Introducing Resource Awareness to SR Segments
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This is an older version of an Internet-Draft whose latest revision state is "Active".
|Authors||Jie Dong , Stewart Bryant , Takuya Miyasaka , Yongqing Zhu , Fengwei Qin , Zhenqiang Li , Francois Clad|
|Last updated||2021-02-22 (Latest revision 2021-01-18)|
|RFC stream||Internet Engineering Task Force (IETF)|
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|IESG||IESG state||I-D Exists|
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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- 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 August 26, 2021. Dong, et al. Expires August 26, 2021 [Page 1] Internet-Draft Resource-Aware SR Segments February 2021 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 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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 Dong, et al. Expires August 26, 2021 [Page 2] Internet-Draft Resource-Aware SR Segments February 2021 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 Dong, et al. Expires August 26, 2021 [Page 3] Internet-Draft Resource-Aware SR Segments February 2021 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. Dong, et al. Expires August 26, 2021 [Page 4] Internet-Draft Resource-Aware SR Segments February 2021 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. Dong, et al. Expires August 26, 2021 [Page 5] Internet-Draft Resource-Aware SR Segments February 2021 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 Dong, et al. Expires August 26, 2021 [Page 6] Internet-Draft Resource-Aware SR Segments February 2021 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 Dong, et al. Expires August 26, 2021 [Page 7] Internet-Draft Resource-Aware SR Segments February 2021 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. Dong, et al. Expires August 26, 2021 [Page 8] Internet-Draft Resource-Aware SR Segments February 2021 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: email@example.com Zhibo Hu Email: firstname.lastname@example.org Joel Halpern Email: email@example.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>. Dong, et al. Expires August 26, 2021 [Page 9] Internet-Draft Resource-Aware SR Segments February 2021 [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. Dong, et al. Expires August 26, 2021 [Page 10] Internet-Draft Resource-Aware SR Segments February 2021 [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>. Dong, et al. Expires August 26, 2021 [Page 11] Internet-Draft Resource-Aware SR Segments February 2021 [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: firstname.lastname@example.org Stewart Bryant Futurewei Technologies Email: email@example.com Takuya Miyasaka KDDI Corporation Email: firstname.lastname@example.org Yongqing Zhu China Telecom Email: email@example.com Fengwei Qin China Mobile Email: firstname.lastname@example.org Zhenqiang Li China Mobile Email: email@example.com Dong, et al. Expires August 26, 2021 [Page 12] Internet-Draft Resource-Aware SR Segments February 2021 Francois Clad Cisco Systems Email: firstname.lastname@example.org Dong, et al. Expires August 26, 2021 [Page 13]