LSR Working Group                                         P. Psenak, Ed.
Internet-Draft                                               L. Ginsberg
Intended status: Standards Track                           Cisco Systems
Expires: November 8, 2020                                  W. Henderickx
                                                                   Nokia
                                                             J. Tantsura
                                                                  Apstra
                                                                J. Drake
                                                        Juniper Networks
                                                             May 7, 2020


             OSPF Link Traffic Engineering Attribute Reuse
               draft-ietf-ospf-te-link-attr-reuse-11.txt

Abstract

   Existing traffic engineering related link attribute advertisements
   have been defined and are used in RSVP-TE deployments.  Since the
   original RSVP-TE use case was defined, additional applications (e.g.,
   Segment Routing Traffic Engineering, Loop Free Alternate) have been
   defined which also make use of the link attribute advertisements.  In
   cases where multiple applications wish to make use of these link
   attributes the current advertisements do not support application
   specific values for a given attribute nor do they support indication
   of which applications are using the advertised value for a given
   link.  This document introduces new link attribute advertisements in
   OSPFv2 and OSPFv3 which address both of these shortcomings.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 8, 2020.






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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Existing Advertisement of Link Attributes . . . . . . . . . .   4
   4.  Advertisement of Link Attributes  . . . . . . . . . . . . . .   4
     4.1.  OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA .   4
   5.  Advertisement of Application Specific Values  . . . . . . . .   5
   6.  Reused TE link attributes . . . . . . . . . . . . . . . . . .   8
     6.1.  Shared Risk Link Group (SRLG) . . . . . . . . . . . . . .   8
     6.2.  Extended Metrics  . . . . . . . . . . . . . . . . . . . .   8
     6.3.  Administrative Group  . . . . . . . . . . . . . . . . . .   9
     6.4.  Traffic Engineering Metric  . . . . . . . . . . . . . . .  10
   7.  Maximum Link Bandwidth  . . . . . . . . . . . . . . . . . . .  10
   8.  Considerations for Extended TE Metrics  . . . . . . . . . . .  10
   9.  Local Interface IPv6 Address Sub-TLV  . . . . . . . . . . . .  11
   10. Remote Interface IPv6 Address Sub-TLV . . . . . . . . . . . .  11
   11. Attribute Advertisements and Enablement . . . . . . . . . . .  11
   12. Deployment Considerations . . . . . . . . . . . . . . . . . .  12
     12.1.  Use of Legacy RSVP-TE LSA Advertisements . . . . . . . .  12
     12.2.  Use of Zero Length Application Identifier Bit Masks  . .  13
     12.3.  Interoperability, Backwards Compatibility and Migration
            Concerns . . . . . . . . . . . . . . . . . . . . . . . .  13
       12.3.1.  Multiple Applications: Common Attributes with  RSVP-
                TE . . . . . . . . . . . . . . . . . . . . . . . . .  13
       12.3.2.  Multiple Applications: Some Attributes Not Shared
                with RSVP-TE . . . . . . . . . . . . . . . . . . . .  14
       12.3.3.  Interoperability with Legacy Routers . . . . . . . .  14
       12.3.4.  Use of Application Specific Advertisements for RSVP-
                TE . . . . . . . . . . . . . . . . . . . . . . . . .  15
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  15
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     14.1.  OSPFv2 . . . . . . . . . . . . . . . . . . . . . . . . .  16



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     14.2.  OSPFv3 . . . . . . . . . . . . . . . . . . . . . . . . .  16
   15. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   17. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     17.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     17.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   Advertisement of link attributes by the OSPFv2 [RFC2328] and OSPFv3
   [RFC5340] protocols in support of traffic engineering (TE) was
   introduced by [RFC3630] and [RFC5329] respectively.  It has been
   extended by [RFC4203], [RFC7308] and [RFC7471].  Use of these
   extensions has been associated with deployments supporting Traffic
   Engineering over Multiprotocol Label Switching (MPLS) in the presence
   of the Resource Reservation Protocol (RSVP) - more succinctly
   referred to as RSVP-TE [RFC3209].

   For the purposes of this document an application is a technology
   which makes use of link attribute advertisements - examples of which
   are listed in Section 5.

   In recent years new applications have been introduced which have use
   cases for many of the link attributes historically used by RSVP-TE.
   Such applications include Segment Routing Traffic Engineering (SRTE)
   [I-D.ietf-spring-segment-routing-policy] and Loop Free Alternates
   (LFA) [RFC5286].  This has introduced ambiguity in that if a
   deployment includes a mix of RSVP-TE support and SRTE support (for
   example) it is not possible to unambiguously indicate which
   advertisements are to be used by RSVP-TE and which advertisements are
   to be used by SRTE.  If the topologies are fully congruent this may
   not be an issue, but any incongruence leads to ambiguity.

   An additional issue arises in cases where both applications are
   supported on a link but the link attribute values associated with
   each application differ.  Current advertisements do not support
   advertising application specific values for the same attribute on a
   specific link.

   This document defines extensions which address these issues.  Also,
   as evolution of use cases for link attributes can be expected to
   continue in the years to come, this document defines a solution which
   is easily extensible for the introduction of new applications and new
   use cases.






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2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Existing Advertisement of Link Attributes

   There are existing advertisements used in support of RSVP-TE.  These
   advertisements are carried in the OSPFv2 TE Opaque LSA [RFC3630] and
   OSPFv3 Intra-Area-TE-LSA [RFC5329].  Additional RSVP-TE link
   attributes have been defined by [RFC4203], [RFC7308] and [RFC7471].

   Extended Link Opaque LSAs as defined in [RFC7684] for OSPFv2 and
   Extended Router-LSAs [RFC8362] for OSPFv3 are used to advertise link
   attributes that are used by applications other then RSVP-TE or GMPLS.
   These LSAs were defined as a generic containers for distribution of
   the extended link attributes.

4.  Advertisement of Link Attributes

   This section outlines the solution for advertising link attributes
   originally defined for RSVP-TE or GMPLS when they are used for other
   applications.

4.1.  OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA

   Advantages of Extended Link Opaque LSAs as defined in [RFC7684] for
   OSPFv2 and Extended Router-LSAs [RFC8362] for OSPFv3 when used for
   advertisement of link attributes originally defined for RSVP-TE or
   GMPLS:

   1.  Advertisement of the link attributes does not make the link part
       of the RSVP-TE topology.  It avoids any conflicts and is fully
       compatible with [RFC3630] and [RFC5329].

   2.  The OSPFv2 TE Opaque LSA and OSPFv3 Intra-Area-TE-LSA remains
       truly opaque to OSPFv2 and OSPFv3 as originally defined in
       [RFC3630] and [RFC5329] respectively.  Their contents are not
       inspected by OSPF, that acts as a pure transport.

   3.  There is clear distinction between link attributes used by RSVP-
       TE and link attributes used by other OSPFv2 or OSPFv3
       applications.





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   4.  All link attributes that are used by other applications are
       advertised in a single LSA, the Extended Link Opaque LSA in
       OSPFv2 or the OSPFv3 E-Router-LSA [RFC8362] in OSPFv3.

   The disadvantage of this approach is that in rare cases, the same
   link attribute is advertised in both the TE Opaque and Extended Link
   Attribute LSAs in OSPFv2 or the Intra-Area-TE-LSA and E-Router-LSA in
   OSPFv3.

   Extended Link Opaque LSA [RFC7684] and E-Router-LSA [RFC8362] are
   used to advertise any link attributes used for non-RSVP-TE
   applications in OSPFv2 or OSPFv3 respectively, including those that
   have been originally defined for RSVP-TE applications (See
   Section 6).

   TE link attributes used for RSVP-TE/GMPLS continue use OSPFv2 TE
   Opaque LSA [RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329].

   The format of the link attribute TLVs that have been defined for
   RSVP-TE applications will be kept unchanged even when they are used
   for non-RSVP-TE applications.  Unique code points are allocated for
   these link attribute TLVs from the OSPFv2 Extended Link TLV Sub-TLV
   Registry [RFC7684] and from the OSPFv3 Extended LSA Sub-TLV Registry
   [RFC8362], as specified in Section 14.

5.  Advertisement of Application Specific Values

   To allow advertisement of the application specific values of the link
   attribute, a new Application Specific Link Attributes (ASLA) sub-TLV
   is defined.  The ASLA sub-TLV is a sub-TLV of the OSPFv2 Extended
   Link TLV [RFC7684] and OSPFv3 Router-Link TLV [RFC8362].

   The ASLA sub-TLV is an optional sub-TLV and can appear multiple times
   in the OSPFv2 Extended Link TLV and OSPFv3 Router-Link TLV.  The ASLA
   sub-TLV MUST be used for advertisement of the link attributes listed
   at the end on this section if these are advertised inside OSPFv2
   Extended Link TLV and OSPFv3 Router-Link TLV.  It has the following
   format:













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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  SABM Length  |  UDABM Length |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Standard Application Identifier Bit-Mask             |
   +-                                                             -+
   |                            ...                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           User Defined Application Identifier Bit-Mask        |
   +-                                                             -+
   |                            ...                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Link Attribute sub-sub-TLVs              |
   +-                                                             -+
   |                            ...                                |

   where:

      Type: 10 (OSPFv2), 11 (OSPFv3)

      Length: variable

      SABM Length: Standard Application Identifier Bit-Mask Length in
      octets.  The legal values are 0, 4 or 8.  If the Standard
      Application Bit-Mask is not present, the Standard Application Bit-
      Mask Length MUST be set to 0.

      UDABM Length: User Defined Application Identifier Bit-Mask Length
      in octets.  The legal values are 0, 4 or 8.  If the User Defined
      Application Bit-Mask is not present, the User Defined Application
      Bit-Mask Length MUST be set to 0.

      Standard Application Identifier Bit-Mask: Optional set of bits,
      where each bit represents a single standard application.  Bits are
      defined in [I-D.ietf-isis-te-app].  The bits are repeated here for
      informational purpose:

         Bit-0 (R-bit): RSVP-TE

         Bit-1 (S-bit): Segment Routing TE

         Bit-2 (F-bit): Loop Free Alternate (LFA).  Includes all LFA
         types





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      User Defined Application Identifier Bit-Mask: Optional set of
      bits, where each bit represents a single user defined application.

   If the SABM or UDABM length is other than 0, 4, or 8, the ASLA sub-
   TLV MUST be ignored by the receiver.

   Standard Application Identifier Bits are defined/sent starting with
   Bit 0.  Undefined bits MUST be transmitted as 0 and MUST be ignored
   on receipt.  Bits that are NOT transmitted MUST be treated as if they
   are set to 0 on receipt.  Bits that are not supported by an
   implementation MUST be ignored on receipt.

   User Defined Application Identifier Bits have no relationship to
   Standard Application Identifier Bits and are NOT managed by IANA or
   any other standards body.  It is recommended that bits are used
   starting with Bit 0 so as to minimize the number of octets required
   to advertise all UDAs.

   If the link attribute advertisement is limited to be used by a
   specific set of applications, corresponding Bit-Masks MUST be present
   and application specific bit(s) MUST be set for all applications that
   use the link attributes advertised in the ASLA sub-TLV.

   Application Bit-Masks apply to all link attributes that support
   application specific values and are advertised in the ASLA sub-TLV.

   The advantage of not making the Application Bit-Masks part of the
   attribute advertisement itself is that the format of any previously
   defined link attributes can be kept and reused when advertising them
   in the ASLA sub-TLV.

   If the same attribute is advertised in more than single ASLA sub-TLVs
   with the application listed in the Application Bit-Masks, the
   application SHOULD use the first instance of advertisement and ignore
   any subsequent advertisements of that attribute.

   This document defines the initial set of link attributes that MUST
   use the ASLA sub-TLV if advertised in the OSPFv2 Extended Link TLV or
   in the OSPFv3 Router-Link TLV.  Documents which define new link
   attributes MUST state whether the new attributes support application
   specific values and as such MUST be advertised in an ASLA sub-TLV.
   The link attributes that MUST be advertised in ASLA sub-TLVs are:

      - Shared Risk Link Group [RFC4203]

      - Unidirectional Link Dela [RFC7471]

      - Min/Max Unidirectional Link Delay [RFC7471]



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      - Unidirectional Delay Variation [RFC7471]

      - Unidirectional Link Loss [RFC7471]

      - Unidirectional Residual Bandwidth [RFC7471]

      - Unidirectional Available Bandwidth [RFC7471]

      - Unidirectional Utilized Bandwidth [RFC7471]

      - Administrative Group [RFC3630]

      - Extended Administrative Group [RFC7308]

      - TE Metric [RFC3630]

6.  Reused TE link attributes

   This section defines the use case and indicates the code points
   (Section 14) from the OSPFv2 Extended Link TLV Sub-TLV Registry and
   OSPFv3 Extended LSA Sub-TLV Registry for some of the link attributes
   that have been originally defined for RSVP-TE or GMPLS.

6.1.  Shared Risk Link Group (SRLG)

   The SRLG of a link can be used in OSPF calculated IPFRR [RFC5714] to
   compute a backup path that does not share any SRLG group with the
   protected link.

   To advertise the SRLG of the link in the OSPFv2 Extended Link TLV,
   the same format for the sub-TLV defined in section 1.3 of [RFC4203]
   is used and TLV type 11 is used.  Similarly, for OSPFv3 to advertise
   the SRLG in the OSPFv3 Router-Link TLV, TLV type 12 is used.

6.2.  Extended Metrics

   [RFC3630] defines several link bandwidth types.  [RFC7471] defines
   extended link metrics that are based on link bandwidth, delay and
   loss characteristics.  All these can be used to compute primary and
   backup paths within an OSPF area to satisfy requirements for
   bandwidth, delay (nominal or worst case) or loss.

   To advertise extended link metrics in the OSPFv2 Extended Link TLV,
   the same format for the sub-TLVs defined in [RFC7471] is used with
   the following TLV types:

      12 - Unidirectional Link Delay




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      13 - Min/Max Unidirectional Link Delay

      14 - Unidirectional Delay Variation

      15 - Unidirectional Link Loss

      16 - Unidirectional Residual Bandwidth

      17 - Unidirectional Available Bandwidth

      18 - Unidirectional Utilized Bandwidth

   To advertise extended link metrics in the OSPFv3 Extended LSA Router-
   Link TLV, the same format for the sub-TLVs defined in [RFC7471] is
   used with the following TLV types:

      13 - Unidirectional Link Delay

      14 - Min/Max Unidirectional Link Delay

      15 - Unidirectional Delay Variation

      16 - Unidirectional Link Loss

      17 - Unidirectional Residual Bandwidth

      18 - Unidirectional Available Bandwidth

      19 - Unidirectional Utilized Bandwidth

6.3.  Administrative Group

   [RFC3630] and [RFC7308] define the Administrative Group and Extended
   Administrative Group sub-TLVs respectively.

   To advertise the Administrative Group and Extended Administrative
   Group in the OSPFv2 Extended Link TLV, the same format for the sub-
   TLVs defined in [RFC3630] and [RFC7308] is used with the following
   TLV types:

      19 - Administrative Group

      20 - Extended Administrative Group

   To advertise Administrative Group and Extended Administrative Group
   in the OSPFv3 Router-Link TLV, the same format for the sub-TLVs
   defined in [RFC3630] and [RFC7308] is used with the following TLV
   types:



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      20 - Administrative Group

      21 - Extended Administrative Group

6.4.  Traffic Engineering Metric

   [RFC3630] defines Traffic Engineering Metric.

   To advertise the Traffic Engineering Metric in the OSPFv2 Extended
   Link TLV, the same format for the sub-TLV defined in section 2.5.5 of
   [RFC3630] is used and TLV type 22 is used.  Similarly, for OSPFv3 to
   advertise the Traffic Engineering Metric in the OSPFv3 Router-Link
   TLV, TLV type 22 is used.

7.  Maximum Link Bandwidth

   Maximum link bandwidth is an application independent attribute of the
   link that is defined in [RFC3630].  Because it is an application
   independent attribute, it MUST NOT be advertised in ASLA sub-TLV.
   Instead, it MAY be advertised as a sub-TLV of the Extended Link
   Opaque LSA Extended Link TLV in OSPFv2 [RFC7684] or sub-TLV of OSPFv3
   E-Router-LSA Router-Link TLV in OSPFv3 [RFC8362].

   To advertise the Maximum link bandwidth in the OSPFv2 Extended Link
   TLV, the same format for sub-TLV defined in [RFC3630] is used with
   TLV type 23.

   To advertise the Maximum link bandwidth in the OSPFv3 Router-Link
   TLV, the same format for sub-TLV defined in [RFC3630] is used with
   TLV type 23.

8.  Considerations for Extended TE Metrics

   [RFC7471] defines a number of dynamic performance metrics associated
   with a link.  It is conceivable that such metrics could be measured
   specific to traffic associated with a specific application.
   Therefore this document includes support for advertising these link
   attributes specific to a given application.  However, in practice it
   may well be more practical to have these metrics reflect the
   performance of all traffic on the link regardless of application.  In
   such cases, advertisements for these attributes can be associated
   with all of the applications utilizing that link, for example, by
   listing all applications in the Application Bit-Mask.








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9.  Local Interface IPv6 Address Sub-TLV

   The Local Interface IPv6 Address Sub-TLV is an application
   independent attribute of the link that is defined in [RFC5329].
   Because it is an application independent attribute, it MUST NOT be
   advertised in the ASLA sub-TLV.  Instead, it MAY be advertised as a
   sub-TLV of the OSPFv3 E-Router-LSA Router-Link TLV [RFC8362].

   To advertise the Local Interface IPv6 Address Sub-TLV in the OSPFv3
   Router-Link TLV, the same format for sub-TLV defined in [RFC5329] is
   used with TLV type 24.

10.  Remote Interface IPv6 Address Sub-TLV

   The Remote Interface IPv6 Address Sub-TLV is an application
   independent attribute of the link that is defined in [RFC5329].
   Because it is an application independent attribute, it MUST NOT be
   advertised in the ASLA sub-TLV.  Instead, it MAY be advertised as a
   sub-TLV of the OSPFv3 E-Router-LSA Router-Link TLV [RFC8362].

   To advertise the Remote Interface IPv6 Address Sub-TLV in the OSPFv3
   Router-Link TLV, the same format for sub-TLV defined in [RFC5329] is
   used with TLV type 25.

11.  Attribute Advertisements and Enablement

   This document defines extensions to support the advertisement of
   application specific link attributes.

   Whether the presence of link attribute advertisements for a given
   application indicates that the application is enabled on that link
   depends upon the application.  Similarly, whether the absence of link
   attribute advertisements indicates that the application is not
   enabled depends upon the application.

   In the case of RSVP-TE, the advertisement of application specific
   link attributes has no implication of RSVP-TE being enabled on that
   link.  The RSVP-TE enablement is solely derived from the information
   carried in the OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3 Intra-Area-
   TE-LSA [RFC5329].

   In the case of SRTE, advertisement of application specific link
   attributes does NOT indicate enablement of SRTE.  The advertisements
   are only used to support constraints which may be applied when
   specifying an explicit path.  SRTE is implicitly enabled on all links
   which are part of the Segment Routing enabled topology independent of
   the existence of link attribute advertisements




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   In the case of LFA, advertisement of application specific link
   attributes does NOT indicate enablement of LFA on that link.
   Enablement is controlled by local configuration.

   If, in the future, additional standard applications are defined to
   use this mechanism, the specification defining this use MUST define
   the relationship between application specific link attribute
   advertisements and enablement for that application.

   This document allows the advertisement of application specific link
   attributes with no application identifiers i.e., both the Standard
   Application Identifier Bit Mask and the User Defined Application
   Identifier Bit Mask are not present (See Section 5).  This supports
   the use of the link attribute by any application.  In the presence of
   an application where the advertisement of link attribute
   advertisements is used to infer the enablement of an application on
   that link (e.g., RSVP-TE), the absence of the application identifier
   leaves ambiguous whether that application is enabled on such a link.
   This needs to be considered when making use of the "any application"
   encoding.

12.  Deployment Considerations

12.1.  Use of Legacy RSVP-TE LSA Advertisements

   Bit Identifiers for Standard Applications are defined in Section 5.
   All of the identifiers defined in this document are associated with
   applications which were already deployed in some networks prior to
   the writing of this document.  Therefore, such applications have been
   deployed using the RSVP-TE LSA advertisements.  The Standard
   Applications defined in this document MAY continue to use RSVP-TE LSA
   advertisements for a given link so long as at least one of the
   following conditions is true:

      The application is RSVP-TE

      The application is SRTE or LFA and RSVP-TE is not deployed
      anywhere in the network

      The application is SRTE or LFA, RSVP-TE is deployed in the
      network, and both the set of links on which SRTE and/or LFA
      advertisements are required and the attribute values used by SRTE
      and/or LFA on all such links is fully congruent with the links and
      attribute values used by RSVP-TE

   Under the conditions defined above, implementations which support the
   extensions defined in this document have the choice of using RSVP-TE
   LSA advertisements or application specific advertisements in support



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   of SRTE and/or LFA.  This will require implementations to provide
   controls specifying which type of advertisements are to be sent/
   processed on receive for these applications.  Further discussion of
   the associated issues can be found in Section 12.3.

   New applications which future documents define to make use of the
   advertisements defined in this document MUST NOT make use of RSVP-TE
   LSA advertisements.  This simplifies deployment of new applications
   by eliminating the need to support multiple ways to advertise
   attributes for the new applications.

12.2.  Use of Zero Length Application Identifier Bit Masks

   If link attributes are advertised associated with zero length
   Application Identifier Bit Masks for both standard applications and
   user defined applications, then any Standard Application and/or any
   User Defined Application is permitted to use that set of link
   attributes so long as there is not another set of attributes
   advertised on that same link which is associated with a non-zero
   length Application Identifier Bit Mask with a matching Application
   Identifier Bit set.  If support for a new application is introduced
   on any node in a network in the presence of such advertisements,
   these advertisements are permitted to be used by the new application.
   If this is not what is intended, then existing advertisements MUST be
   readvertised with an explicit set of applications specified before a
   new application is introduced.

12.3.  Interoperability, Backwards Compatibility and Migration Concerns

   Existing deployments of RSVP-TE, SRTE, and/or LFA utilize the legacy
   advertisements listed in Section 3.  Routers which do not support the
   extensions defined in this document will only process legacy
   advertisements and are likely to infer that RSVP-TE is enabled on the
   links for which legacy advertisements exist.  It is expected that
   deployments using the legacy advertisements will persist for a
   significant period of time.  Therefore deployments using the
   extensions defined in this document must be able to co-exist with use
   of the legacy advertisements by routers which do not support the
   extensions defined in this document.  The following sub-sections
   discuss interoperability and backwards compatibility concerns for a
   number of deployment scenarios.

12.3.1.  Multiple Applications: Common Attributes with RSVP-TE

   In cases where multiple applications are utilizing a given link, one
   of the applications is RSVP-TE, and all link attributes for a given
   link are common to the set of applications utilizing that link,
   interoperability is achieved by using legacy advertisements for RSVP-



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   TE.  Attributes for applications other than RSVP-TE MUST be
   advertised using application specific advertisements.  This results
   in duplicate advertisements for those attributes.

12.3.2.  Multiple Applications: Some Attributes Not Shared with RSVP-TE

   In cases where one or more applications other than RSVP-TE are
   utilizing a given link and one or more link attribute values are NOT
   shared with RSVP-TE, interoperability is achieved by using legacy
   advertisements for RSVP-TE.  Attributes for applications other than
   RSVP-TE MUST be advertised using application specific advertisements.
   In cases where some link attributes are shared with RSVP-TE, this
   requires duplicate advertisements for those attributes

12.3.3.  Interoperability with Legacy Routers

   For the applications defined in this document, routers which do not
   support the extensions defined in this document will send and receive
   only legacy link attribute advertisements.  So long as there is any
   legacy router in the network which has any of the applications
   enabled, all routers MUST continue to advertise link attributes using
   legacy advertisements.  In addition, the link attribute values
   associated with the set of applications supported by legacy routers
   (RSVP-TE, SRTE, and/or LFA) are always shared since legacy routers
   have no way of advertising or processing application specific values.
   Once all legacy routers have been upgraded, migration from legacy
   advertisements to application specific advertisements can be achieved
   via the following steps:

   1)Send application specific advertisements while continuing to
   advertise using legacy (all advertisements are then duplicated).
   Receiving routers continue to use legacy advertisements.

   2)Enable the use of the application specific advertisements on all
   routers

   3)Keep legacy advertisements if needed for RSVP-TE purposes.

   When the migration is complete, it then becomes possible to advertise
   incongruent values per application on a given link.

   Documents defining new applications which make use of the application
   specific advertisements defined in this document MUST discuss
   interoperability and backwards compatibility issues that could occur
   in the presence of routers which do not support the new application.






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12.3.4.  Use of Application Specific Advertisements for RSVP-TE

   The extensions defined in this document support RSVP-TE as one of the
   supported applications.  It is however RECOMMENDED to advertise all
   link-attributes for RSVP-TE in the existing OSPFv2 TE Opaque LSA
   [RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329] to maintain backward
   compatibility.  RSVP-TE can eventually utilize the application
   specific advertisements for newly defined link attributes, which are
   defined as application specific.

   Link attributes that are NOT allowed to be advertised in the ASLA
   Sub-TLV, such as Maximum Reservable Link Bandwidth and Unreserved
   Bandwidth MUST use the OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3
   Intra-Area-TE-LSA [RFC5329] and MUST NOT be advertised in ASLA Sub-
   TLV.

13.  Security Considerations

   Existing security extensions as described in [RFC2328], [RFC5340] and
   [RFC8362] apply to extensions defined in this document.  While OSPF
   is under a single administrative domain, there can be deployments
   where potential attackers have access to one or more networks in the
   OSPF routing domain.  In these deployments, stronger authentication
   mechanisms such as those specified in [RFC5709], [RFC7474], [RFC4552]
   or [RFC7166] SHOULD be used.

   Implementations must assure that malformed TLV and Sub-TLV defined in
   this document are detected and do not provide a vulnerability for
   attackers to crash the OSPF router or routing process.  Reception of
   a malformed TLV or Sub-TLV SHOULD be counted and/or logged for
   further analysis.  Logging of malformed TLVs and Sub-TLVs SHOULD be
   rate-limited to prevent a Denial of Service (DoS) attack (distributed
   or otherwise) from overloading the OSPF control plane.

   This document defines a new way to advertise link attributes.
   Tampering with the information defined in this document may have an
   effect on applications using it, including impacting Traffic
   Engineering.  This is similar in nature to the impacts associated
   with (for example) [RFC3630].  As the advertisements defined in this
   document limit the scope to specific applications, the impact of
   tampering is similarly limited in scope.

14.  IANA Considerations








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14.1.  OSPFv2

   The OSPFv2 Extended Link TLV Sub-TLVs registry [RFC7684] defines sub-
   TLVs at any level of nesting for OSPFv2 Extended Link TLVs.  IANA has
   assigned the following Sub-TLV types from the OSPFv2 Extended Link
   TLV Sub-TLVs Registry:

      10 - Application Specific Link Attributes

      11 - Shared Risk Link Group

      12 - Unidirectional Link Delay

      13 - Min/Max Unidirectional Link Delay

      14 - Unidirectional Delay Variation

      15 - Unidirectional Link Loss

      16 - Unidirectional Residual Bandwidth

      17 - Unidirectional Available Bandwidth

      18 - Unidirectional Utilized Bandwidth

      19 - Administrative Group

      20 - Extended Administrative Group

      22 - TE Metric

      23 - Maximum Link Bandwidth

14.2.  OSPFv3

   The OSPFv3 Extended LSA Sub-TLV Registry [RFC8362] defines sub-TLVs
   at any level of nesting for OSPFv3 Extended LSAs.  IANA has assigned
   the following Sub-TLV types from the OSPFv3 Extended LSA Sub-TLV
   Registry:

      11 - Application Specific Link Attributes

      12 - Shared Risk Link Group

      13 - Unidirectional Link Delay

      14 - Min/Max Unidirectional Link Delay




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      15 - Unidirectional Delay Variation

      16 - Unidirectional Link Loss

      16 - Unidirectional Residual Bandwidth

      18 - Unidirectional Available Bandwidth

      19 - Unidirectional Utilized Bandwidth

      20 - Administrative Group

      21 - Extended Administrative Group

      22 - TE Metric

      23 - Maximum Link Bandwidth

      24 - Local Interface IPv6 Address Sub-TLV

      25 - Remote Interface IPv6 Address Sub-TLV

15.  Contributors

   The following people contributed to the content of this document and
   should be considered as co-authors:

























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      Acee Lindem
      Cisco Systems
      301 Midenhall Way
      Cary, NC 27513
      USA

      Email: acee@cisco.com

      Ketan Talaulikar
      Cisco Systems, Inc.
      India

      Email: ketant@cisco.com

      Hannes Gredler
      RtBrick Inc.
      Austria

      Email: hannes@rtbrick.com


16.  Acknowledgments

   Thanks to Chris Bowers for his review and comments.

   Thanks to Alvaro Retana for his detailed review and comments.

17.  References

17.1.  Normative References

   [I-D.ietf-isis-te-app]
              Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
              J. Drake, "IS-IS TE Attributes per application", draft-
              ietf-isis-te-app-12 (work in progress), March 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.







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   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
              <https://www.rfc-editor.org/info/rfc4203>.

   [RFC5329]  Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
              "Traffic Engineering Extensions to OSPF Version 3",
              RFC 5329, DOI 10.17487/RFC5329, September 2008,
              <https://www.rfc-editor.org/info/rfc5329>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC7308]  Osborne, E., "Extended Administrative Groups in MPLS
              Traffic Engineering (MPLS-TE)", RFC 7308,
              DOI 10.17487/RFC7308, July 2014,
              <https://www.rfc-editor.org/info/rfc7308>.

   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
              <https://www.rfc-editor.org/info/rfc7471>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

17.2.  Informative References







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   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-06 (work in progress),
              December 2019.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <https://www.rfc-editor.org/info/rfc5286>.

   [RFC5709]  Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
              Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
              Authentication", RFC 5709, DOI 10.17487/RFC5709, October
              2009, <https://www.rfc-editor.org/info/rfc5709>.

   [RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",
              RFC 5714, DOI 10.17487/RFC5714, January 2010,
              <https://www.rfc-editor.org/info/rfc5714>.

   [RFC7166]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
              Authentication Trailer for OSPFv3", RFC 7166,
              DOI 10.17487/RFC7166, March 2014,
              <https://www.rfc-editor.org/info/rfc7166>.

   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
              <https://www.rfc-editor.org/info/rfc7474>.

Authors' Addresses











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   Peter Psenak (editor)
   Cisco Systems
   Eurovea Centre, Central 3
   Pribinova Street 10
   Bratislava  81109
   Slovakia

   Email: ppsenak@cisco.com


   Les Ginsberg
   Cisco Systems
   821 Alder Drive
   MILPITAS, CA  95035
   USA

   Email: ginsberg@cisco.com


   Wim Henderickx
   Nokia
   Copernicuslaan 50
   Antwerp, 2018  94089
   Belgium

   Email: wim.henderickx@nokia.com


   Jeff Tantsura
   Apstra
   US

   Email: jefftant.ietf@gmail.com


   John Drake
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, California  94089
   USA

   Email: jdrake@juniper.net









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