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rfc:rfc8570

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.

Ginsberg, et al. Standards Track [Page 1] RFC 8570 IS-IS TE Metric Extensions March 2019

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.

Ginsberg, et al. Standards Track [Page 2] 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.

Ginsberg, et al. Standards Track [Page 3] RFC 8570 IS-IS TE Metric Extensions March 2019

 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.

Ginsberg, et al. Standards Track [Page 4] RFC 8570 IS-IS TE Metric Extensions March 2019

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

Ginsberg, et al. Standards Track [Page 5] RFC 8570 IS-IS TE Metric Extensions March 2019

 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.

Ginsberg, et al. Standards Track [Page 6] RFC 8570 IS-IS TE Metric Extensions March 2019

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.

Ginsberg, et al. Standards Track [Page 7] RFC 8570 IS-IS TE Metric Extensions March 2019

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.

Ginsberg, et al. Standards Track [Page 8] RFC 8570 IS-IS TE Metric Extensions March 2019

 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.

Ginsberg, et al. Standards Track [Page 9] RFC 8570 IS-IS TE Metric Extensions March 2019

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.

Ginsberg, et al. Standards Track [Page 10] RFC 8570 IS-IS TE Metric Extensions March 2019

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).

Ginsberg, et al. Standards Track [Page 11] RFC 8570 IS-IS TE Metric Extensions March 2019

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.

Ginsberg, et al. Standards Track [Page 12] RFC 8570 IS-IS TE Metric Extensions March 2019

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.

Ginsberg, et al. Standards Track [Page 13] RFC 8570 IS-IS TE Metric Extensions March 2019

 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.

Ginsberg, et al. Standards Track [Page 14] RFC 8570 IS-IS TE Metric Extensions March 2019

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.

Ginsberg, et al. Standards Track [Page 15] RFC 8570 IS-IS TE Metric Extensions March 2019

 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

Ginsberg, et al. Standards Track [Page 16] RFC 8570 IS-IS TE Metric Extensions March 2019

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>.

Ginsberg, et al. Standards Track [Page 17] RFC 8570 IS-IS TE Metric Extensions March 2019

 [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>.

Ginsberg, et al. Standards Track [Page 18] RFC 8570 IS-IS TE Metric Extensions March 2019

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.

Ginsberg, et al. Standards Track [Page 19] RFC 8570 IS-IS TE Metric Extensions March 2019

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

Ginsberg, et al. Standards Track [Page 20] RFC 8570 IS-IS TE Metric Extensions March 2019

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

Ginsberg, et al. Standards Track [Page 21]

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