines the two protocol
> values
>
>             below.
>
>        0                   1                   2                   3
>
>        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>       |                         Flags                                 |
>
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>                 +----------+-------------------------------+
>
>                 | Value    | Protocol Name                 |
>
>                 +----------+-------------------------------+
>
>                 |0x01      | RSVP                          |
>
>                 +----------+-------------------------------+
>
>                 |0x02      | Segment Routing               |
>
>                 +----------+-------------------------------+
>
>          The RSVP flag is set to one to indicate that RSVP-TE is enabled
> on a
>
>          link.  The RSVP flag is set to zero to indicate that RSVP-TE is not
>
>          enabled on a link.
>
>          The Segment Routing flag is set to one to indicate that Segment
>
>          Routing is enabled on a link.  The Segment Routing flag is set to
>
>          zero to indicate that Segment Routing is not enabled on a link
>
> ========
>
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