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]
