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Internet Engineering Task Force (IETF)                   S. Previdi, Ed.Request for Comments: 7810                           Cisco Systems, Inc.Category: Standards Track                                   S. GiacaloneISSN: 2070-1721                                                Microsoft                                                                 D. Ward                                                     Cisco Systems, Inc.                                                                J. Drake                                                        Juniper Networks                                                                   Q. Wu                                                                  Huawei                                                                May 2016IS-IS Traffic Engineering (TE) Metric ExtensionsAbstract   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) such that network-performance information can   be distributed and collected 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.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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7810.Previdi, et al.              Standards Track                    [Page 1]

RFC 7810               IS-IS TE Metric Extensions               May 2016Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .31.1.  Conventions Used in This Document . . . . . . . . . . . .42.  TE Metric Extensions to IS-IS . . . . . . . . . . . . . . . .43.  Interface and Neighbor Addresses  . . . . . . . . . . . . . .54.  Sub-TLV Details . . . . . . . . . . . . . . . . . . . . . . .64.1.  Unidirectional Link Delay Sub-TLV . . . . . . . . . . . .64.2.  Min/Max Unidirectional Link Delay Sub-TLV . . . . . . . .74.3.  Unidirectional Delay Variation Sub-TLV  . . . . . . . . .84.4.  Unidirectional Link Loss Sub-TLV  . . . . . . . . . . . .94.5.  Unidirectional Residual Bandwidth Sub-TLV . . . . . . . .104.6.  Unidirectional Available Bandwidth Sub-TLV  . . . . . . .114.7.  Unidirectional Utilized Bandwidth Sub-TLV . . . . . . . .125.  Announcement Thresholds and Filters . . . . . . . . . . . . .126.  Announcement Suppression  . . . . . . . . . . . . . . . . . .137.  Network Stability and Announcement Periodicity  . . . . . . .148.  Enabling and Disabling Sub-TLVs . . . . . . . . . . . . . . .149.  Static Metric Override  . . . . . . . . . . . . . . . . . . .1410. Compatibility . . . . . . . . . . . . . . . . . . . . . . . .1411. Security Considerations . . . . . . . . . . . . . . . . . . .1512. IANA Considerations . . . . . . . . . . . . . . . . . . . . .1513. References  . . . . . . . . . . . . . . . . . . . . . . . . .1613.1.  Normative References . . . . . . . . . . . . . . . . . .1613.2.  Informative References . . . . . . . . . . . . . . . . .16   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .17   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .17   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .18Previdi, et al.              Standards Track                    [Page 2]

RFC 7810               IS-IS TE Metric Extensions               May 20161.  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.   This document describes extensions (hereafter called "IS-IS TE Metric   Extensions") to the IS-IS Extended Reachability TLV defined in   [RFC5305], that 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 proposed 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-SPF (CSPF), or for   other uses such as supplementing the data used by an 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 described in [RFC6375], or acting on   it 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,   care must be taken that measurement of the associated delay avoids   significant queuing delay; that could be accomplished in a variety of   ways, including either by measuring with a traffic class that   experiences minimal queuing or by summing the measured link delays of   the components of the link's path.Previdi, et al.              Standards Track                    [Page 3]

RFC 7810               IS-IS TE Metric Extensions               May 20161.1.  Conventions Used in This Document   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [RFC2119].   In this document, these words will appear with that interpretation   only when in ALL CAPS.  Lowercase uses of these words are not to be   interpreted as carrying the significance described inRFC 2119.2.  TE Metric Extensions to IS-IS   This document registers new IS-IS TE sub-TLVs that can be announced   in the "Sub-TLVs for TLVs 22, 23, 141, 222, and 223" registry in   order to distribute network-performance information.  The extensions   in this document build on the ones provided in IS-IS TE [RFC5305] and   GMPLS [RFC4203].   IS-IS Extended Reachability TLV 22 (defined in [RFC5305]), Inter-AS   Reachability Information TLV 141 (defined in [RFC5316]), and MT-ISIS   TLV 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.Previdi, et al.              Standards Track                    [Page 4]

RFC 7810               IS-IS TE Metric Extensions               May 2016   When network performance violates configurable link-local thresholds,   a sub-TLV with the A bit set is advertised.  These sub-TLVs could be   used by the receiving node to determine whether to fail traffic to a   backup path or whether to 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 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.  SeeSection 5 for more information.   Consistent with existing IS-IS TE specification [RFC5305], the   bandwidth advertisements defined in this document MUST be encoded as   IEEE floating-point values.  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.  SeeSection 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.Previdi, et al.              Standards Track                    [Page 5]

RFC 7810               IS-IS TE Metric Extensions               May 20164.  Sub-TLV Details4.1.  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 one (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: The A bit 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 clear,   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 sec), then the   delay is at least that value and may be larger.Previdi, et al.              Standards Track                    [Page 6]

RFC 7810               IS-IS TE Metric Extensions               May 20164.2.  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 one   (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 clear, 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.   It is possible for the Min and Max delay to be the same value.Previdi, et al.              Standards Track                    [Page 7]

RFC 7810               IS-IS TE Metric Extensions               May 2016   When the delay value (Min or Max) is set to the maximum value   16,777,215 (16.777215 sec), 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 one (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 sec), then the delay is at   least that value and may be larger.Previdi, et al.              Standards Track                    [Page 8]

RFC 7810               IS-IS TE Metric Extensions               May 20164.4.  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   one (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: The A bit 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 clear,   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 assumption   being that precision is more important on high-speed links than the   ability to advertise loss rates greater than this, and that 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.Previdi, et al.              Standards Track                    [Page 9]

RFC 7810               IS-IS TE Metric Extensions               May 20164.5.  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    |  RESERVED     |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                          Residual Bandwidth                   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   where:   Type: 37   Length: 4   RESERVED: This field is reserved for future use.  It MUST be set to 0   when sent and MUST be ignored when received.   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].  Residual bandwidth 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).Previdi, et al.              Standards Track                   [Page 10]

RFC 7810               IS-IS TE Metric Extensions               May 20164.6.  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    |  RESERVED     |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                      Available Bandwidth                      |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                 Figure 5   where:   Type: 38   Length: 4   RESERVED: This field is reserved for future use.  It MUST be set to 0   when sent and MUST be ignored when received.   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   (seeSection 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 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.Previdi, et al.              Standards Track                   [Page 11]

RFC 7810               IS-IS TE Metric Extensions               May 20164.7.  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    |  RESERVED     |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                     Utilized Bandwidth                        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                 Figure 6   where:   Type: 39   Length: 4   RESERVED: This field is reserved for future use.  It MUST be set to 0   when sent and MUST be ignored when received.   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 min/max delay and   residual bandwidth) MUST represent an average over a period or be   obtained by a filter that is reasonably representative of an average.   For example, a rolling average is one such filter.   Min and max 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 min and max value representative of   the interval, with compensation for outliers.Previdi, et al.              Standards Track                   [Page 12]

RFC 7810               IS-IS TE Metric Extensions               May 2016   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 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 an       advertisement interval(s) to permit fail back.   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 they are refreshed.   Only the accelerated advertisement threshold mechanism described inSection 5 may shorten the re-advertisement interval.  All suppression   and re-advertisement interval backoff timer features SHOULD be   configurable.Previdi, et al.              Standards Track                   [Page 13]

RFC 7810               IS-IS TE Metric Extensions               May 20167.  Network Stability and Announcement Periodicity   Sections5 and6 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 1 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.Previdi, et al.              Standards Track                   [Page 14]

RFC 7810               IS-IS TE Metric Extensions               May 201611.  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.  Implementation   SHOULD follow the described guidelines to mitigate the instability   risk.   [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 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   result in a man-in-the-middle attacker delaying real-time data to a   given site or destination, which could negatively affect the value of   the data for that site or destination.  The use of Link State PDU   cryptographic authentication allows mitigation the risk of man-in-   the-middle attack.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 BandwidthPrevidi, et al.              Standards Track                   [Page 15]

RFC 7810               IS-IS TE Metric Extensions               May 201613.  References13.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://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,              <http://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,              <http://www.rfc-editor.org/info/rfc5120>.   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic              Authentication",RFC 5304, DOI 10.17487/RFC5304, October              2008, <http://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, <http://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, <http://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, <http://www.rfc-editor.org/info/rfc6119>.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,              <http://www.rfc-editor.org/info/rfc3209>.Previdi, et al.              Standards Track                   [Page 16]

RFC 7810               IS-IS TE Metric Extensions               May 2016   [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,              <http://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,              <http://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,              <http://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,              <http://www.rfc-editor.org/info/rfc7285>.Acknowledgements   The authors would like to recognize Ayman Soliman, Nabil Bitar, David   McDysan, Les Ginsberg, Edward Crabbe, Don Fedyk, Hannes Gredler, Uma   Chunduri, Alvaro Retana, Brian Weis, and Barry Leiba for their   contribution and review of this document.   The authors also recognize Curtis Villamizar for significant comments   and direct content collaboration.Contributors   The following people contributed substantially to the content of this   document and should be considered co-authors:   Alia Atlas   Juniper Networks   United States   Email: akatlas@juniper.net   Clarence Filsfils   Cisco Systems Inc.   Belgium   Email: cfilsfil@cisco.comPrevidi, et al.              Standards Track                   [Page 17]

RFC 7810               IS-IS TE Metric Extensions               May 2016Authors' Addresses   Stefano Previdi (editor)   Cisco Systems, Inc.   Via Del Serafico 200   Rome  00191   Italy   Email: sprevidi@cisco.com   Spencer Giacalone   Microsoft   Email: spencer.giacalone@gmail.com   Dave Ward   Cisco Systems, Inc.   3700 Cisco Way   San Jose, CA  95134   United States   Email: wardd@cisco.com   John Drake   Juniper Networks   1194 N. Mathilda Ave.   Sunnyvale, CA  94089   United States   Email: jdrake@juniper.net   Qin Wu   Huawei   101 Software Avenue, Yuhua District   Nanjing, Jiangsu  210012   China   Email: sunseawq@huawei.comPrevidi, et al.              Standards Track                   [Page 18]