IS-IS Traffic Engineering (TE) Metric Extensions
RFC 8570

Internet Engineering Task Force (IETF)                  L. Ginsberg, Ed.
Request for Comments: 8570                           Cisco Systems, Inc.
Obsoletes: 7810                                          S. Previdi, Ed.
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                             S. Giacalone
                                                               Microsoft
                                                                 D. Ward
                                                     Cisco Systems, Inc.
                                                                J. Drake
                                                        Juniper Networks
                                                                   Q. Wu
                                                                  Huawei
                                                              March 2019

            IS-IS Traffic Engineering (TE) Metric Extensions

Abstract

   In certain networks, such as, but not limited to, financial
   information networks (e.g., stock market data providers), network-
   performance criteria (e.g., latency) are becoming as critical to
   data-path selection as other metrics.

   This document describes extensions to IS-IS Traffic Engineering
   Extensions (RFC 5305).  These extensions provide a way to distribute
   and collect network-performance information in a scalable fashion.
   The information distributed using IS-IS TE Metric Extensions can then
   be used to make path-selection decisions based on network
   performance.

   Note that this document only covers the mechanisms with which
   network-performance information is distributed.  The mechanisms for
   measuring network performance or acting on that information, once
   distributed, are outside the scope of this document.

   This document obsoletes RFC 7810.

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Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8570.

Copyright Notice

   Copyright (c) 2019 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.

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RFC 8570               IS-IS TE Metric Extensions             March 2019

Table of Contents

   1. Introduction ....................................................3
      1.1. Requirements Language ......................................4
   2. TE Metric Extensions to IS-IS ...................................5
   3. Interface and Neighbor Addresses ................................6
   4. Sub-TLV Details .................................................7
      4.1. Unidirectional Link Delay Sub-TLV ..........................7
      4.2. Min/Max Unidirectional Link Delay Sub-TLV ..................8
      4.3. Unidirectional Delay Variation Sub-TLV .....................9
      4.4. Unidirectional Link Loss Sub-TLV ..........................10
      4.5. Unidirectional Residual Bandwidth Sub-TLV .................11
      4.6. Unidirectional Available Bandwidth Sub-TLV ................12
      4.7. Unidirectional Utilized Bandwidth Sub-TLV .................13
   5. Announcement Thresholds and Filters ............................13
   6. Announcement Suppression .......................................14
   7. Network Stability and Announcement Periodicity .................15
   8. Enabling and Disabling Sub-TLVs ................................15
   9. Static Metric Override .........................................15
   10. Compatibility .................................................15
   11. Security Considerations .......................................15
   12. IANA Considerations ...........................................16
   13. References ....................................................17
      13.1. Normative References .....................................17
      13.2. Informative References ...................................18
   Appendix A. Changes from RFC 7810 .................................19
   Acknowledgements ..................................................20
   Contributors ......................................................20
   Authors' Addresses ................................................21

1.  Introduction

   In certain networks, such as, but not limited to, financial
   information networks (e.g., stock market data providers), network-
   performance information (e.g., latency) is becoming as critical to
   data-path selection as other metrics.

   In these networks, extremely large amounts of money rest on the
   ability to access market data in "real time" and to predictably make
   trades faster than the competition.  Because of this, using metrics
   such as hop count or cost as routing metrics is becoming only
   tangentially important.  Rather, it would be beneficial to be able to
   make path-selection decisions based on performance data (such as
   latency) in a cost-effective and scalable way.

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   This document describes extensions (hereafter called "IS-IS TE Metric
   Extensions") to the Extended IS Reachability TLV defined in
   [RFC5305]; these extensions can be used to distribute network-
   performance information (such as link delay, delay variation, packet
   loss, residual bandwidth, and available bandwidth).

   The data distributed by the IS-IS TE Metric Extensions described in
   this document is meant to be used as part of the operation of the
   routing protocol (e.g., by replacing cost with latency or considering
   bandwidth as well as cost), to enhance Constrained Shortest Path
   First (CSPF), or for other uses such as supplementing the data used
   by an Application-Layer Traffic Optimization (ALTO) server [RFC7285].
   With respect to CSPF, the data distributed by IS-IS TE Metric
   Extensions can be used to set up, fail over, and fail back data paths
   using protocols such as RSVP-TE [RFC3209].

   Note that the mechanisms described in this document only disseminate
   performance information.  The methods for initially gathering that
   performance information (such as the methods described in [RFC6375])
   or how to act on the information once it is distributed are outside
   the scope of this document.  Example mechanisms to measure latency,
   delay variation, and loss in an MPLS network are given in [RFC6374].
   While this document does not specify how the performance information
   should be obtained, the measurement of delay SHOULD NOT vary
   significantly based upon the offered traffic load.  Thus, queuing
   delays SHOULD NOT be included in the delay measurement.  For links
   such as forwarding adjacencies [RFC4206], care must be taken that
   measurement of the associated delay avoids significant queuing
   delays; that could be accomplished in a variety of ways, including
   either (1) measuring with a traffic class that experiences minimal
   queuing or (2) summing the measured link delays of the components of
   the link's path.

   This document obsoletes [RFC7810].

1.1.  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.

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2.  TE Metric Extensions to IS-IS

   This document registers new IS-IS TE sub-TLVs in the "Sub-TLVs for
   TLVs 22, 23, 141, 222, and 223" registry.  These new sub-TLVs provide
   ways to distribute network-performance information.  The extensions
   in this document build on the extensions provided in IS-IS TE
   [RFC5305] and GMPLS [RFC4203].

   The Extended IS Reachability TLV (type 22) (defined in [RFC5305]),
   Inter-AS Reachability TLV (also called "inter-AS reachability
   information TLV") (type 141) (defined in [RFC5316]), and MT-ISN TLV
   (type 222) (defined in [RFC5120]) have nested sub-TLVs that permit
   the TLVs to be readily extended.  This document registers several
   sub-TLVs:

      Type    Description
      ----------------------------------------------------
       33     Unidirectional Link Delay

       34     Min/Max Unidirectional Link Delay

       35     Unidirectional Delay Variation

       36     Unidirectional Link Loss

       37     Unidirectional Residual Bandwidth

       38     Unidirectional Available Bandwidth

       39     Unidirectional Utilized Bandwidth

   As can be seen in the list above, the sub-TLVs described in this
   document carry different types of network-performance information.
   The new sub-TLVs include a bit called the Anomalous (or "A") bit.
   When the A bit is clear (or when the sub-TLV does not include an
   A bit), the sub-TLV describes steady-state link performance.  This
   information could conceivably be used to construct a steady-state
   performance topology for initial tunnel-path computation or to verify
   alternative failover paths.

   When network performance violates configurable link-local thresholds,
   a sub-TLV with the A bit set is advertised.  That sub-TLV could be
   used by the receiving node to determine whether to (1) fail traffic
   to a backup path or (2) calculate an entirely new path.  From an MPLS
   perspective, the intent of the A bit is to permit label switched path
   ingress nodes to determine whether the link referenced in the sub-TLV
   affects any of the label switched paths for which it is ingress.  If

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   they are affected, then they can determine whether those label
   switched paths still meet end-to-end performance objectives.  If not,
   then the node could conceivably move affected traffic to a
   pre-established protection label switched path or establish a new
   label switched path and place the traffic in it.

   If link performance then improves beyond a configurable minimum value
   (reuse threshold), that sub-TLV can be re-advertised with the A bit
   cleared.  In this case, a receiving node can conceivably do whatever
   re-optimization (or failback) it wishes to do (including nothing).

   Note that when a sub-TLV does not include the A bit, that sub-TLV
   cannot be used for failover purposes.  The A bit was intentionally
   omitted from some sub-TLVs to help mitigate oscillations.  See
   Section 5 for more information.

   Consistent with the existing IS-IS TE specification [RFC5305], the
   bandwidth advertisements defined in this document MUST be encoded as
   IEEE floating-point values [IEEE754].  The delay and delay-variation
   advertisements defined in this document MUST be encoded as integer
   values.  Delay values MUST be quantified in units of microseconds,
   packet loss MUST be quantified as a percentage of packets sent, and
   bandwidth MUST be sent as bytes per second.  All values (except
   residual bandwidth) MUST be calculated as rolling averages, where the
   averaging period MUST be a configurable period of time.  See
   Section 5 for more information.

3.  Interface and Neighbor Addresses

   The use of IS-IS TE Metric Extensions sub-TLVs is not confined to the
   TE context.  In other words, IS-IS TE Metric Extensions sub-TLVs
   defined in this document can also be used for computing paths in the
   absence of a TE subsystem.

   However, as for the TE case, Interface Address and Neighbor Address
   sub-TLVs (IPv4 or IPv6) MUST be present.  The encoding is defined in
   [RFC5305] for IPv4 and in [RFC6119] for IPv6.

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4.  Sub-TLV Details

4.1.  Unidirectional Link Delay Sub-TLV

   This sub-TLV advertises the average link delay between two directly
   connected IS-IS neighbors.  The delay advertised by this sub-TLV MUST
   be the delay from the local neighbor to the remote neighbor (i.e.,
   the forward-path latency).  The format of this sub-TLV is shown in
   the following diagram:

     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    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |A|  RESERVED   |                   Delay                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 1

   where:

   Type:  33

   Length:  4

   A bit:  This field represents the Anomalous (A) bit.  The A bit is
      set when the measured value of this parameter exceeds its
      configured maximum threshold.  The A bit is cleared when the
      measured value falls below its configured reuse threshold.  If the
      A bit is cleared, the sub-TLV represents steady-state link
      performance.

   RESERVED:  This field is reserved for future use.  It MUST be set
      to 0 when sent and MUST be ignored when received.

   Delay:  This 24-bit field carries the average link delay over a
      configurable interval in microseconds, encoded as an integer
      value.  When set to the maximum value 16,777,215
      (16.777215 seconds), then the delay is at least that value and may
      be larger.

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4.2.  Min/Max Unidirectional Link Delay Sub-TLV

   This sub-TLV advertises the minimum and maximum delay values between
   two directly connected IS-IS neighbors.  The delay advertised by this
   sub-TLV MUST be the delay from the local neighbor to the remote
   neighbor (i.e., the forward-path latency).  The format of this
   sub-TLV is shown in the following diagram:

     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    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |A| RESERVED    |                   Min Delay                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   RESERVED    |                   Max Delay                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 2

   where:

   Type:  34

   Length:  8

   A bit:  This field represents the Anomalous (A) bit.  The A bit is
      set when one or more measured values exceed a configured maximum
      threshold.  The A bit is cleared when the measured value falls
      below its configured reuse threshold.  If the A bit is cleared,
      the sub-TLV represents steady-state link performance.

   RESERVED:  This field is reserved for future use.  It MUST be set
      to 0 when sent and MUST be ignored when received.

   Min Delay:  This 24-bit field carries the minimum measured link delay
      value (in microseconds) over a configurable interval, encoded as
      an integer value.

   Max Delay:  This 24-bit field carries the maximum measured link delay
      value (in microseconds) over a configurable interval, encoded as
      an integer value.

   Implementations MAY also permit the configuration of an offset value
   (in microseconds) to be added to the measured delay value, to
   facilitate the communication of operator-specific delay constraints.

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   It is possible for Min Delay and Max Delay to be the same value.

   When the delay value (Min Delay or Max Delay) is set to the maximum
   value 16,777,215 (16.777215 seconds), then the delay is at least that
   value and may be larger.

4.3.  Unidirectional Delay Variation Sub-TLV

   This sub-TLV advertises the average link delay variation between two
   directly connected IS-IS neighbors.  The delay variation advertised
   by this sub-TLV MUST be the delay from the local neighbor to the
   remote neighbor (i.e., the forward-path latency).  The format of this
   sub-TLV is shown in the following diagram:

     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    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  RESERVED     |               Delay Variation                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 3

   where:

   Type:  35

   Length:  4

   RESERVED:  This field is reserved for future use.  It MUST be set
      to 0 when sent and MUST be ignored when received.

   Delay Variation:  This 24-bit field carries the average link delay
      variation over a configurable interval in microseconds, encoded as
      an integer value.  When set to 0, it has not been measured.  When
      set to the maximum value 16,777,215 (16.777215 seconds), then the
      delay is at least that value and may be larger.

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4.4.  Unidirectional Link Loss Sub-TLV

   This sub-TLV advertises the loss (as a packet percentage) between two
   directly connected IS-IS neighbors.  The link loss advertised by this
   sub-TLV MUST be the packet loss from the local neighbor to the remote
   neighbor (i.e., the forward-path loss).  The format of this sub-TLV
   is shown in the following diagram:

     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    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |A|  RESERVED   |                    Link Loss                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 4

   where:

   Type:  36

   Length:  4

   A bit:  This field represents the Anomalous (A) bit.  The A bit is
      set when the measured value of this parameter exceeds its
      configured maximum threshold.  The A bit is cleared when the
      measured value falls below its configured reuse threshold.  If the
      A bit is cleared, the sub-TLV represents steady-state link
      performance.

   RESERVED:  This field is reserved for future use.  It MUST be set
      to 0 when sent and MUST be ignored when received.

   Link Loss:  This 24-bit field carries link packet loss as a
      percentage of the total traffic sent over a configurable interval.
      The basic unit is 0.000003%, where (2^24 - 2) is 50.331642%.  This
      value is the highest packet-loss percentage that can be expressed
      (the assumptions being that (1) precision is more important on
      high-speed links than the ability to advertise loss rates greater
      than this and (2) high-speed links with over 50% loss are
      unusable).  Therefore, measured values that are larger than the
      field maximum SHOULD be encoded as the maximum value.

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4.5.  Unidirectional Residual Bandwidth Sub-TLV

   This sub-TLV advertises the residual bandwidth between two directly
   connected IS-IS neighbors.  The residual bandwidth advertised by this
   sub-TLV MUST be the residual bandwidth from the system originating
   the Link State Advertisement (LSA) to its neighbor.

     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    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Residual Bandwidth                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 5

   where:

   Type:  37

   Length:  4

   Residual Bandwidth:  This field carries the residual bandwidth on a
      link, forwarding adjacency [RFC4206], or bundled link in IEEE
      floating-point format with units of bytes per second.  For a link
      or forwarding adjacency, residual bandwidth is defined to be the
      maximum bandwidth [RFC5305] minus the bandwidth currently
      allocated to RSVP-TE label switched paths.  For a bundled link,
      residual bandwidth is defined to be the sum of the component link
      residual bandwidths.

      The calculation of residual bandwidth is different than that of
      unreserved bandwidth [RFC5305].  This calculation subtracts tunnel
      reservations from maximum bandwidth (i.e., the link capacity)
      [RFC5305] and provides an aggregated remainder across priorities.
      Unreserved bandwidth, on the other hand, is subtracted from the
      maximum reservable bandwidth (the bandwidth that can theoretically
      be reserved) and provides per-priority remainders.  Residual
      bandwidth and unreserved bandwidth [RFC5305] can be used
      concurrently, and each has a separate use case (e.g., the former
      can be used for applications like Weighted ECMP, while the latter
      can be used for call admission control).

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4.6.  Unidirectional Available Bandwidth Sub-TLV

   This sub-TLV advertises the available bandwidth between two directly
   connected IS-IS neighbors.  The available bandwidth advertised by
   this sub-TLV MUST be the available bandwidth from the system
   originating this sub-TLV.  The format of this sub-TLV is shown in the
   following diagram:

     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    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Available Bandwidth                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 6

   where:

   Type:  38

   Length:  4

   Available Bandwidth:  This field carries the available bandwidth on a
      link, forwarding adjacency, or bundled link in IEEE floating-point
      format with units of bytes per second.  For a link or forwarding
      adjacency, available bandwidth is defined to be residual bandwidth
      (see Section 4.5) minus the measured bandwidth used for the actual
      forwarding of non-RSVP-TE label switched path packets.  For a
      bundled link, available bandwidth is defined to be the sum of the
      component link available bandwidths.

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4.7.  Unidirectional Utilized Bandwidth Sub-TLV

   This sub-TLV advertises the bandwidth utilization between two
   directly connected IS-IS neighbors.  The bandwidth utilization
   advertised by this sub-TLV MUST be the bandwidth from the system
   originating this sub-TLV.  The format of this sub-TLV is shown in the
   following diagram:

     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    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Utilized Bandwidth                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 7

   where:

   Type:  39

   Length:  4

   Utilized Bandwidth:  This field carries the bandwidth utilization on
      a link, forwarding adjacency, or bundled link in IEEE
      floating-point format with units of bytes per second.  For a link
      or forwarding adjacency, bandwidth utilization represents the
      actual utilization of the link (i.e., as measured by the
      advertising node).  For a bundled link, bandwidth utilization is
      defined to be the sum of the component link bandwidth
      utilizations.

5.  Announcement Thresholds and Filters

   The values advertised in all sub-TLVs (except minimum/maximum delay
   and residual bandwidth) MUST represent an average over a period of
   time or be obtained by a filter that is reasonably representative of
   an average.  For example, a rolling average is one such filter.

   Minimum and maximum delay MUST each be derived in one of the
   following ways: by taking the lowest and/or highest measured value
   over a measurement interval or by making use of a filter or other
   technique to obtain a reasonable representation of a minimum value
   and a maximum value representative of the interval, with compensation
   for outliers.

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   The measurement interval, any filter coefficients, and any
   advertisement intervals MUST be configurable per sub-TLV.

   In addition to the measurement intervals governing re-advertisement,
   implementations SHOULD provide configurable accelerated advertisement
   thresholds per sub-TLV, such that:

   1.  If the measured parameter falls outside a configured upper bound
       for all but the minimum delay metric (or lower bound for the
       minimum delay metric only) and the advertised sub-TLV is not
       already outside that bound, or

   2.  If the difference between the last advertised value and current
       measured value exceeds a configured threshold, then

   3.  The advertisement is made immediately.

   4.  For sub-TLVs that include an A bit, an additional threshold
       SHOULD be included corresponding to the threshold for which the
       performance is considered anomalous (and sub-TLVs with the A bit
       are sent).  The A bit is cleared when the sub-TLV's performance
       has been below (or re-crosses) this threshold for one or more
       advertisement intervals to permit failback.

   To prevent oscillations, only the high threshold or the low threshold
   (but not both) may be used to trigger any given sub-TLV that
   supports both.

   Additionally, once outside the bounds of the threshold, any
   re-advertisement of a measurement within the bounds would remain
   governed solely by the measurement interval for that sub-TLV.

6.  Announcement Suppression

   When link-performance values change by small amounts that fall under
   thresholds that would cause the announcement of a sub-TLV,
   implementations SHOULD suppress sub-TLV re-advertisement and/or
   lengthen the period within which the sub-TLVs are refreshed.

   Only the accelerated advertisement threshold mechanism described in
   Section 5 may shorten the re-advertisement interval.  All suppression
   and re-advertisement interval backoff timer features SHOULD be
   configurable.

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7.  Network Stability and Announcement Periodicity

   Sections 5 and 6 provide configurable mechanisms to bound the number
   of re-advertisements.  Instability might occur in very large networks
   if measurement intervals are set low enough to overwhelm the
   processing of flooded information at some of the routers in the
   topology.  Therefore, care should be taken in setting these values.

   Additionally, the default measurement interval for all sub-TLVs
   SHOULD be 30 seconds.

   Announcements MUST also be able to be throttled using configurable
   inter-update throttle timers.  The minimum announcement periodicity
   is one announcement per second.  The default value SHOULD be set to
   120 seconds.

   Implementations SHOULD NOT permit the inter-update timer to be lower
   than the measurement interval.

   Furthermore, it is RECOMMENDED that any underlying performance-
   measurement mechanisms not include any significant buffer delay, any
   significant buffer-induced delay variation, or any significant loss
   due to buffer overflow or due to active queue management.

8.  Enabling and Disabling Sub-TLVs

   Implementations MUST make it possible to individually enable or
   disable each sub-TLV based on configuration.

9.  Static Metric Override

   Implementations SHOULD permit static configuration and/or manual
   override of dynamic measurements for each sub-TLV in order to
   simplify migration and to mitigate scenarios where dynamic
   measurements are not possible.

10.  Compatibility

   As per [RFC5305], unrecognized sub-TLVs should be silently ignored.

11.  Security Considerations

   The sub-TLVs introduced in this document allow an operator to
   advertise state information of links (bandwidth, delay) that could be
   sensitive and that an operator may not want to disclose.

   Section 7 describes a mechanism to ensure network stability when the
   new sub-TLVs defined in this document are advertised.

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   Implementations SHOULD follow the described guidelines to mitigate
   the risk of instability.

   [RFC5304] describes an authentication method for IS-IS Link State
   PDUs that allows cryptographic authentication of IS-IS Link State
   PDUs.

   It is anticipated that in most deployments, the IS-IS protocol is
   used within an infrastructure entirely under the control of the same
   operator.  However, it is worth considering that the effect of
   sending IS-IS Traffic Engineering sub-TLVs over insecure links could
   include a man-in-the-middle attacker delaying real-time data to a
   given site or destination; this could negatively affect the value of
   the data for that site or destination.  The use of Link State PDU
   cryptographic authentication allows mitigation of the risk of
   man-in-the-middle attacks.

12.  IANA Considerations

   IANA maintains the registry for the sub-TLVs.  IANA has registered
   the following sub-TLVs in the "Sub-TLVs for TLVs 22, 23, 141, 222,
   and 223" registry:

      Type    Description
      ----------------------------------------------------
       33     Unidirectional Link Delay

       34     Min/Max Unidirectional Link Delay

       35     Unidirectional Delay Variation

       36     Unidirectional Link Loss

       37     Unidirectional Residual Bandwidth

       38     Unidirectional Available Bandwidth

       39     Unidirectional Utilized Bandwidth

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13.  References

13.1.  Normative References

   [IEEE754]  Institute of Electrical and Electronics Engineers, "IEEE
              Standard for Floating-Point Arithmetic", IEEE
              Std 754-2008.

   [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>.

   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
              Hierarchy with Generalized Multi-Protocol Label Switching
              (GMPLS) Traffic Engineering (TE)", RFC 4206,
              DOI 10.17487/RFC4206, October 2005,
              <https://www.rfc-editor.org/info/rfc4206>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304,
              October 2008, <https://www.rfc-editor.org/info/rfc5304>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305,
              October 2008, <https://www.rfc-editor.org/info/rfc5305>.

   [RFC5316]  Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316,
              December 2008, <https://www.rfc-editor.org/info/rfc5316>.

   [RFC6119]  Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
              Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119,
              February 2011, <https://www.rfc-editor.org/info/rfc6119>.

   [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>.

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   [RFC7810]  Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and
              Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions",
              RFC 7810, DOI 10.17487/RFC7810, May 2016,
              <https://www.rfc-editor.org/info/rfc7810>.

   [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>.

13.2.  Informative References

   [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>.

   [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>.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,
              <https://www.rfc-editor.org/info/rfc6374>.

   [RFC6375]  Frost, D., Ed. and S. Bryant, Ed., "A Packet Loss and
              Delay Measurement Profile for MPLS-Based Transport
              Networks", RFC 6375, DOI 10.17487/RFC6375, September 2011,
              <https://www.rfc-editor.org/info/rfc6375>.

   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.

   [RFC8571]  Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
              C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
              IGP Traffic Engineering Performance Metric Extensions",
              RFC 8571, DOI 10.17487/RFC8571, March 2019,
              <https://www.rfc-editor.org/info/rfc8571>.

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Appendix A.  Changes from RFC 7810

   Errata ID 5293 (https://www.rfc-editor.org/errata/eid5293) correctly
   identified that in [RFC7810] the length associated with the following
   sub-TLVs did not match the figures associated with each:

      37    Unidirectional Residual Bandwidth

      38    Unidirectional Available Bandwidth

      39    Unidirectional Utilized Bandwidth

   The length specified was 4, which did not include the RESERVED field
   shown in the figures.  Subsequent investigation revealed that some
   implementations had used the specified length (4) and omitted the
   RESERVED field while other implementations included the specified
   RESERVED field and used a length of 5.

   Because these different implementation choices are not interoperable,
   it was decided that a bis version should be generated to resolve this
   ambiguity.

   The choice made here is to omit the unused RESERVED field from these
   sub-TLVs and use the length of 4.  This matches the corresponding
   advertisements specified in the equivalent OSPF TE specification
   [RFC7471] and the corresponding BGP - Link State (BGP-LS)
   specification [RFC8571].

   Some minor editorial corrections have also been made.

   Errata ID 5486 (https://www.rfc-editor.org/errata/eid5486) identified
   that in Section 4.6 of [RFC7810] the definition of available
   bandwidth on bundled links used a circular definition, i.e., it used
   "sum of the component link available bandwidths" when it should have
   used "sum of the component link residual bandwidths".  This has been
   corrected and clarified.

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Acknowledgements

   In [RFC7810], the authors recognized Ayman Soliman, Nabil Bitar,
   David McDysan, Edward Crabbe, Don Fedyk, Hannes Gredler, Uma
   Chunduri, Alvaro Retana, Brian Weis, and Barry Leiba for their
   contributions and reviews of this document.

   The authors also recognized Curtis Villamizar for significant
   comments and direct content collaboration.

   For this document, the authors thank Jeff Haas for identifying and
   reporting the incorrect encoding of the bandwidth-related sub-TLVs.

Contributors

   The following people contributed substantially to the content of this
   document and should be considered coauthors:

      Alia Atlas
      Juniper Networks
      United States of America
      Email: akatlas@juniper.net

      Clarence Filsfils
      Cisco Systems, Inc.
      Belgium
      Email: cfilsfil@cisco.com

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Authors' Addresses

   Les Ginsberg (editor)
   Cisco Systems, Inc.

   Email: ginsberg@cisco.com

   Stefano Previdi (editor)
   Huawei

   Email: stefano@previdi.net

   Spencer Giacalone
   Microsoft

   Email: spencer.giacalone@gmail.com

   Dave Ward
   Cisco Systems, Inc.

   Email: wardd@cisco.com

   John Drake
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   United States of America

   Email: jdrake@juniper.net

   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: bill.wu@huawei.com

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