SPRING Working Group J. Dong
Internet-Draft Huawei Technologies
Intended status: Standards Track S. Bryant
Expires: August 26, 2021 Futurewei Technologies
T. Miyasaka
KDDI Corporation
Y. Zhu
China Telecom
F. Qin
Z. Li
China Mobile
F. Clad
Cisco Systems
February 22, 2021
Introducing Resource Awareness to SR Segments
draft-ietf-spring-resource-aware-segments-02
Abstract
This document describes the mechanism to associate network resource
attributes to Segment Routing Identifiers (SIDs). Such SIDs are
referred to as resource-aware SIDs in this document. The resource-
aware SIDs retain their original forwarding semantics, but with the
additional semantics to identify the set of network resources
available for the packet processing action. The resource-aware SIDs
can therefore be used to build SR paths or virtual networks with a
set of reserved network resources. The proposed mechanism is
applicable to both segment routing with MPLS data plane (SR-MPLS) and
segment routing with IPv6 data plane (SRv6).
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-
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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 August 26, 2021.
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Copyright Notice
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Segments with Resource Awareness . . . . . . . . . . . . . . 3
2.1. SR-MPLS . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. SRv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Control Plane Considerations . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Segment Routing (SR) [RFC8402] specifies a mechanism to steer packets
through an ordered list of segments. A segment is referred to by its
Segment Identifier (SID). With SR, explicit source routing can be
achieved without introducing per-path state into the network.
Compared with RSVP-TE [RFC3209], currently SR does not have the
capability of reserving network resources or identifying a set of
network resources reserved for individual services or customers.
Although a centralized controller can have a global view of network
state and can provision different services using different SR paths,
in data packet forwarding it still relies on traditional DiffServ QoS
mechanism [RFC2474] [RFC2475] to provide coarse-grained traffic
differentiation in the network. While such kind of mechanism may be
sufficient for some types of services, some customers or services may
require a set of dedicated network resources to be allocated in the
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network to achieve resource isolation from other customers/services
in the same network. Also note the number of such customers or
services can be larger than the number of traffic classes available
with DiffServ QoS.
This document extends the SR paradigm without the need of defining
new SID types by associating SIDs with network resource attributes.
These resource-aware SIDs retain their original functionality, with
the additional semantics of identifying the set of network resources
available for the packet processing action. One typical type of the
network resource is the link bandwidth and the associated
buffer/queuing/scheduling resources, but it is also possible to
associate SR SIDs with other types of resources (e.g., processing or
storage resources). On a particular network segment, multiple
resource-aware SIDs can be allocated, each of which represents a
subset of network resources allocated in the network to meet the
requirement of individual customers or services. The allocation of
network resources on network segments can be done either via local
configuration or via a centralized controller. Other approaches are
possible such as use of a control protocol signaling, but they are
for further study. Each set of network resources can be associated
with one or multiple resource-aware SIDs. These resource-aware SIDs
can be used to build SR paths with a set of reserved network
resources, which can be used to carry service traffic which requires
dedicated network resources along the path. The resource-aware SIDs
can also be used to build SR based virtual networks for services with
the required network topology and resource attributes. The proposed
mechanism is applicable to SR with both MPLS data plane (SR-MPLS) and
IPv6 data plane (SRv6).
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.
2. Segments with Resource Awareness
In segment routing architecture [RFC8402], several types of segments
are defined to represent either topological or service instructions.
A topological segment can be a node segment or an adjacency segment.
A service segment may be associated with specific service functions
for service chaining purpose. This document introduces additional
resource semantics to these existing types of SIDs, so that the SIDs
can be used to identify the topology or service functions, and also
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the set of network resources allocated on the network segments for
packet processing.
This section describes the mechanisms of using SR SIDs to identify
the additional resource information associated with SR paths or
virtual networks based on the two SR data plane instantiations: SR-
MPLS and SRv6. The mechanisms to identify the forwarding path or
network topology with SIDs as defined in [RFC8402] can be reused, and
the control plane can be based on [RFC4915], [RFC5120] and
[I-D.ietf-lsr-flex-algo].
2.1. SR-MPLS
As specified in [RFC8402], an IGP Adjacency Segment (Adj-SID) is an
SR segment attached to a unidirectional adjacency or a set of
unidirectional adjacencies. An IGP Prefix Segment (Prefix-SID) is an
SR segment attached to an IGP prefix, which identifies an instruction
to forward the packet along the path computed using the routing
algorithm in the associated topology. An IGP node segment is an IGP-
Prefix segment that identifies a specific router (e.g., a loopback).
As described in [I-D.ietf-spring-segment-routing-central-epe] and
[I-D.ietf-idr-bgpls-segment-routing-epe], BGP PeerAdj SID is used as
an instruction to steer over a local interface towards a specific
peer node in a peering Autonomous System (AS). These types of SIDs
can be extended to represent both topological instructions and the
set of network resources allocated for packet processing following
the instruction. The MPLS instantiation of Segment Routing is
specified in [RFC8660].
A resource-aware Adj-SID represents a subset of the resources (e.g.
bandwidth and the associated buffer/queuing/scheduling resources) of
a given link, thus each resource-aware Adj-SID is associated with its
own set of TE attributes.
For one IGP link, multiple resource-aware Adj-SIDs SHOULD be
allocated, each of which is associated with a subset of the link
resources allocated on the link. For one inter-domain link, multiple
BGP PeerAdj SIDs MAY be allocated, each of which is associated with a
subset of the link resources allocated on the inter-domain link. The
resource-aware Adj-SIDs MAY be associated with a specific network
topology and/or algorithm, so that it is used only for resource-aware
SR paths computed within the topology and/or algorithm.
Note this per-segment resource allocation complies to the SR
paradigm, which avoids introducing per-path state into the network.
Several approaches can be used to partition the link resource, such
as [FLEXE], Layer-2 logical sub-interfaces, dedicated queues, etc.
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The detailed mechanism of link resource partitioning is out of scope
of this document.
A resource-aware Prefix-SID is associated with a network topology
and/or algorithm in which the attached node participates, and in
addition, a resource-aware prefix-SID is associated with a set of
network resources (e.g. bandwidth and the associated buffer/queuing/
scheduling resources) allocated on each node and link participating
in the same topology and/or algorithm. Such set of network resources
can be used for forwarding packets with this resource-aware prefix-
SID along the paths computed in the associated topology and/or
algorithm.
Although it is possible that each resource-aware prefix-SID is
associated with a set of dedicated resources in the network, this
implies the overhead with per-prefix resource reservation in both
control plane signaling and data plane states, and if network
resources are allocated for one prefix on all the possible paths, it
is likely some resources will be wasted. A practical approach is
that a common set of network resources are allocated by each network
node and link participating in a topology and/or algorithm, and are
associated with a group of resource-aware prefix-SIDs of the same
topology and/or algorithm. Such a common set of network resources
constitutes a resource group. For a given <topology, algorithm>
tuple, there can be one or multiple resource groups, the resource
groups which are associated with the same <topology, algorithm> tuple
shares the SPF computation result.
This helps to reduce the dynamics in per-prefix resource allocation
and adjustment, so that the network resource can be allocated based
on planning and does not have to rely on dynamic signaling. While
when the set of nodes and links participate in a <topology,
algorithm> tuple changes, the set of network resources allocated on
specific nodes and links may need to be adjusted. This means that
the resources allocated to resource-aware Adj-SIDs on those links may
have to be adjusted and new TE metrics for the associated Adj-SIDs
re-advertised.
For one IGP prefix, multiple resource-aware prefix-SIDs SHOULD be
allocated. Each resource-aware prefix-SID can be associated with a
unique <topology, algorithm> tuple, in this case different <topology,
algorithm> tuples can be used to distinguish the resource-aware
prefix-SIDs for the same prefix. In another case, for one IGP
prefix, multiple resource-aware prefix-SIDs can be associated with
the same <topology, algorithm> tuple, then an additional
distinguisher needs to be introduced to distinguish different
resource-aware prefix-SIDs associated with the same <topology,
algorithm> but different groups of network resources.
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A group of resource-aware Adj-SID and resource-aware Prefix-SIDs can
be used to construct the SID lists to steer the traffic along the
explicit paths (either strict or loose) and be processed using the
set of network resources identified by the SIDs.
In data packet forwarding, each resource-aware Adj-SID identifies
both the next-hop and the set of resources used for packet processing
on the outgoing interface. Each resource-aware Prefix-SID identifies
a path to the node which the prefix is attached to, and the common
set of network resources used for packet forwarding on network nodes
along the path. The transit nodes determine the next-hop of the
packet and the set of associated local resources based on the
resource-aware prefix-SID, then forward the packet to the next-hop
using the set of local resources.
When the set of network resources allocated on the egress node also
needs to be determined, It is RECOMMENDED that Penultimate Hop
Popping (PHP) [RFC3031] be disabled, or the inner service label is
used to infer the set of resources to be used for packet processing
on the egress node of the SR path.
This mechanism requires to allocate additional prefix-SIDs or adj-
SIDs for network segments to identify different set of network
resources. As the number of resource groups increases, the number of
SIDs would increase accordingly, while it should be noted that there
is no per-path state introduced into the network.
2.2. SRv6
As specified in [I-D.ietf-spring-srv6-network-programming], an SRv6
Segment Identifier (SID) is a 128-bit value which consists of a
locator (LOC) and a function (FUNCT), optionally it may also contain
additional arguments (ARG) immediately after the FUNCT. The Locator
part of the SID is routable and leads to the node which instantiates
that SID, which means the Locator can be parsed by all nodes in the
network. The FUNCT part of the SID is an opaque identification of a
local function bound to the SID, and the ARG bits of the SID can be
used to encode additional information for the processing of the
behavoir bound to the SID. The FUNCT and ARG parts can only be
parsed by the node which instantiates the SRv6 SID.
For one SRv6 node, multiple resource-aware SRv6 LOCs SHOULD be
allocated. A resource-aware LOC is associated with a network
topology and/or algorithm in which the node participates, and in
addition, a resource-aware LOC is associated with a set of local
resources (e.g. bandwidth, processing and storage resources) on each
node participating in the same topology and/or algorithm. Such set
of network resources are used to forward the packets with SIDs which
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has the resource-aware LOC as its prefix, along the path computed
with the associated topology and/or algorithm. Similar to the
resource-aware prefix-SIDs in SR-MPLS, a practical approach is that a
common set of network resources are allocated by each network node
and link participating in a topology and/or algorithm, and are
associated with a group of resource-aware LOC of the same topology
and/or algorithm.
For one IGP link, the resource-aware SRv6 End.X SIDs are used to
identify different set of link resources allocated. Each resource-
aware End.X SID SHOULD use a resource-aware LOC as its prefix. SRv6
SIDs for other types of functions MAY also be assigned as resource-
aware SIDs, which can identify the set of network resources allocated
by the node for executing the function.
A group of resource-aware SRv6 SIDs can be used to construct the SID
lists to steer the traffic along the explicit paths (either strict or
loose) and be processed using the set of network resources identified
by the SRv6 SIDs and Locators.
In data packet forwarding, each resource-aware End.X SID identifies
both the next-hop and the set of resources used for packet processing
on the outgoing interface. Each resource-aware Locator identifies
the path to the node which the Locator is assigned to, and the set of
network resources used for packet forwarding on network nodes along
the path. The transit nodes determine the next-hop of the packet and
the set of associated local resources based on the resource-aware
Locator, then forward the packet to the next-hop using the set of
local resources.
This mechanism requires to allocate additional SRv6 Locators and SIDs
for network segments to identify different set of network resources.
As the number of resource groups increases, the number of SRv6
Locators and SIDs would increase accordingly, while it should be
noted that there is no per-path state introduced into the network.
3. Control Plane Considerations
The mechanism described in this document makes use of a centralized
controller to collect the information about the network
(configuration, state, routing databases, etc.) as well as the
service information (traffic matrix, performance statistics, etc.)
for the planning of network resources based on service requirement.
Then the centralized controller instructs the network nodes to
allocate the network resources and associate the resources with the
resource-aware SIDs. The resource-aware SIDs can be either
explicitly provisioned by the controller, or dynamically allocated by
network nodes then reported to the controller. The controller is
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also responsible for the centralized computation and optimization of
the SR paths with the topology, algorithm and network resource
constraints. The interaction between the controller and the network
nodes can be based on PCEP [RFC5440], Netconf/YANG [RFC6241]
[RFC7950] and BGP-LS [RFC7752]. In some scenarios, extensions to
some of these protocols is needed, which are out of the scope of this
document and will be specified in separate documents. In some cases,
a centralized controller may not be used, but this would complicate
the operations and planning therefore not suggested.
The distributed control plane is complementary to the centralized
controller. A distributed control plane can be used for the
collection and distribution of the network topology and resource
information associated with SIDs among network nodes, then some of
the nodes can distribute the collected information to the centralized
controller. Distributed route computation for services with topology
and/or resource constraints may also be needed on network nodes. The
distributed control plane may be based on [RFC4915], [RFC5120],
[I-D.ietf-lsr-flex-algo] or the combination of some of them with
necessary extensions.
On network nodes, the support for a resource group and the
information to associate packets with that resource group needs to be
advertised in the control plane, so that all nodes have a consistent
view of the resource group. Given that resource management is a
central function, the knowledge of the exact resources provided to a
resource group needs to be known accurately by the relevant central
control components (e.g. PCE) and the network nodes. This may be
done by configuration, alternative protocols, or by advertisements in
the IGP for collection by BGP-LS. If there are related link
advertisements, then consistency must be assured across that set of
advertisements. To advertise its support for a given resource group,
a node would advertise the identifier of the resource group, the
associated topology and algorithm, and potentially a set of TE
metrics representing the common resources allocated to it. The
details will be described in a separate document.
4. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
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5. Security Considerations
The security considerations of segment routing are applicable to this
document.
The Resource-aware SIDs may be used for provisioning of SR paths or
virtual networks to carry traffic with latency as one of the SLA
parameters. By disrupting the latency of such traffic an attack can
be directly targeted at the customer application, or can be targeted
at the network operator by causing them to violate their SLA,
triggering commercial consequences. Dynamic attacks of this sort are
not something that networks have traditionally guarded against, and
networking techniques need to be developed to defend against this
type of attack. By rigorously policing ingress traffic and carefully
provisioning the resources provided to such services, this type of
attack can be prevented. However care needs to be taken when
providing shared resources, and when the network needs to be
reconfigured as part of ongoing maintenance or in response to a
failure.
The details of the underlay network MUST NOT be exposed to third
parties, to prevent attacks aimed at exploiting a shared resource.
6. Contributors
Zhenbin Li
Email: lizhenbin@huawei.com
Zhibo Hu
Email: huzhibo@huawei.com
Joel Halpern
Email: jmh@joelhalpern.com
7. Acknowledgements
The authors would like to thank Mach Chen, Stefano Previdi, Charlie
Perkins, Bruno Decraene, Loa Andersson, Alexander Vainshtein and John
Drake for the valuable discussion and suggestions to this document.
8. References
8.1. Normative References
[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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[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>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
8.2. Informative References
[FLEXE] "Flex Ethernet Implementation Agreement", March 2016,
<http://www.oiforum.com/wp-content/uploads/OIF-FLEXE-
01.0.pdf>.
[I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
S., and J. Dong, "BGP-LS extensions for Segment Routing
BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
segment-routing-epe-19 (work in progress), May 2019.
[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.ietf-spring-segment-routing-central-epe]
Filsfils, C., Previdi, S., Dawra, G., Aries, E., and D.
Afanasiev, "Segment Routing Centralized BGP Egress Peer
Engineering", draft-ietf-spring-segment-routing-central-
epe-10 (work in progress), December 2017.
[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-09 (work in progress),
November 2020.
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[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-28 (work in
progress), December 2020.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
Authors' Addresses
Jie Dong
Huawei Technologies
Email: jie.dong@huawei.com
Stewart Bryant
Futurewei Technologies
Email: stewart.bryant@gmail.com
Takuya Miyasaka
KDDI Corporation
Email: ta-miyasaka@kddi.com
Yongqing Zhu
China Telecom
Email: zhuyq8@chinatelecom.cn
Fengwei Qin
China Mobile
Email: qinfengwei@chinamobile.com
Zhenqiang Li
China Mobile
Email: li_zhenqiang@hotmail.com
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Francois Clad
Cisco Systems
Email: fclad@cisco.com
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