Internet DRAFT - draft-peng-lsr-flex-algo-l2bundles
draft-peng-lsr-flex-algo-l2bundles
L Y. Zhu
Internet-Draft China telecom
Intended status: Standards Track S. Peng
Expires: June 10, 2021 R. Chen
ZTE Corporation
G. Mirsky
ZTE Corp.
December 7, 2020
IGP Flexible Algorithm with L2bundles
draft-peng-lsr-flex-algo-l2bundles-05
Abstract
IGP Flex Algorithm proposes a solution that allows IGPs themselves to
compute constraint based paths over the network, and it also
specifies a way of using Segment Routing (SR) Prefix-SIDs and SRv6
locators to steer packets along the constraint-based paths. This
document describes how to create Flex-algo plane with L2bundles
scenario.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Color set on L2 Bundle Member . . . . . . . . . . . . . . . . 3
4. Flex-algo plane with L2 link resource . . . . . . . . . . . . 3
4.1. Best-effort . . . . . . . . . . . . . . . . . . . . . . . 3
4.2. Traffic Engineering . . . . . . . . . . . . . . . . . . . 4
5. Flex-algo L2bundles Use-cases . . . . . . . . . . . . . . . . 5
5.1. Flex-algo L2bundles Examples . . . . . . . . . . . . . . 5
6. IGP L2 Bundle Member Extensions . . . . . . . . . . . . . . . 6
6.1. ISIS L2 Bundle Member EAG advertisement . . . . . . . . . 6
6.2. OSPF L2 Bundle Member EAG advertisement . . . . . . . . . 6
6.3. FAD Flags Extensions . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
IGP Flex Algorithm [I-D.ietf-lsr-flex-algo] proposes a solution that
allows IGPs themselves to compute constraint based paths over the
network, and it also specifies a way of using Segment Routing
[RFC8402] Prefix-SIDs and SRv6 locators to steer packets along the
constraint-based paths. It specifies a set of extensions to ISIS,
OSPFv2 and OSPFv3 that enable a router to send TLVs that identify (a)
calculation-type, (b) specify a metric-type, and (c )describe a set
of constraints on the topology, that are to be used to compute the
best paths along the constrained topology. A given combination of
calculation-type, metric-type, and constraints is known as an FAD
(Flexible Algorithm Definition).
[RFC8668] and [I-D.ketant-lsr-ospf-l2bundles] introduces the ability
for IS-IS and OSPF respectively to advertise the link attributes of
Layer 2 (L2) Bundle Members. Especially, the link attribute
"Administrative Group" and "Extended Administrative Group" could be
individual to each L2 Bundle Member for purpose of Flex-algo plane
construction, where multiple Flex-algo planes share the same Layer 3
parent interface and each Flex-algo plane has dedicated L2 Bundle
Member.
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This document describes how to create Flex-algo plane with L2bundles
scenario.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Color set on L2 Bundle Member
Traffic Engineering affinity (also termed as Color) is often to be
set on the Layer 3 interface and be flooded by IGP-TE. However, when
the Layer 3 interface is a Layer 2 interface bundle, operators can
config individual color for each L2 Bundle Member. So that IGP link-
state database will contain the TE affinity attribute of L2 Bundle
Member, as well as Layer 3 parrent interface.
Note that Layer 3 interface can join to IGP instance explicitly, but
L2 Bundle Member not.
The TE affinity of the Layer 3 parrent interface can be a combined
value of all L2 Bundle Members. For example, if the Layer 3 parrent
interface contains three L2 Bundle Members, each with color "RED",
"GREEN", "BLUE" respectively, the Layer 3 parrent interface will have
color "RED|GREEN|BLUE".
4. Flex-algo plane with L2 link resource
4.1. Best-effort
[I-D.ietf-lsr-flex-algo] defines the color-based link resource
selection rules in FAD to construct the expected Flex-algo plane.
Each node in the Flex-algo plane will maintain the best path to other
destination nodes. In the case of L2bundles scenario, each node need
check the outgoing Layer 2 bundle interface, to see which L2 Bundle
Member does exactly belong to the Flex-algo plane.
For the node who originate the l2-bundle interface, the forwarding
information of the FIB entry with outgoing Layer 2 bundle interface
will exactly select the L2 Bundle Member that belongs to the Flex-
algo plane to forward packets.
For example, three Flex-algo plane share the same Layer 3 parrent
interface including three L2 Bundle Members each with color "RED",
"GREEN", "BLUE" respectively, and each Flex-algo plane with link
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selection rule "Include-Any RED", "Include-Any GREEN", "Include-Any
BLUE" respectively, Flex-algo SHOULD NOT simply select the Layer 3
parrent interface for all Flex-algo plane, but need continue to
select individual L2 Bundle Member for each specific Flex-algo plane.
As a reslut, the FIB entry within Flex-algo RED plane will exactly
choose the L2 Bundle Members with color "RED" to forward packets, the
FIB entry within Flex-algo GREEN plane will exactly choose the L2
Bundle Members with color "GREEN" to forward packets, and the FIB
entry within Flex-algo BLUE plane will exactly choose the L2 Bundle
Members with color "BLUE" to forward packets.
The above processing is a local optimization for each node who
originate l2-bundle interface.
In addition, for a remote node which received l2-bundle advertisement
originated from other nodes, if that l2-bundle is in the flex-algo
based path to a destination node, it must confirm which L2 Bundle
Member belongs to the flex-algo plane and check that L2 Bundle Member
really meets the constraints defined in the related FAD. This
processing is necessary when Flex-algo is used to optimize SID stack
depth for an SR-TE policy, e.g, the SR-TE policy defines TE affinity
to select individual L2 Bundle Member and the SID list may contain
Adjacency-SID for a specific L2 Bundle Member as described in
[RFC8668] and [I-D.ketant-lsr-ospf-l2bundles]. Thus the flex-algo
based path must be consistent with the original path of the optimized
SR-TE policy, i.e, within the flex-algo plane when each node
determine its next-hop towards a destination, the determination must
be based on the above confirmation and check of L2 Bundle Members.
4.2. Traffic Engineering
A segment list contains SIDs advertised specifically for the given
algorithm is possible, such as an inter-domain path contains multiple
Flex-algo domains, a TI-LFA backup path within the Flex-algo plane,
or an optimized TE path avoiding congested link within the Flex-algo
plane. When the headend or controller compute these SR-TE paths
within the specific flex-algo plane, in addition to the algorithm
based Prefix-SID towards the loose node, an Adjacency-SID can also be
used to strictly steer the packets along the expected L3 link.
However, if the L3 link is a l2-bundle interface, it is necessary to
see which L2 Bundle Member exactly belongs to the specific Flex-algo
plane and use the Adjacency-SID for that member.
[RFC8668] and [I-D.ketant-lsr-ospf-l2bundles] have defined Adjacency-
SID for each L2 Bundle Member, that can be used to isolate flows
among multiple Flex-algo planes, when these Flex-algo planes share
the same Layer 3 parrent interface. A specific Adjacency-SID for a
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specific L2 Bundle Member can be contained in the SID list of the SR
path within the flex-algo plane and steer the packets to that member.
5. Flex-algo L2bundles Use-cases
In some operator's networks, a large number of bundled links are
deployed to improve the bandwidth. However, for a specific l2bundle,
each member has different capabilities, such as different delay,
bandwidth, AG/EAG, etc. When the path of an SR policy needs to go
through an Layer 2 interface bundle, operators want to choose the
individual member link to meet business requirements. Different SR
policy may choose different member links, according to different set
of constraints.
When Flex algorithm is enabled in the above networks, even all flex-
algo planes share all Layer 2 interface bundles, i.e, all FA planes
have the same structure, an important requirement to Flex-algo is
that the constraint based computation of Flex-algo must consider how
to select member links to meet service's criterias. In addition,
different flex-algo planes can also have different structures, with
different set of nodes and links, to meet more strict business
requirements.
The extended behavior of flex-algo introduced in this document can
meet the above requirement, and exactly it is independent with the
structure of flex-algo plane.
5.1. Flex-algo L2bundles Examples
Let's describe the requirement with the following example.
S======A=====B======C=====D
\ /
\___________E__________/
Figure 1: Flex-algo L2bundles Example
An SR policy from headend S to endpoint D is created, with color
template {min delay}. Suppose the macthed link is the upper member
link of l2bundles interface between S-A, A-B, B-C, C-D. All of them
have delay 10ms. So that the computed segment list would be <adj-
sid@upper-link-of-S-A, adj-sid@upper-link-of-A-B, adj-sid@upper-link-
of-B-C, adj-sid@upper-link-of-C-D>.
Suppose the delay of the lower member link of l2bundles interface
between S-A, A-B, B-C, C-D are all 100ms. That means the delay of
the bundles L3 interface between S-A, A-B, B-C, C-D are all 100ms
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(i.e, subject to the member who have the largest delay). Also
suppose the delay of the L3 link between S-E, E-D are all 50ms.
If flex-algo (eg, algorithm 128) is enabled in the above network to
optimize the stack depth of the above SR polcy, the related FAD would
also be {min delay}. However, if all nodes in the network only see L3
interface resouce, then at node S the computed result to destination
D would be next-hop E, and at node E the computed result to
destination D would be next-hop D. Obviously, after stack
optimization the flex-algo path S-E-D is not consistent with the
original path (S-A-B-C-D) of SR policy.
Thus it will be benefit for flex-algo to see L2 member link during
CSPF computation. And, each node in the network, instead of only
headend, must perform the same behavior to check L2 member link
resouce, otherwise there may be a loop.
6. IGP L2 Bundle Member Extensions
6.1. ISIS L2 Bundle Member EAG advertisement
[RFC8668] defined TLV-25 for ISIS to advertise the link attributes of
L2 Bundle Members, and mentioned that the traditional "Administrative
group (color) Sub-TLV" and "Extended Administrative Group Sub-TLV"
may appear in TLV-25 and MAY be shared by multiple L2 Bundle Members.
If we want to advertise unique EAG values for each bundle member, we
can use multiple L2 Bundle Attribute Descriptors with each specify a
single bundle member. So it is sufficient to construct Flex-algo
plane to select L2 link resource.
6.2. OSPF L2 Bundle Member EAG advertisement
[I-D.ketant-lsr-ospf-l2bundles] defined "L2 Bundle Member Attributes
sub-TLV" for OSPF/OSPFv3 to advertise the link attributes of L2
Bundle Members, and mentioned that the traditional "Administrative
group (color) Sub-TLV" and "Extended Administrative Group Sub-TLV"
are applicable in "L2 Bundle Member Attributes sub-TLV". Because
there is "L2 Bundle Member Attributes sub-TLV" per L2 Bundle Member,
it is also sufficient to construct Flex-algo plane to select L2 link
resource.
6.3. FAD Flags Extensions
A new flag (L-flag) is introduced to both ISIS Flexible Algorithm
Definition Flags Sub-TLV and OSPF Flexible Algorithm Definition Flags
Sub-TLV (defined in [I-D.ietf-lsr-flex-algo]), to let each node to
check L2 member link resouce of interface bundle during flex-
algorithm path calculation.
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0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|M|L| | ...
+-+-+-+-+-+-+-+-+...
Figure 2
where:
L-flag: introduced by this document. When set, the traffic
engineering resouce or attributes of L2 member link of interface
bundle MUST be checked and used during flex-algorithm path
calculation.
7. IANA Considerations
This document need not define new sub-TLV to IGP for Flex-algo
combined with l2bundles.
8. Security Considerations
There are no new security issues introduced by the extensions in this
document.
9. Acknowledgements
TBD
10. 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.
[I-D.ketant-lsr-ospf-l2bundles]
Talaulikar, K. and P. Psenak, "Advertising L2 Bundle
Member Link Attributes in OSPF", draft-ketant-lsr-ospf-
l2bundles-02 (work in progress), June 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>.
[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>.
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[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
M., and E. Aries, "Advertising Layer 2 Bundle Member Link
Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
December 2019, <https://www.rfc-editor.org/info/rfc8668>.
Authors' Addresses
Yongqing Zhu
China telecom
Email: zhuyq8@chinatelecom.cn
Shaofu Peng
ZTE Corporation
No.68 Zijinghua Road, Yuhuatai District
Nanjing
China
Email: peng.shaofu@zte.com.cn
Ran Chen
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing
China
Email: chen.ran@zte.com.cn
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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