Internet DRAFT - draft-peng-lsr-flex-algo-opt-slicing
draft-peng-lsr-flex-algo-opt-slicing
L P. Shaofu
Internet-Draft C. Ran
Intended status: Standards Track ZTE Corporation
Expires: March 9, 2021 G. Mirsky
ZTE Corp.
September 5, 2020
IGP Flexible Algorithm Optimazition for Netwrok Slicing
draft-peng-lsr-flex-algo-opt-slicing-02
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 extends the use of the IGP Flex Algorithm to to be more
suitable for network slicing scenarios.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 9, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. SR Policy Using Slice-based Resources . . . . . . . . . . . . 3
4. SR Policy Optimaztion with IGP Flex-algo . . . . . . . . . . 3
5. IGP Flex-algo Enhancement with AII . . . . . . . . . . . . . 5
5.1. Enhancement for TI-LFA . . . . . . . . . . . . . . . . . 5
5.2. Enhancement for Inter-domain . . . . . . . . . . . . . . 5
5.3. Enhancement for L2bundles . . . . . . . . . . . . . . . . 6
6. QoS Policy per AII/Algorithm . . . . . . . . . . . . . . . . 6
7. AII of FAD Sub-TLV . . . . . . . . . . . . . . . . . . . . . 7
7.1. ISIS AII of FAD Sub-TLV . . . . . . . . . . . . . . . . . 7
7.2. OSPF AII of FAD Sub-TLV . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. ISIS IANA Considerations . . . . . . . . . . . . . . . . 8
8.2. OSPF IANA Considerations . . . . . . . . . . . . . . . . 9
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
11. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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 (SR)
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).
[I-D.peng-teas-network-slicing] proposes a solution to extend the
control plane of transport network to instantiate the Network Slice
Instance (NSI) in transport network. A new identifier, AII, instead
of existing TE affinity or other identifiers, is introduced to
represent a TN-slice and specify the dedicated resource for the TN-
slice.
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This document extends the FAD of IGP Flex Algorithm to let IGPs
compute constraint based paths limited in specific TN-slice.
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. SR Policy Using Slice-based Resources
[I-D.ietf-spring-segment-routing-policy] details the concepts of SR
Policy and steering into an SR Policy. These apply equally to the
MPLS and IPv6 (known as SRv6) data plane instantiations of Segment
Routing with their respective representations of segments as SR-MPLS
SID and SRv6 SID as described in [RFC8402]. The color of SR policy
defines a TE purpose, which includes a set of constraints such as
bandwidth, delay, TE metric, etc.
The overlay service can select underlay SR policy according to a
meaningful color value. From the perspective of service, color is
the key to get the expected SLA, and it is a global administrative
configuration or setting that could be exchangeable between two
devices for SR policy on-demand next-hop triggering. The service
never concern whether the underlay network has been partitioned as
multi-domains, or multi-topologies. That is, color has not semantic
local within one domain, or one topology. Instead, any type of
resources such as topology, computation, storage could be selected by
the color template. In this sense, TN-slices are also high-level
resouces that could be selected by color template. A simple way to
achieve this is to contain the specific AII information in the color
template, to restrict the TE path to the corresponding TN-slice.
4. SR Policy Optimaztion with IGP Flex-algo
Indeed, FA-id defined in [I-D.ietf-lsr-flex-algo] is a short mapping
of SR policy color to optimaze segment stack depth for the IGP area
partial of the entire SR policy. The overlay service that want to be
carried over a particual SR-FA path must firstly let the SR policy
supplier know that requirement. There are two possible ways to map a
color to an FA-id. One is explicit mapping configuration within
color template, the other is dynamic to replace a long segment list
to a single FA segment by headend or controller once the creteria
contained in the color-template equal to that contained in FAD.
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In addtion to the above mapping mode, merging mode is also possible.
In this case, the computation engine will combine the constraints
contained in the expanded FAD with other constraints in the color
template. This is to continue to iterate TE business in FA plane.
The iteration means the best-effort path itself within an FA plane is
exactly constraint based path, but operators can define more
constraints in that FA plane. The computed strict path can be
optimized to a loose path when a part of the strict path is
consistent with the algorithm based path, i.e, some consecutive
adjacency SIDs can be replaced with a single algorithm based prefix
SID. Note that the loose optimization in this case, i.e, an SR
policy created in FA plane, is similar with that when an SR policy is
created in physical network, and that is different with optimization
of segment stack depth using Flex-algo.
[I-D.ietf-lsr-flex-algo] described that application specific Flex-
Algorithm participation advertisements MAY be topology specific or
MAY be topology independent, and also emphasize that for Segment
Routing application, the Flex-Algorithm participation advertisement
is topology independent, i.e., when a router advertises participation
in an SR-Algorithm, the participation applies to all topologies in
which the advertising node participates. Here the topology means
Multi-Topology Routing (MTR) described in [RFC5120], [RFC4915],
[RFC5340]. [RFC8402] also mentioned that multiple SIDs MAY be
allocated to the same prefix so long as the tuple <prefix, topology,
algorithm> is unique. In fact, this will lead to many forwarding
tables, such as table per MTR, table per each combined tuple <MTR,
algorithm>, and make traffic steering very complicated.
According to [I-D.peng-teas-network-slicing], we donot use MTR to
identify the TN-slice and partition the virtual topology for the TN-
slice. Instead, a slice-based identifier, AII, is introduced to
represent a TN-slice. The first feature of AII is a TE criteria for
TE service just like AG/EAG. So that AII, like other constraints,
can be included in color template. When an SR policy uses Flex-algo
for stack depth optimization, in order to make the contents of the
color template and the mapping FAD consistent, AII is also necessary
put into the mapping FAD.
Although the network operator may change the AII information within
the FAD for the specific FA-id, there is only one forwarding table
with constant table ID, i.e., FA-id. Note that there are also
independent forwarding tables per AII for other purpose, but not
those per tuple <AII, FA-id>. That is, FA-id has not semantic local
within AII, just as color is not part of the topology.
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5. IGP Flex-algo Enhancement with AII
FAD that contains AII information will enhance the capability of
Flex-algo to support network slicing.
5.1. Enhancement for TI-LFA
Loop Free Alternate (LFA) paths for a given Flex-Algorithm can
include Prefix-SIDs advertised specifically for the given algorithm,
and especially Adjacency-SIDs for the specific AII. When different
FA planes share the same link resouce, Adjacency-SID per AII
(according to [I-D.peng-teas-network-slicing]) can distinguish the
flow of different slices well and provide different treatment.
The following figure shows an example of Flex-algo enhancement with
AII.
[S1]--------[D]--------[S2]
| | |
| | |
| | |
[A]---------[B]--------[C]
Figure 1: Flex-algo LFA Enhancement with AII
Suppose that node S1, A, B, D and their inter-connected links belongs
to FA-id 128 plane as well as AII-1, and S2, B, C, D and their inter-
connected links belongs to FA-id 129 plane as well as AII-2. The IGP
metric of link B-D is 100, and all other links have IGP metric 1. In
FA-id 128 plane, from S1 to destination D, the primary path is S1-D,
and the TI-LFA backup path is segment list {node(B), adjacency(B-D)}.
Similarly, In FA-id 129 plane, from S2 to destination D, the primary
path is S2-D, and the TI-LFA backup path is segment list {node(B),
adjacency(B-D)}. With the help of AII parameter contained in the FAD,
the above TI-LFA path of FA-id 128 plane will be translated to {node-
SID(B)@FA-id128, adjacency-SID(B-D)@AII-1}, and TI-LFA path of FA-id
129 plane will be translate to {node-SID(B)@FA-id129, adjacency-
SID(B-D)@AII-2}. So that node B can distinguish the flow of FA-id 128
and FA-id 129 with different treatment (e.g., QoS) and send to the
same outgoing link B-D.
5.2. Enhancement for Inter-domain
For inter-domain case, different domain can config different FA-id
independently, but they can contain the same AII to construct an E2E
slice-based SR policy. IGP flex-algo is responsible for creating
constraint based paths within the domain according to FAD including
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AII parameter, and BGP-LU or SDN controller is responsible for
selecting inter-domain links according to color template including
AII parameter. AII is easy to address the requirement of E2E Slicing
view.
5.3. Enhancement for L2bundles
[RFC8668] inroduced L2 Bundle Member Attributes sub-TLV to be
advertised within ISIS TLV-22/23/141/222/223. It may define an
attribute common to all of the bundle members listed and an attribute
individual to each L2 Bundle Member. [RFC8668] mainly defined
Adjacency-SID for each L2 Bundle Member, that is very useful to
isolate flows among different slices. A typical deployment of hard
slicing is that different L2 Bundle Member, e.g, Flex-E channel,
belongs to different TN-slice, so a specific Adjacency-SID for a
specific L2 Bundle Member will steer the packets to that member.
However, the link resource of an FA plane is selected according to
the TE affinity attribute of all L3 links joining to the IGP instance
and the INCLUDE/EXCLUDE rules contained in the FAD. If we want to
let different L2 Bundle Member belongs to different FA plane, it must
determine the TE affinity of each L2 Bundle Member. There could have
two methods:
o [I-D.zch-lsr-isis-network-slicing] extends ISIS protocol to carry
AII (TN-slice ID) information for each L2 Bundle Member within L2
Bundle Member Attributes sub-TLV defined in [RFC8668]. Even
though the same L3 parrent link can be joined to multiple FA
planes according to TE affinity INCLUDE/EXCLUDE rules, it is easy
for each FA plane to exactly use the specific L2 Bundle Member
according to the AII information contained in FAD.
o It is also possible to directly define AG/EGA per L2 Bundle Member
for Flex-algo application. [I-D.peng-lsr-flex-algo-l2bundles]
described how to create Flex-algo plane in the case of L2bundles
scenario, by explicit AG/EGA affinity configuration for each L2
Bundle Member. This method is similar with the above definition
of AII per L2 Bundle Member, both them can distinguish traffic of
different hard slice.
It is possible to include only AII, or only TE affinity, or both AII
and TE affinity, in an FAD.
6. QoS Policy per AII/Algorithm
Due to SID allocation per algorithm, flows belonging to different FA
planes can be easily distinguished by incoming SID of the received
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packets, so that different QoS policies can be applied to different
FA packets on the same link.
Depending on the implementation, operators can configure multiple QoS
policies each for different algorithm on the same link. One of the
difficulties is that during this configuration phase it is not
straightforward for a link to be included in an FA plane, as this can
only be determined after all nodes in the network have negotiated the
FAD. A simple way is that as long as a node enable an FA, all its
links are configured with that algorithm based QoS policy.
Depending on the implementation, operators can also configure
multiple QoS policies each for different AII on the same link. An
AII based QoS policy is configured to a subset of links who join the
related TN-slice explicitly.
Depending on the implementation, the queue resources of the link can
be divided according to AII, algorithm, or their combination. When
the received pachet matched an flex-algo related FIB entry, it will
be directed to the queue dedicated to that algorithm. If the FIB
entry is created according to the FAD including AII creteria, the
packets can further schedule queue resouce according to AII.
7. AII of FAD Sub-TLV
7.1. ISIS AII of FAD Sub-TLV
ISIS AII of FAD Sub-TLV is used to advertise the AII information that
is used during the Flex-Algorithm path calculation. It 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: ISIS AII of FAD Sub-TLV format
where:
Type: TBD1.
Length: 4 octets.
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AII: Administrative Instance Identifier as defined in
[I-D.peng-teas-network-slicing].
ISIS AII of FAD Sub-TLV MAY 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.
7.2. OSPF AII of FAD Sub-TLV
OSPF AII of FAD Sub-TLV is used to advertise the AII information that
is used during the Flex-Algorithm path calculation. It 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: OSPF AII of FAD Sub-TLV format
where:
Type: TBD2.
Length: 4 octets.
AII: Administrative Instance Identifier as defined in
[I-D.peng-teas-network-slicing].
OSPF AII of FAD Sub-TLV MAY 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.
8. IANA Considerations
8.1. ISIS IANA Considerations
This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs
for Flexible Algorithm Definition Sub-TLV" registry:
Type: TBD1
Description: Administrative Instance Identifier
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Reference: This document (Section 6.1)
8.2. OSPF IANA Considerations
This document registers following Sub-TLVs in the "TLVs for Flexible
Algorithm Definition TLV" registry:
Type: TBD2
Description: Administrative Instance Identifier
Reference: This document (Section 6.2)
9. Security Considerations
This specification inherits all security considerations of
[I-D.ietf-lsr-flex-algo].
10. Acknowledgements
TBD
11. 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-10 (work in progress), August 2020.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-08 (work in progress),
July 2020.
[I-D.peng-lsr-flex-algo-l2bundles]
Peng, S., Chen, R., and G. Mirsky, "IGP Flexible Algorithm
with L2bundles", draft-peng-lsr-flex-algo-l2bundles-02
(work in progress), August 2020.
[I-D.peng-teas-network-slicing]
Peng, S., Chen, R., Mirsky, G., and F. Qin, "Packet
Network Slicing using Segment Routing", draft-peng-teas-
network-slicing-03 (work in progress), February 2020.
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[I-D.zch-lsr-isis-network-slicing]
Zhu, Y., Chen, R., Peng, S., and F. Qin, "IS-IS Extensions
to Support Transport Network Slices using Segment
Routing", draft-zch-lsr-isis-network-slicing-06 (work in
progress), September 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>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
[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>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[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>.
[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
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Peng Shaofu
ZTE Corporation
No.68 Zijinghua Road, Yuhuatai District
Nanjing
China
Email: peng.shaofu@zte.com.cn
Chen Ran
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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