Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints
draft-hegde-lsr-flex-algo-bw-con-01
The information below is for an old version of the document.
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|---|---|---|---|
| Authors | Shraddha Hegde , William Britto , Rajesh Shetty , Bruno Decraene , Peter Psenak , Tony Li | ||
| Last updated | 2021-03-08 | ||
| Replaced by | draft-ietf-lsr-flex-algo-bw-con | ||
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draft-hegde-lsr-flex-algo-bw-con-01
SPRING S. Hegde
Internet-Draft W. Britto
Intended status: Standards Track R. Shetty
Expires: September 9, 2021 Juniper Networks Inc.
B. Decraene
Orange
P. Psenak
Cisco Systems
T. Li
Arista Networks
March 8, 2021
Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints
draft-hegde-lsr-flex-algo-bw-con-01
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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 September 9, 2021.
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Copyright Notice
Copyright (c) 2021 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Bandwidth Metric Advertisement . . . . . . . . . . . . . . . 3
2.1. ISIS Bandwidth Metric sub-TLV . . . . . . . . . . . . . . 4
2.2. OSPF Bandwidth Metric sub-TLV . . . . . . . . . . . . . . 5
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 . . . . . . . . . 7
3.2. OSPF FAD constraint sub-TLVs . . . . . . . . . . . . . . 7
3.2.1. OSPF Exclude Minimum Bandwidth sub-TLV . . . . . . . 8
3.2.2. OSPF Exclude Maximum Delay sub-TLV . . . . . . . . . 8
4. Automatic Metric Calculation . . . . . . . . . . . . . . . . 9
4.1. Automatic Metric Calculation Modes . . . . . . . . . . . 10
4.1.1. Simple Mode . . . . . . . . . . . . . . . . . . . . . 10
4.1.2. Interface Group Mode . . . . . . . . . . . . . . . . 10
4.2. Automatic Metric Calculation Methods . . . . . . . . . . 10
4.2.1. Reference Bandwidth method . . . . . . . . . . . . . 11
4.2.2. Bandwidth Thresholds method . . . . . . . . . . . . . 11
4.3. ISIS FAD constraint sub-TLVs for automatic metric
calculation . . . . . . . . . . . . . . . . . . . . . . . 11
4.3.1. Reference Bandwidth sub-TLV . . . . . . . . . . . . . 11
4.3.2. Bandwidth Thresholds sub-TLV . . . . . . . . . . . . 13
4.4. OSPF FAD constraint sub-TLVs for automatic metric
calculation . . . . . . . . . . . . . . . . . . . . . . . 15
4.4.1. Reference Bandwidth sub-TLV . . . . . . . . . . . . . 15
4.4.2. Bandwidth Threshold sub-TLV . . . . . . . . . . . . . 17
5. Bandwidth metric considerations . . . . . . . . . . . . . . . 19
6. Calculation of Flex-Algorithm paths . . . . . . . . . . . . . 19
7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
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9.1. IGP Metric-Type Registry . . . . . . . . . . . . . . . . 20
9.2. ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-
TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.3. OSPF Sub-TLVs for Flexible Algorithm Definition Sub-TLV . 21
9.4. Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 . . . . . 21
9.5. Sub-sub-TLV Codepoints for Application-Specific Link
Attributes . . . . . . . . . . . . . . . . . . . . . . . 21
9.6. OSPFv2 Extended Link TLV Sub-TLVs . . . . . . . . . . . . 21
9.7. Types for sub-TLVs of TE Link TLV (Value 2) . . . . . . . 22
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
12.1. Normative References . . . . . . . . . . . . . . . . . . 22
12.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
High bandwidth traffic such as residential internet traffic and
machine to machine elephant flows benefit from using high capacity
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-Algorithm [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-Algorithm 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-
Algorithm described in section Section 2. Additional Flexible
Algorithm Definition (FAD) constraints are defined in section
Section 3. Section 4 defines mechanisms to automatically calculate
metric based on parameters defined in a FAD constraint and the
advertised Maximum Link Bandwidth of the link.
2. Bandwidth Metric Advertisement
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-Algorithms, one for delay
metric and another for bandwidth metric, a new metric-type to carry
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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
administrator. The Bandwidth Metric sub-TLV is advertised in below
TLVs/sub-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]
sub-TLV 16 (Application-Specific Link Attributes) of TLV
22/222/23/223/141 [RFC8919]
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 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 advertised for a link in one
or more received LSPDUs, the first one MUST be used and the
subsequent ones MUST be ignored.
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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 advertised in below
TLVs
sub-TLV of the OSPF Link TLV of OSPF extended Link LSA [RFC7684].
sub-TLV of TE Link TLV (2) of OSPF TE LSA [RFC3630].
sub-sub-TLV of Application-Specific Link Attributes sub-TLV [RFC
8920]
The Bandwidth Metric sub-TLV is TLV type TBD (IANA), and is four
octets in length.
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- 4,294,967,295)
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 received 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-Algorithm 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 Layer 3 link is collection of Layer 2
links (LAG/Layer 2 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 if
link capacity changes beyond minimum value. In certain cases, the
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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-Algorithm topology if the link's
advertised Maximum Link Bandwidth is 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 use cases that deploy
dynamic link delay measurement, A Flex-Algorithm may want to exclude
links that have link delay more than a defined threshold.
3.1. ISIS FAD constraint sub-TLVs
3.1.1. ISIS Exclude Minimum Bandwidth sub-TLV
ISIS Flex-Algorithm 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 Minimum bandwidth advertised in FAEMB sub-TLV MUST be
compared with Maximum Link Bandwidth advertised in sub-sub-TLV 9 of
ASLA sub-TLV [RFC 8919]. If L-Flag is set in the ASLA sub-TLV, the
Minimum bandwidth advertised in FAEMB sub-TLV MUST be compared with
Maximum Link Bandwidth as advertised by the sub-TLV 9 of the TLV
22/222/23/223/141 [RFC 5305] as defined in [RFC8919] Section 4.2. If
the Maximum Link Bandwidth is lower than the Minimum link bandwidth
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advertised in FAEMB sub-TLV, the link MUST be excluded from the Flex-
Algorithm topology. If a link does not have the Maximum Link
Bandwidth advertised but the FAD contains this sub-TLV, then that
link MUST be included in the topology and proceed to apply further
pruning rules for the link.
3.1.2. ISIS Exclude Maximum Delay sub-TLV
ISIS Flex-Algorithm Exclude Maximum Delay sub-TLV (FAEMD) 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 Maximum link delay advertised in FAEMD sub-TLV MUST be
compared with Min Unidirectional Link Delay advertised in sub-sub-TLV
34 of ASLA sub-TLV [RFC 8919]. If L-Flag is set in the ASLA sub-TLV,
the Maximum link delay advertised in FAEMD sub-TLV MUST be compared
with Min Unidirectional Link Delay as advertised by the sub-TLV 34 of
the TLV 22/222/23/223/141 [RFC 8570] as defined in [RFC8919]
Section 4.2. If the Min Unidirectional Link Delay value is higher
than the Maximum link delay advertised in FAEMD sub-TLV, the link
MUST be excluded from the Flex-Algorithm topology. If a link does
not have the Min Unidirectional Link Delay advertised but the FAD
contains this sub-TLV, then that link MUST be included in the
topology and proceed to apply further pruning rules for the link.
3.2. OSPF FAD constraint sub-TLVs
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3.2.1. OSPF Exclude Minimum Bandwidth sub-TLV
OSPF Flex-Algorithm Bandwidth Exclusion sub-TLV (FAEMB) 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 Maximum Link Bandwidth as advertised by the sub-sub-
TLV 23 of ASLA [RFC 8920] MUST be compared against the Minimum
bandwidth advertised in FAEMB sub-TLV. If the link bandwidth is
lower than the Minimum bandwidth advertised in FAEMB sub-TLV, the
link MUST be excluded from the Flex-Algorithm topology. If a link
does not have the Maximum Link Bandwidth advertised but the FAD
contains this sub-TLV, then that link MUST be included in the
topology and proceed to apply further pruning rules for the link.
3.2.2. OSPF Exclude Maximum Delay sub-TLV
OSPF Flex-Algorithm 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: 3 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 Min Unidirectional Link Delay as advertised by sub-
sub-TLV 12 of ASLA sub-TLV [RFC 8920], MUST be compared against the
Maximum delay advertised in FAEMD sub-TLV. If the Min Unidirectional
Link Delay is higher than the Maximum delay advertised in FAEMD sub-
TLV, the link MUST be excluded from the Flex-Algorithm topology. If
a link does not have the Min Unidirectional Link Delay advertised but
the FAD contains this sub-TLV, then that link MUST be included in the
topology and proceed to apply further pruning rules for the link.
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 a reference bandwidth
or a staircase metric assignment based on bandwidth thresholds. When
a FAD advertises metric-type as Bandwidth Metric and the link does
not have the Bandwidth Metric advertised, automatic metric derivation
can be used with additional FAD constraint advertisements as
described in this section. Based on the advertised rules, every node
automatically calculates the link metric of all the links in the
Flex-Algorithm before running SPF algorithm for the Flex-Alogrithm.
Based on the delay in learning the link bandwidth changes on a remote
link, 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.
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4.1. Automatic Metric Calculation Modes
4.1.1. Simple Mode
In simple mode, the Maximum Link Bandwidth of a single Layer 3 link
is used to derive the metric. This mode is more suitable for
deployments that use Layer 2 bundles for parallel links between two
nodes. This layer 3 link may consist of Layer 2 bundles. In such
cases, the bandwidth of the link may vary based on Layer 2 links
going up/down.
4.1.2. 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====F====D
| |
------E-------
Figure 7: Parallel interfaces
In the above diagram, there are two parallel links between B->C,
C->F, F->D. Let us 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 forwarded B->E->D.
Since the bandwidth is higher B->C->F->D path, the requirement is to
be able to assign smaller metric based on cumulative bandwidth of the
parallel links. Interface group mode is suitable for deployments
that do not use Layer 2 bundles.
In the interface group mode, every node MUST identify the set of
parallel links between a pair of nodes based on IGP link
advertisements and MUST consider cumulative bandwidth of the parallel
links while arriving at the metric of each link.
4.2. Automatic Metric Calculation Methods
In automatic metric calculation for simple and interface group mode,
Maximum Link Bandwidth of the links is used to derive the metric.
There are two types of automatic metric derivation methods.
1. Reference bandwidth method
2. Bandwidth thresholds method
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4.2.1. Reference Bandwidth method
In many networks, the metric is assigned relative to the link
bandwidth. The metric is derived by dividing the reference bandwidth
by the advertised Maximum Link Bandwidth. It is useful to advertise
reference bandwidth in FAD constraints to simplify operations. When
there are changes to the reference bandwidth it can be easily changed
on FAD server rather than having to change it on every node. In
order to ensure that small bandwidth changes do not change the link
metric, it is useful to define a round-off value. The link bandwidth
will be rounded-off with this value before deriving the metric. For
example,
reference bandwidth = 1000G
round off value = 20G
The derived metric is 10 for link bandwidth in the range 100G to
119G
4.2.2. Bandwidth Thresholds method
The round-off bw along with reference bandwidth approach described
above provides a uniform metric value for a range of link bandwidth.
In certain cases there may be a need to define non-proportional
metric values for the varying ranges of link bandwidth. For Example,
10G to 30G metric value is 100, 30G to 70G metric value is 50,
greater than 70G metric is 10. In order to support this, a staircase
metric based on bandwidth threshold is supported in the FAD. This
advertisement contains a set of threshold values and their associated
metric.
4.3. ISIS FAD constraint sub-TLVs for automatic metric calculation
4.3.1. Reference Bandwidth sub-TLV
This section provides FAD constraint advertisement details for the
reference bandwidth method of metric calculation as described in
Section 4.2.1. 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 |G| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reference Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Round-Off Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 14 octets.
Reference Bandwidth: Bandwidth encoded in 32 bits in IEEE floating point
format. The units are in bytes per second.
Round-Off Bandwidth: Bandwidth encoded in 32 bits in IEEE floating point
format. The units are in bytes per second.
Flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|G| | | |
+-+-+-+-+-+-+-+-+
G-flag: when set, interface group Mode MUST be used to derive total link bandwidth.
Metric calculation: (Reference_bandwidth) /
(Total_link_bandwidth -
(Modulus of(Total_link_bandwidth,Round_off_bw)))
Figure 8: ISIS FADRB sub-TLV
Round-off Bandwidth value is used to make sure the metric does not
change when there is smaller change in the link bandwidth. The ISIS
FADRB 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. If a Bandwidth Metric sub-TLV is advertised for a
link, the Flex-Algorithm calculation MUST use the Bandwidth Metric
advertised on the link, and MUST NOT use the automatically derived
metric for that link.
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4.3.2. Bandwidth Thresholds sub-TLV
This section provides FAD constraint advertisement details for the
Bandwidth Thresholds method of metric calculation as described in
Section 4.2.2. The Flexible Algorithm Definition Bandwidth Threshold
Sub-TLV (FADBT Sub-TLV) 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 |G| Flags. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Threshold 1 Min. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Metric 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Threshold 1 Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Metric 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Threshold 2 Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Metric n-1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Threshold n-1 Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Metric n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 1 + n*7 octets. Here n is equal to number of Threshold Metrics specified.
n MUST be greater than or equal to 2.
Flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|G| | | |
+-+-+-+-+-+-+-+-+
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G-flag: when set, interface group Mode MUST be used to derive total link bandwidth.
Staircase bandwidth threshold and associated metric values.
Bandwidth Threshold 1 Min.: Minimum Link Bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Bandwidth Threshold 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 - 4,261,412,864)
Figure 9: ISIS FADBT sub-TLV
When G-flag is set, the cumulative bandwidth of the parallel links is
computed as described in section Section 4.1.2. If G-flag is not
set, the advertised Maximum Link Bandwidth is used.
When the computed link bandwidth is less than Bandwidth Threshold 1
Min, the MAX_METRIC value of 4,261,412,864 MUST be assigned as the
Bandwidth Metric on the link during Flex-Algorithm SPF calculation.
When the computed link bandwidth is greater than or equal to
Bandwidth Threshold 1 Min AND less than Bandwidth Threshold 1 Max,
Threshold Metric 1 MUST be assigned as the Bandwidth Metric on the
link during Flex-Algorithm SPF calculation.
Similarly, when the computed link bandwidth is greater than or equal
to Bandwidth Threshold 1 Max AND less than Bandwidth Threshold 2 Max,
Threshold Metric 2 MUST be assigned as the Bandwidth Metric on the
link during Flex-Algorithm SPF calculation.
Similarly, when the computed link bandwidth is greater than or equal
to Bandwidth Threshold n-1 Max, Threshold Metric n MUST be assigned
as the Bandwidth Metric on the link during Flex-Algorithm SPF
calculation.
The ISIS FADBT 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.
A FAD MUST NOT contain both FADBT sub-TLV and FADRB sub-TLV. If both
these sub-TLVs are advertised in the same FAD for a Flexible
Algorithm, the FAD must be ignored by the receiver.
If a Bandwidth Metric sub-TLV is advertised for a link, the Flex-
Algorithm calculation MUST use the Bandwidth Metric advertised on the
link, and MUST NOT use the automatically derived metric for that
link.
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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 |G| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reference Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Round-Off Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 14 octets.
Reference Bandwidth: Bandwidth encoded in 32 bits in IEEE floating point
format. The units are in bytes per second.
Round-Off Bandwidth: Bandwidth encoded in 32 bits in IEEE floating point
format. The units are in bytes per second.
Flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|G| | | |
+-+-+-+-+-+-+-+-+
G-flag: when set, interface group Mode MUST be used
to derive total link bandwidth.
Metric calculation: (Reference_bandwidth) /
(Total_link_bandwidth -
(Modulus of(Total_link_bandwidth, Round_off_bw)))
Figure 10: OSPF FADRB sub-TLV
Round-off Bandwidth value is used to make sure the metric does not
change when there is smaller change in the link bandwidth. The OSPF
FADRB Sub-TLV MUST NOT appear more than once in an OSPF FAD TLV. If
it appears more than once, the OSPF FAD TLV MUST be ignored by the
receiver. If a Bandwidth Metric sub-TLV is advertised for a link,
the Flex-Algorithm calculation MUST use the Bandwidth Metric
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advertised on the link, and MUST NOT use the automatically derived
metric for that link.
4.4.2. Bandwidth Threshold sub-TLV
The Flexible Algorithm Definition Bandwidth Thresholds Sub-TLV (FADBT
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 |G| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Threshold 1 Min. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Metric 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Threshold 1 Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Metric 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Threshold 2 Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Metric n-1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Threshold n-1 Max. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold Metric n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: 2 + n*8 octets. Here n is equal to number of Threshold Metrics specified.
n MUST be greater than or equal to 2.
Flags:
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0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|G| | | |
+-+-+-+-+-+-+-+-+
G-flag: when set, interface group Mode MUST be used to derive total link bandwidth.
Staircase bandwidth threshold and associated metric values.
Bandwidth Threshold 1 Min.: Minimum Link Bandwidth is encoded in 32 bits in IEEE
floating point format. The units are bytes per second.
Bandwidth Threshold 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)
Figure 11: OSPF FADBT sub-TLV
When G-flag is set, the cumulative bandwidth of the parallel links is
computed as described in section Section 4.1.2. If G-flag is not
set, the advertised Maximum Link Bandwidth is used.
When the computed link bandwidth is less than Bandwidth Threshold 1
Min, the MAX_METRIC value of 4,294,967,296 MUST be assigned as the
Bandwidth Metric on the link during Flex-Algorithm SPF calculation.
When the computed link bandwidth is greater than or equal to
Bandwidth Threshold 1 Min AND less than Bandwidth Threshold 1 Max,
Threshold Metric 1 MUST be assigned as the Bandwidth Metric on the
link during Flex-Algorithm SPF calculation.
Similarly, when the computed link bandwidth is greater than or equal
to Bandwidth Threshold 1 Max AND less than Bandwidth Threshold 2 Max,
Threshold Metric 2 MUST be assigned as the Bandwidth Metric on the
link during Flex-Algorithm SPF calculation.
Similarly, when the computed link bandwidth is greater than or equal
to Bandwidth Threshold n-1 Max, Threshold Metric n MUST be assigned
as the Bandwidth Metric on the link during Flex-Algorithm SPF
calculation.
The OSPF FADBT Sub-TLV MUST NOT appear more than once in an OSPF FAD
TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored
by the receiver.
A FAD MUST NOT contain both FADBT sub-TLV and FADRB sub-TLV. If both
these sub-TLVs are advertised in the same FAD (winner FAD) for a
Flexible Algorithm, the receiving nodes MUST stop participating in
such Flexible-Algorithm
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If a Bandwidth Metric sub-TLV is advertised for a link, the Flex-
Algorithm calculation MUST use the Bandwidth Metric advertised on the
link, and MUST NOT use the automatically derived metric for that
link.
5. Bandwidth metric considerations
This section specifies the rules of deriving the Bandwidth Metric if
and only if the winning FAD for the Flex-Algorithm specifies the
metric-type as "Bandwidth Metric".
1. If the the Bandwidth Metric sub-TLV is advertised for the link
as described in Section 2, it MUST be used during the Flex-
Algorithm calculation.
2. If the Bandwidth Metric sub-TLV is not advertised for the link
and the winning FAD for the Flex-Algorithm does not specify the
automatic bandwidth metric calculation (as defined in Section 4 ),
the Bandwidth Metric is considered as not being advertised for the
link.
3. If the Bandwidth Metric sub-TLV is not advertised for the link
and the winning FAD for the Flex-Algorithm specifies the automatic
bandwidth metric calculation (as defined in Section 4), the
Bandwidth Metric metric MUST be automatically calculated as per
the procedures defined in Section 4. If the Bandwidth Metric can
not be calculated due to lack of Flex-Algorithm specific ASLA
advertisement of sub-sub-TLV 9 [RFC 8919], or in case of IS-IS, in
presence of the L-Flag in the Flex-Algorithm specific ASLA
advertisement the lack of sub-TLV 9 in the TLV 22/222/23/223/141
[RFC 5305], the Bandwidth Metric is considered as not being
advertised for the link.
6. Calculation of Flex-Algorithm paths
Two new additional rules are added to the existing rules in the Flex-
rules specified in sec 13 of [I-D.ietf-lsr-flex-algo].
6. Check if any exclude FAEMB rule is part of the Flex-Algorithm
definition. If such exclude rule exists and the link has Maximum
Link Bandwidth advertised, check if the link bandwidth satisfies
the FAEMB rule. If the link does not satisfy the FAEMB rule, the
link MUST be pruned from the computation.
7. Check if any exclude FAEMD rule is part of the Flex-Algorithm
definition. If such exclude rule exists and the link has Min
Unidirectional link delay advertised, check if the link delay
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satisfies the FAEMD rule. If the link does not satisfy the FAEMD
rule, the link MUST be pruned from the computation.
7. Backward Compatibility
8. Security Considerations
TBD
9. IANA Considerations
9.1. IGP Metric-Type Registry
Type: Suggested 3 (TBA)
Description: Bandwidth metric
Reference: This document
9.2. 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
Reference: This document Section 4.3.1
Type: Suggested 9 (TBA)
Description: ISIS Threshold Metric sub-TLV
Reference: This document Section 4.3.2
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9.3. 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
9.4. Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223
Type: Suggested 45 (TBA)
Description: Bandwidth metric
Reference: This document Section 2.1
9.5. Sub-sub-TLV Codepoints for Application-Specific Link Attributes
Type: Suggested 45 (TBA)
Description: Bandwidth metric
Reference: This document Section 2.1
9.6. OSPFv2 Extended Link TLV Sub-TLVs
Type: Suggested 45 (TBA)
Description: Bandwidth metric
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Reference: This document Section 2.2
9.7. Types for sub-TLVs of TE Link TLV (Value 2)
Type: Suggested 45 (TBA)
Description: Bandwidth metric
Reference: This document Section 2.2
10. Acknowledgements
Many thanks to Chris Bowers, Krzysztof Szarcowitz, Julian Lucek, Ram
Santhanakrishnan for discussions and inputs.
11. Contributors
1. Salih K A
Juniper Networks
salih@juniper.net
12. References
12.1. 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>.
[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>.
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[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>.
12.2. 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>.
Authors' Addresses
Shraddha Hegde
Juniper Networks Inc.
Exora Business Park
Bangalore, KA 560103
India
Email: shraddha@juniper.net
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William Britto
Juniper Networks Inc.
Email: bwilliam@juniper.net
Rajesh Shetty
Juniper Networks Inc.
Email: mrajesh@juniper.net
Bruno Decraene
Orange
Email: bruno.decraene@orange.com
Peter Psenak
Cisco Systems
Email: ppsenak@cisco.com
Tony Li
Arista Networks
Email: tony.li@tony.li
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