LSR Working Group Yao. Liu
Internet-Draft Shaofu. Peng
Intended status: Standards Track ZTE Corp.
Expires: October 24, 2021 April 22, 2021
Flexible Algorithm with Bandwidth Constrains
draft-lp-lsr-fa-bandwidth-00
Abstract
This document proposes extensions for IGP to allow the computation
based on bandwidth constraints together with the existing metric in
Flexible Algorithm.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
3. ISIS bandwidth constraint Sub-TLV of ISIS FAD Sub-TLV . . . 3
4. OSPF bandwidth constraint Sub-TLV of ISIS FAD Sub-TLV . . . 3
5. Calculation of Flex Algorithm Paths . . . . . . . . . . . . . 4
5.1. Calculation . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Illustration . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.1. ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-
TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. OSPF Sub-Sub-TLVs for Flexible Algorithm Definition Sub-
TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
[I-D.ietf-lsr-flex-algo] defines the Flex-Algorithm as a set of
parameters consisting of calculation-type, metric-type and a set of
constraints. The metric includes igp-metric, te-metric, delay-
metric, and etc.
While the calculation of a path based on metrics is accumulative,
e.g, the path calculated based on the delay-metric is that with the
smallest sum of the metrics of each link. The bandwidth of a path
depends on the link with the smallest bandwidth among the links that
comprise the path.
It's more appropriate that the bandwidth acts as a constraint instead
of a metric in the path computation.
This document proposes extensions for IGP to allow the computation
based on bandwidth constraints together with the existing metric in
FLex-Algo.
2. Conventions used in this document
2.1. 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
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. ISIS bandwidth constraint Sub-TLV of ISIS FAD Sub-TLV
This document defines the ISIS bandwidth constraint Sub-TLV. It is a
Sub-TLV of the ISIS FAD Sub-TLV [I-D.ietf-lsr-flex-algo] and has the
following format:
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 | BW-Con Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ISIS bandwidth constraint Sub-TLV
where:
o Type: TBA
o Length: 1 octets
o BW-Con Type: 1 octets of bandwidth constraint information.
The BW-Con Type has the following values:
1: Choose the link with Maximum Link Bandwidth ( MLB defined in
[RFC5305] ).
2: Choose the link with maximum Unidirectional Available Bandwidth (
UAB defined in [RFC8570] ).
3: Choose the link with the lowest bandwidth utilization rate.
The ISIS bandwidth constraint Sub-TLV MUST NOT appear more than once
in an ISIS FAD Sub-TLV. If it appears more than once, the ISIS FAD
Sub-TLV MUST be ignored by the receiver.
4. OSPF bandwidth constraint Sub-TLV of ISIS FAD Sub-TLV
This document defines the OSPF bandwidth constraint Sub-TLV. It is a
Sub-TLV of the OSPF FAD Sub-TLV [I-D.ietf-lsr-flex-algo] and 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BW-Con Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: OSPF bandwidth constraint Sub-TLV
where:
o Type: TBA
o Length: 1 octets
o BW-Con Type: 1 octets of bandwidth constraint information.
The BW-Con Type has the following values:
1: Choose the link with Maximum Bandwidth ( MB defined in [RFC3630]
).
2: Choose the link with maximum Unidirectional Available Bandwidth (
UAB defined in [RFC7471] ).
3: Choose the link with the lowest bandwidth utilization rate.
The OSPF bandwidth constraint Sub-TLV MUST NOT appear more than once
in a OSPF FAD Sub-TLV. If it appears more than once, the OSPF FAD
Sub-TLV MUST be ignored by the receiver.
5. Calculation of Flex Algorithm Paths
Routes that don't support the bandwidth constraint Sub-TLV MUST NOT
participate in the corresponding Flex-Algo plane.
Existing rules for calculation of Flex-Algorithm paths specified in
[I-D.ietf-lsr-flex-algo] are still applicable.
As for the new bandwidth constraint, first, select the optimal
path(s) only according to the bandwidth constraint. If there are
multiple candidate paths satisfying the bandwidth constraint, then
select the best path based on the metric computation from these
candidate paths.
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5.1. Calculation
The result of IGP flex algo shortest path calculation based on
bandwidth constraints is that each participating node in flex algo
plane constructs a SPT (with itself as the root) per algorithm, which
contains all other participating nodes as destination nodes.
Step1: Assume S is the root, and other nodes are D1, D2, D3,... Dn.
Step2: Find all paths from source node S to destination node D1.
Suppose there is one or more paths, and it is recorded as path-1,
path-2,..., path-m, where m > =1.
Step3: Initializes the current root node (cur-root) to S. Take two
paths (such as path-1 and path-2) to compare to see who is more
qualified for the constraint. Note that as mentioned above, the
constraint conditions here refer to the combination of bandwidth
constraint and metric, and compare based on bandwidth constraints
firstly and then metric secondly. This can be compared in segments,
that is, from the current root node to the destination node, finding
a first crossed node which appears in two paths at the same time and
is recorded as the current branch (cur-branch) node.
Step4: Compare the path segment from the current root node to the
current branch node in the two paths to see who is more qualified for
the path. If one of the two path segments is optimal and the other
is suboptimal, it means that one of the two paths is optimal than the
other. Add the optimal path to the "winning group". Note that if
the path of the suboptimal is originally in the "winning group", the
"winning group" should be cleared firstly and then new optimal path
is added. The optimal path continues to compare with other paths,
jump to Step3.
Otherwise, if the two path fragments are both optimal, the current
root node (cur root) is updated as the current branch node. If the
current root node reaches the destination node, the comparison is
finished, and the two paths join the "winning group" to form ECMP
(equal cost multi path equivalent multipath); otherwise, continue to
find the next crossed node in the two paths as the new current branch
node, and jump to Step4.
Step5: The above result will get the shortest paths from S to D1.
Similarly, repeating Step2 for destination D2, D3,..., Dn
respectively will get the shortest path from S to D2, D3,..., Dn
respectively. Thus the shortest path tree with S as the root node in
the flex algo plane is constructed.
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5.2. Illustration
+----D----+
| |
A------B C
| |
+----E----+
Figure 3: Reference Topology
As shown in Figure 3, there're 5 nodes in the given FA plane, whose
metric type is delay metric and the bandwidth constrain is to choose
the link with the maximum total bandwidth.
The bandwidth and metric for each link is shown in Table 1.
+------+-----------+--------+
| Link | Bandwidth | Metric |
+------+-----------+--------+
| A-B | 100 | 10 |
| B-D | 5 | 2 |
| D-C | 10 | 2 |
| B-E | 10 | 1 |
| E-C | 5 | 1 |
+------+-----------+--------+
Table 1: Bandwidth and Metric
It is required to calculate the optimal path from A to C in this FA
plane.
First, select the path who has the maximum bandwidth . Since the
bandwidth of a path depends on the link with the smallest bandwidth,
the maximum bandwidth s of path A-B-D-C and A-B-E-C are both 5.
These two paths are chosen as candidate paths.
Second, compare the metric values of the candidate paths. The metric
of path A-B-E-C is smaller, so it is chosen as the best path.
6. Security Considerations
TBD
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7. IANA Considerations
7.1. ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Type: TBA
Description: bandwidth constraint Sub-TLV
Reference: This document.
7.2. OSPF Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Type: TBA
Description: bandwidth constraint Sub-TLV
Reference: This document.
8. References
8.1. Normative References
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-13 (work in progress), October 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, .
8.2. Informative References
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, .
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[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,
.
[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, .
Authors' Addresses
Liu Yao
ZTE Corp.
Email: liu.yao71@zte.com.cn
Peng Shaofu
ZTE Corp.
Email: peng.shaofu@zte.com.cn
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