SPRING S. Hegde
Internet-Draft W. Britto
Intended status: Standards Track R. Shetty
Expires: August 26, 2021 Juniper Networks Inc.
B. Decraene
Orange
February 22, 2021
Flexible Algorithms Bandwidth Constraints
draft-hegde-lsr-flex-algo-bw-con-00
Abstract
Many networks configure the link metric relative to the link
capacity. High bandwidth traffic gets routed as per the link
capacity. Flexible algorithms provides mechanisms to create
constraint based paths in IGP. This draft documents a set of
bandwidth related constraints to be used 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 RFC 2119 [RFC2119].
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
Task Force (IETF). Note that other groups may also distribute
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 26, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Bandwidth Metric adevertisement . . . . . . . . . . . . . . . 3
2.1. ISIS Bandwidth Metric sub-TLV . . . . . . . . . . . . . . 3
2.2. OSPF Bandwidth Metric sub-TLV . . . . . . . . . . . . . . 4
3. FAD constraint sub-TLVs . . . . . . . . . . . . . . . . . . . 5
3.1. ISIS FAD constraint sub-TLVs . . . . . . . . . . . . . . 6
3.1.1. ISIS Exclude Minimum Bandwidth sub-TLV . . . . . . . 6
3.1.2. ISIS Exclude Maximum Delay sub-TLV . . . . . . . . . 6
3.2. OSPF FAD constraint sub-TLVs . . . . . . . . . . . . . . 7
3.2.1. OSPF Exclude Minimum Bandwidth sub-TLV . . . . . . . 7
3.2.2. OSPF Exclude Maximum Delay sub-TLV . . . . . . . . . 8
4. Automatic metric calculation . . . . . . . . . . . . . . . . 9
4.1. Simple mode . . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Interface group mode . . . . . . . . . . . . . . . . . . 10
4.3. ISIS FAD constraint sub-TLVs for automatic metric
calculation . . . . . . . . . . . . . . . . . . . . . . . 10
4.3.1. Reference Bandwidth sub-TLV . . . . . . . . . . . . . 10
4.3.2. Threshold metric sub-TLV . . . . . . . . . . . . . . 12
4.4. OSPF FAD constraint sub-TLVs for automatic metric
calculation . . . . . . . . . . . . . . . . . . . . . . . 14
4.4.1. Reference Bandwidth sub-TLV . . . . . . . . . . . . . 14
4.4.2. Threshold metric sub-TLV . . . . . . . . . . . . . . 16
5. Backward Compatibility . . . . . . . . . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7.1. IGP Metric-Type Registry . . . . . . . . . . . . . . . . 17
7.2. ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-
TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.3. OSPF Sub-TLVs for Flexible Algorithm Definition Sub-TLV . 18
7.4. Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 . . . . . 18
7.5. Sub-sub-TLV Codepoints for Application-Specific Link
Attributes . . . . . . . . . . . . . . . . . . . . . . . 18
7.6. OSPFv2 Extended Link TLV Sub-TLVs . . . . . . . . . . . . 19
7.7. Types for sub-TLVs of TE Link TLV (Value 2) . . . . . . . 19
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
High bandwidth traffic such as residential internet traffic and
machine to machine elephant flows benefit from using high capacily
links for the traffic. Many network operators define link metric
relative to the link capacity. It may be useful to exclude the high
bandwidth traffic from utilizing links below certain capacity. A
flex-algo [I-D.ietf-lsr-flex-algo] is defined as a set of parameters
consisting of calculation-type, metric-type and a set of constraints.
It is very convenient to define a flex-algo that uses bandwidth based
metric-type which can be used for carrying high bandwidth traffic.In
this regard, it's useful to define additional metric-type and
additional bandwidth related constraints to simplify the operations.
This document specifies a new metric-type to be used in flex-algo
described in section Section 2. Additional Flexible Algorithm
Definition (FAD) constraints defined in section Section 3. Section 4
defines mechanisms to automatically calculate metric based on
reference bandwidth and actual link bandwidth.
2. Bandwidth Metric adevertisement
ISIS and OSPF advertise link metric in their respective link
information. Multiple types of metric are supported, IGP cost, te-
metric defined in [RFC5305] and [RFC3630] and delay metric defined in
[RFC8570] and [RFC7471]. A brownfield network might have deployed
legacy transport mechanisms using igp-cost and te-metric which
continue to run during migration period. In this brownfield network
if the operator wants to introduce two Flex-Algos, one for delay
metric and another for bandwidth metric, a new metric-type to carry
bandwidth related metric, would be needed. The IGP cost and te-
metric may be already used by legacy applications and may not be
available to carry link bandwidth based metric. This document
defines a new metric called bandwidth metric. ISIS and OSPF will
advertise this new type of metric in their link information. This
document also defines a new metric-type called "bandwidth metric" in
the FAD sub-TLV.
2.1. ISIS Bandwidth Metric sub-TLV
The ISIS Bandwidth Metric sub-TLV specifies the link metric based on
link bandwidth. Typically, this metric is assigned by a network
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administrator. The bandwidth metric sub-TLV is advertised in below
TLVs
TLV-22 (Extended IS reachability) [RFC5305]
TLV-222 (MT-ISN) [RFC5120]
TLV-23 (IS Neighbor Attribute) [RFC5311]
TLV-223 (MT IS Neighbor Attribute) [RFC5311]
TLV-141 (inter-AS reachability information) [RFC5316]
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type : TBD (To be assigned by IANA)
Length: 5 octets
Value : metric value range (1 - 4,261,412,864)
Figure 1: ISIS bandwidth metric sub-TLV
The bandwidth metric sub-TLV MUST be advertised only once. If there
are multiple bandwidth metric sub-TLVs in one or more received
LSPDUs, the first one MUST be used and the subsequesnt ones MUST be
ignored.
2.2. OSPF Bandwidth Metric sub-TLV
The Bandwidth Metric sub-TLV specifies the link metric based on link
bandwidth. Typically, this metric is assigned by a network
administrator. The bandwidth metric sub-TLV is a sub-TLV of the OSPF
Link TLV and advertised in OSPF extended Link LSA [RFC7684]. The
Bandwidth Metric sub-TLV is TLV type TBD (IANA), and is four octets
in length.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type : TBD (To be assigned by IANA)
Length: 4 octets
Value : metric value (1- 4,294,967,296)
Figure 2: OSPF bandwidth metric sub-TLV
The bandwidth metric sub-TLV MUST be advertised only once. If there
are multiple bandwidth metric sub-TLVs in a receieved Link TLV, the
first one MUST be used and the subsequent ones MUST be ignored.
3. FAD constraint sub-TLVs
It is useful to exclude Links having capacity lower than a minimum
value from the flex-algo topology that is designed to carry high
bandwidth traffic. This can be achieved by associating link affinity
to the lower capacity links and advertise exclude link constraint in
the FAD for that link affinity. This works well where the link
capacity is constant. When a L3 link is collection of L2 links (LAG/
L2 Bundle) , the link bandwidth varies based on the constituent link
going up and down. The operator has to constantly monitor the link
capacity and assign appropriate link affinity on link capacity
changes beyond minimum value. In certain cases, the minimum link
bandwidth required may change based on the applications that use the
high bandwidth Flex-Algo. This document proposes a new exclude
minimum bandwidth constraint. When this constraint is advertised in
a FAD, based on the advertised link bandwidth, the link will be
pruned from the flex-algo topology if its below the FAD advertised
Minimum bandwidth value.
Similarly, exclude maximum link delay constraint is also defined in
this document. Links may have the link delay measured dynamically
and advertised in delay metric in IGP. For usecases that deploy low
latency flex-algo, may want to exclude links that have delay more
than a defined threshold.
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3.1. ISIS FAD constraint sub-TLVs
3.1.1. ISIS Exclude Minimum Bandwidth sub-TLV
ISIS Flex-algo Exclude Minimum Bandwidth sub-TLV (FAEMB) is a sub-TLV
of the ISIS FAD sub-TLV. It 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 1
Length: 4 octets.
Min Bandwidth: link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Figure 3: ISIS FAEMB sub-TLV
The FAEMB sub-TLV MUST appear only once in the FAD sub-TLV. If it
appears more than once, the ISIS FAD Sub-TLV MUST be ignored by the
receiver. The total link bandwidth as advertised by the sub-TLV 9 of
the TLV 22/222/23/223/141 is compared against the Min bandwidth
advertised in FAEMB sub-TLV. If the link bandwidth is lower, the
link is excluded from the Flex-algo topology of the corresponding
Flex-algo which advertised the FAEMB sub-TLV. If a link does not
have the link bandwidth advertised but the FAD contains this sub-TLV,
then that link MUST be excluded from the topology.
3.1.2. ISIS Exclude Maximum Delay sub-TLV
ISIS Flex-algo Exclude Maximum Delay sub-TLV (FAEMD) is a sub-TLV of
the ISIS 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 delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 3 octets
Max link delay: Maximum link delay in microseconds
Figure 4: ISIS FAEMD sub-TLV
The FAEMD sub-TLV MUST appear only once in the FAD sub-TLV. If it
appears more than once, the ISIS FAD Sub-TLV MUST be ignored by the
receiver. The link delay [RFC8570].as advertised by the sub-TLV 33
of the TLV 22/222/23/223/141 is compared against the Max link delay
advertised in FAEMD sub-TLV. If the link delay value is higher, the
link is excluded from the Flex-algo topology of the corresponding
Flex-algo which advertised the FAEMD sub-TLV. If a link does not
have the link delay advertised but the FAD contains this sub-TLV,
then that link MUST be excluded from the topology.
3.2. OSPF FAD constraint sub-TLVs
3.2.1. OSPF Exclude Minimum Bandwidth sub-TLV
OSPF Flex-algo Bandwidth Exclusion sub-TLV (FAEMB) is a sub-TLV of
the OSPF FAD 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 4 octets.
Min Bandwidth: link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Figure 5: OSPF FAEMB sub-TLV
The FAEMB sub-TLV MUST appear only once in the FAD sub-TLV. If it
appears more than once, the OSPF FAD TLV MUST be ignored by the
receiver. The total link bandwidth as advertised by the sub-TLV 6 of
the Extended Link TLV of Extended Link Opaque LSA [RFC 7684] is
compared against the Min bandwidth advertised in FAEMB sub-TLV. If
the link bandwidth is lesser, the link is excluded from the Flex-algo
topology of the corresponding Flex-algo which advertised the FAEMB
sub-TLV. If a link does not have the link bandwidth advertised but
the FAD contains this sub-TLV, then that link MUST be excluded from
the topology.
3.2.2. OSPF Exclude Maximum Delay sub-TLV
OSPF Flex-algo Exclude Maximum Delay sub-TLV (FAEMD) is a sub-TLV of
the OSPF FAD 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 delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 4 octets
Max link delay: Maximum link delay in microseconds
Figure 6: OSPF FAEMD sub-TLV
The FAEMD sub-TLV MUST appear only once in the OSPF FAD TLV. If it
appears more than once, the OSPF FAD TLV MUST be ignored by the
receiver. The link delay as advertised by the sub-TLV 27 of the
Extended Link TLV of Extended link opaque LSA [RFC 7684] is compared
against the Max delay advertised in FAEMD sub-TLV. If the link delay
value is higher, the link is excluded from the Flex-algo topology of
the corresponding Flex-algo which advertised the FAEMD sub-TLV. If a
link does not have the link delay advertised but the FAD contains
this sub-TLV, then that link MUST be excluded from the topology.
4. Automatic metric calculation
Networks which are designed to be highly regular and follow uniform
metric assignment may want to further simplify the operations by
automatically calculating the metric based on the reference bandwidth
or a staircase metric assignment based on bandwidth thresholds.
Based on the advertised rules, every node automatically calculates
the link metric of the links in the network before running SPF
algorithm. Based on the delay in receiving the link bandwidth
changes, there may be possibility of micro-loops which is no
different from IGP susceptibility to micro-loops during metric
change. The micro-loop avoidance procedures described in
[I-D.bashandy-rtgwg-segment-routing-uloop] can be used to avoid
micro-loops when the automatic metric calculation is deployed.
4.1. Simple mode
In simple mode, the link bandwidth of a single Layer 3 link is used.
Two ways of automatic metric calculation is supported.
1. Based on reference bandwidth
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2. Staircase metric values based on bandwidth thresholds
4.2. Interface group mode
Simple mode of metric calculation may not work well when there are
multiple parallel layer 3 interfaces between two nodes.
A------B======C=======D
| |
------E-------
Figure 7: Parallel interfaces
In the above diagram, there are two parallel links between B->C and
C->D. Lets assume the link bandwidth is uniform 10Gbps on all links.
When Simple mode of metric derivation is used,the metric is derived
as 10 on all links. Traffic will be load balanced beween B-> C->D
and B->E->D. Since the bandwidth is higher B->C->D path, the
requirement is t be able to assign smaller metric based on cumulative
metric for the parallel links.
In the interface group mode, every node identifies the set of
parallel links betweena pair of nodes based on IGP link
advertisements and considers cumulative bandwidth of the parallel
links while arriving at the metric for the link. Two ways of
automatic metric calculation is supported for interface group mode as
well.
1. Based on reference bandwidth
2. Staircase metric values based on bandwidth thresholds
The cumulative metric of the parallel link is used and based on
reference bandwidth or staircase metric assignment method, metric
value is derived. The derived metric is assigned to each of the
parallel link between nodes. Interface group mode is useful for
deployments that do not use L2 bundles.
4.3. ISIS FAD constraint sub-TLVs for automatic metric calculation
4.3.1. Reference Bandwidth sub-TLV
The Flexible Algorithm Definition Reference Bandwidth Sub-TLV (FADRB
Sub-TLV) is a Sub-TLV of the ISIS 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 | Reserved |S| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reference Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Roundoff BW. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 10 octets.
Reference Bandwidth: link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Roundoff BW: link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S| | | |
+-+-+-+-+-+-+-+-+
S-flag: when set, interface group Mode MUST be used to derive total link bandwidth.
Metric calculation: (Reference_bandwidth) /
(Total_link_bandwidth -
(Mod of(Total_link_bandwidth,roundoff_bw)))
Round-off BW value is used to make sure the the metric
does not change when there is smaller
change in the link bandwidth.
Figure 8: ISIS FADRB sub-TLV
The ISIS FADRB Sub-TLV MUST NOT appear more then once in an ISIS FAD
sub-TLV. If it appears more then once, the ISIS FAD sub-TLV MUST be
ignored by the receiver.
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4.3.2. Threshold metric sub-TLV
The Flexible Algorithm Definition Threshold Bandwidth Sub-TLV (FADTB
Sub-TLV) is a Sub-TLV of the ISIS 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 | Reserved |S| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Bandwidth 1 Min. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Bandwidth 1 Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold metric 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Bandwidth n Min. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Bandwidth n Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold metric n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 2 + n*12 octets.Here n is equal to Number of Threshold Bandwidth sets specified.
Flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S| | | |
+-+-+-+-+-+-+-+-+
S-flag: when set, interface group Mode MUST be used to derive total link bandwidth.
Staircase bandwidth threshold and associated metric values.
Threshold Bandwidth 1 Min.: Minimum link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Threshold Bandwidth 1 Max.:Maximum link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Threshold metric 1 : metric value range (1 - 4,294,967,296)
When the computed link bandwidth is in the range specified by
Min and Max threshold bandwidth values,
the corresponding metric value is assigned to the link during SPF calculation.
Figure 9: ISIS FADTB sub-TLV
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The ISIS FADTB Sub-TLV MUST NOT appear more then once in an ISIS FAD
sub-TLV. If it appears more then once, the ISIS FAD sub-TLV MUST be
ignored by the receiver.
4.4. OSPF FAD constraint sub-TLVs for automatic metric calculation
4.4.1. Reference Bandwidth sub-TLV
The Flexible Algorithm Definition Reference Bandwidth Sub-TLV (FADRB
Sub-TLV) is a Sub-TLV of the OSPF FAD 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |S| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reference Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Roundoff BW. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 10 octets.
Reference Bandwidth: link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Roundoff BW: link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S| | | |
+-+-+-+-+-+-+-+-+
S-flag: when set, interface group Mode MUST be used
to derive total link bandwidth.
Metric calculation: (Reference_bandwidth) /
(Total_link_bandwidth -
(Mod of(Total_link_bandwidth,roundoff_bw)))
Round-off BW value is used to make sure the the
metric does not change when there is smaller
change in the link bandwidth.
Figure 10: OSPF FADRB sub-TLV
The OSPF FADRB Sub-TLV MUST NOT appear more then once in an OSPF FAD
TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored
by the receiver.
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4.4.2. Threshold metric sub-TLV
The Flexible Algorithm Definition Threshold Bandwidth Sub-TLV (FADTB
Sub-TLV) is a Sub-TLV of the OSPF FAD TLV. It 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |S| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Bandwidth 1 Min. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Bandwidth 1 Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold metric 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Bandwidth n Min. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Bandwidth n Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold metric n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 2 + n*12 octets.Here n is equal to Number of Threshold Bandwidth specified.
Flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S| | | |
+-+-+-+-+-+-+-+-+
S-flag: when set, interface group Mode MUST be used to derive total link bandwidth.
Stircase bandwidth threshold and associated metric values.
Threshold Bandwidth 1 Min.: Minimum link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
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Threshold Bandwidth 1 Max.:Maximum link bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Threshold metric 1 : metric value range (1 - 4,294,967,296)
When the computed link bandwidth is in the range specified by
Min and Max threshold bandwidth values,
the corresponding metric value is assigned to the link during SPF calculation.
Figure 11: OSPF FADTB sub-TLV
The OSPF FADTB Sub-TLV MUST NOT appear more then once in an OSPF FAD
TLV. If it appears more then once, the OSPF FAD TLV MUST be ignored
by the receiver.
5. Backward Compatibility
6. Security Considerations
TBD
7. IANA Considerations
7.1. IGP Metric-Type Registry
Type: Suggested 3 (TBA)
Description: Bandwidth metric
Reference: This document
7.2. ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Type: Suggested 6 (TBA)
Description: ISIS Exclude Minimum Bandwidth sub-TLV
Reference: This document Section 3.1.1
Type: Suggested 7 (TBA)
Description: ISIS Exclude Maximum Delay sub-TLV
Reference: This document Section 3.1.2
Type: Suggested 8 (TBA)
Description: ISIS Reference Bandwidth sub-TLV
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Reference: This document Section 4.3.1
Type: Suggested 9 (TBA)
Description: ISIS Threshold metric sub-TLV
Reference: This document Section 4.3.2
7.3. OSPF Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Type: Suggested 6 (TBA)
Description: OSPF Exclude Minimum Bandwidth sub-TLV
Reference: This document Section 3.2.1
Type: Suggested 7 (TBA)
Description: OSPF Exclude Maximum Delay sub-TLV
Reference: This document Section 3.2.2
Type: Suggested 8 (TBA)
Description: OSPF Reference Bandwidth sub-TLV
Reference: This document Section 4.4.1
Type: Suggested 9 (TBA)
Description: OSPF Threshold metric sub-TLV
Reference: This document Section 4.4.2
7.4. Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223
Type: Suggested 45 (TBA)
Description: Bandwidth metric
Reference: This document Section 2.1
7.5. Sub-sub-TLV Codepoints for Application-Specific Link Attributes
Type: Suggested 45 (TBA)
Description: Bandwidth metric
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Reference: This document Section 2.1
7.6. OSPFv2 Extended Link TLV Sub-TLVs
Type: Suggested 45 (TBA)
Description: Bandwidth metric
Reference: This document Section 2.2
7.7. Types for sub-TLVs of TE Link TLV (Value 2)
Type: Suggested 45 (TBA)
Description: Bandwidth metric
Reference: This document Section 2.2
8. Acknowledgements
Many thanks to Chris Bowers, Krzysztof Szarcowitz, Julian Lucek, Ram
Santhanakrishnan for discussions and inputs.
9. Contributors
1. Salih K A
Juniper Networks
salih@juniper.net
10. References
10.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<https://www.rfc-editor.org/info/rfc3630>.
[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>.
10.2. Informative References
[I-D.bashandy-rtgwg-segment-routing-uloop]
Bashandy, A., Filsfils, C., Litkowski, S., Decraene, B.,
Francois, P., and P. Psenak, "Loop avoidance using Segment
Routing", draft-bashandy-rtgwg-segment-routing-uloop-10
(work in progress), December 2020.
[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>.
[RFC5311] McPherson, D., Ed., Ginsberg, L., Previdi, S., and M.
Shand, "Simplified Extension of Link State PDU (LSP) Space
for IS-IS", RFC 5311, DOI 10.17487/RFC5311, February 2009,
<https://www.rfc-editor.org/info/rfc5311>.
[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>.
[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>.
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Authors' Addresses
Shraddha Hegde
Juniper Networks Inc.
Exora Business Park
Bangalore, KA 560103
India
Email: shraddha@juniper.net
William Britto A J
Juniper Networks Inc.
Email: bwilliam@juniper.net
Rajesh Shetty
Juniper Networks Inc.
Email: mrajesh@juniper.net
Bruno Decraene
Orange
Email: bruno.decraene@orange.com
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