Internet DRAFT - draft-xu-lsr-flex-algo-link-loss
draft-xu-lsr-flex-algo-link-loss
Network Working Group G. Xu
Internet-Draft Y. Wang
Intended status: Standards Track Huawei
Expires: 15 April 2024 13 October 2023
IGP Flexible Algorithm with Link Loss
draft-xu-lsr-flex-algo-link-loss-00
Abstract
IGP Flexible Algorithms allow IGPs to compute constraint-based paths.
Since link loss plays an important role in network evaluation, links
with high packet loss rate should be bypassed during forwarding.
This draft proposes a path computation method based on a link loss
constraint to prune unsatisfied links in Flexible Algorithms.
Requirements Language
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 in BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 15 April 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Exclude Maximum Link Loss Sub-TLV . . . . . . . . . . . . . . 3
2.1. IS-IS Exclude Maximum Link Loss Sub-TLV . . . . . . . . . 3
2.2. OSPF Exclude Maximum Link Loss Sub-TLV . . . . . . . . . 4
3. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4.1. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition
Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition
Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Link packet loss rate (link loss) is a measure of the percentage of
data packets that are lost during transmission over a network. It is
an important performance metric that directly impacts the quality of
service, network congestion, security, and overall network
efficiency. Ensuring a low packet loss rate is essential for
maintaining efficient and secure network operations. Consequently,
It is necessary to avoid passing through links with a high packet
loss rate during forwarding.
The link loss is advertised by the Unidirectional Link Loss Sub-TLV
defined in [RFC8570] and [RFC7471], which describes the loss (as a
packet percentage) between two directly connected IS-IS neighbors.
This Sub-TLV is carried in the Application-Specific Link Attributes
Sub-TLV advertised by IS-IS [RFC9479] or OSPF [RFC9492].
IGP Flexible Algorithms allow IGPs to compute constraint-based paths
in [RFC9350]. Current path computation methods are based on
calculating the minimum cost of the path from the source to the
destination. Flex-Algorithm has already supported path computation
with the IGP cost, the minimum link delay and the traffic-engineering
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metric. [I-D.ietf-lsr-flex-algo-bw-con] defines a family of generic
metrics (e.g. bandwidth based metric type) and bandwidth related
constraints to support path computation based on bandwidth. However,
current calculation types and metric types cannot support path
computation based on link loss, since the cost of the path should be
defined as the maximum/minimum value among all passing links.
To overcome the above issue, there are two solutions. First, new
operators like minimum value operator can be defined, which works as
a step function. When the link loss exceeds a threshold, the cost of
the link is set to the maximum. Second, new Flexible Algorithm
Definition (FAD) constraints can be defined to exclude links that do
not meet the link loss requirements during path calculation. The
second method is specifically demonstrated in this draft. The
general ideas are as below: 1.The link loss is used as a link
constraint for path computation. That is, the link whose loss rate
is greater than the specified value is excluded. 2.Metric-type
remains unchanged: igp, te, and delay.
With a new FAD constraint Sub-TLV advertised by IGP, links with low
packet loss rate will be selected for path computation. The new
Exclude Maximum Link Loss Sub-TLVs are defined in Section 2. The
Flex-Algorithm calculation method based on link loss is presented in
Section 3.
2. Exclude Maximum Link Loss Sub-TLV
To guarantee loop free forwarding, all routers that participate in a
Flex-Algorithm MUST agree on the FAD. Selected nodes within the IGP
domain MUST advertise FADs as described in Sections 5, 6, and 7 of
[RFC9350].
A new Exclude Link Loss Constraint Sub-TLV is proposed to spcify the
upper limit of the link loss. When this Sub-TLV is carried in a FAD
TLV, all links with packet loss rate larger than the defined maximum
link loss value will be excluded from the Flex-Algorithm topology.
2.1. IS-IS Exclude Maximum Link Loss Sub-TLV
IS-IS Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a
sub-TLV of the IS-IS FAD sub-TLV. It has the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max Link Loss |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IS-IS FAEML Sub-TLV
Type: 252
Length: 3 octets
Max 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.
Therefore, measured values that are larger than the field maximum
SHOULD be encoded as the maximum value.
The FAEML sub-TLV MUST appear at most once in the FAD Sub-TLV. If it
appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the
receiver.
The maximum link loss advertised in FAEML Sub-TLV MUST be compared
with the link loss advertised in Sub-Sub-TLV 36 [RFC8570] of ASLA
Sub- TLV [RFC9479]. If L-Flag is set in the ASLA sub-TLV, the
maximum link loss advertised in FAEML sub-TLV MUST be compared with
the link loss advertised by the sub-TLV 36 of the TLV
22/222/23/223/141 [RFC5305] as defined in [RFC9479] Section 4.2.
If the link loss is larger than the maximum link loss advertised in
FAEML sub-TLV, the link MUST be excluded from the Flex-Algorithm
topology. If a link does not have the link loss advertised but the
FAD contains the FAEML sub-TLV, then it MUST NOT be excluded from the
Flex-Algorithm topology.
2.2. OSPF Exclude Maximum Link Loss Sub-TLV
OSPF Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a
sub-TLV of the OSPF FAD sub-TLV. It has the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max Link Loss |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: OSPF FAEML Sub-TLV
Type: 252
Length: 3 octets
Max 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.
Therefore, measured values that are larger than the field maximum
SHOULD be encoded as the maximum value.
The FAEML sub-TLV MUST appear at most once in the FAD Sub-TLV. If it
appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the
receiver.
The maximum link loss advertised in FAEML Sub-TLV MUST be compared
with the link loss advertised in Sub-Sub-TLV 30 [RFC7471] of ASLA
Sub- TLV [RFC9492]. The ASLA Sub-TLV is advertised in Extended Link
Opaque LSAs [RFC7684] for OSPFv2 and E-Router-LSAs [RFC8362] for
OSPFv3.
If the link loss is larger than the maximum link loss advertised in
FAEML sub-TLV, the link MUST be excluded from the Flex-Algorithm
topology. If a link does not have the link loss advertised but the
FAD contains the FAEML sub-TLV, then it MUST NOT be excluded from the
Flex-Algorithm topology.
3. Calculation of Flexible Algorithm Paths
A new rule is added to the rules used to prune links from the
topology during the Flex-Algorithm computation in Section 13 of
[RFC9350].
Check if any exclude FAEML rule is part of the Flex-Algorithm
definition. If such exclude rule exists and the link has link loss
advertised, check if the link satisfies the FAEML rule. If the link
does not satisfy the FAEML rule, the link MUST be pruned from the
computation.
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4. IANA Considerations
4.1. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Type: 252(TBA)
Description: IS-IS Exclude Maximum Link Loss Sub-TLV
Reference: This document Section 2.1
4.2. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Type: 252(TBA)
Description: OSPF Exclude Maximum Link Loss Sub-TLV
Reference: This document Section 2.2
5. References
5.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
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[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
[RFC9479] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS Application-Specific Link Attributes",
RFC 9479, DOI 10.17487/RFC9479, October 2023,
<https://www.rfc-editor.org/info/rfc9479>.
[RFC9492] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
J., and J. Drake, "OSPF Application-Specific Link
Attributes", RFC 9492, DOI 10.17487/RFC9492, October 2023,
<https://www.rfc-editor.org/info/rfc9492>.
5.2. Informative References
[I-D.ietf-lsr-flex-algo-bw-con]
Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak,
P., and T. Li, "Flexible Algorithms: Bandwidth, Delay,
Metrics and Constraints", Work in Progress, Internet-
Draft, draft-ietf-lsr-flex-algo-bw-con-07, 26 September
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
lsr-flex-algo-bw-con-07>.
[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>.
[RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/info/rfc8570>.
Authors' Addresses
Guoqi Xu
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: xuguoqi@huawei.com
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Yifan Wang
Huawei
Huawei Bld., No. 156 Beiqing Rd.
Beijing
100095
China
Email: wangyifan82@huawei.com
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