IDR S. Sangli Internet-Draft S. Hegde Intended status: Standards Track R. Das Expires: January 10, 2022 Juniper Networks Inc. B. Decraene Orange July 09, 2021 Generic Metric for the AIGP attribute draft-ssangli-idr-bgp-generic-metric-aigp-00 Abstract This document defines extensions to the AIGP attribute to carry Generic Metric sub-types. This is applicable when multiple domains exchange BGP routing information. The extension will aid in intent- based end-to-end path selection. 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 January 10, 2022. 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 Sangli, et al. Expires January 10, 2022 [Page 1] Internet-Draft Generic Metric for AIGP attribute July 2021 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 3. Multiple Metric types . . . . . . . . . . . . . . . . . . . . 4 4. Generic Metric TLV . . . . . . . . . . . . . . . . . . . . . 5 5. Usage of Generic-Metric TLV . . . . . . . . . . . . . . . . . 5 6. Updates to Decision Procedure . . . . . . . . . . . . . . . . 6 7. Use-case: Different Metrics across Domains . . . . . . . . . 7 8. Deployment Considerations . . . . . . . . . . . . . . . . . . 8 9. Backward Compatibility . . . . . . . . . . . . . . . . . . . 9 10. Security Considerations . . . . . . . . . . . . . . . . . . . 9 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 13.1. Normative References . . . . . . . . . . . . . . . . . . 10 13.2. Informative References . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. Introduction Large Networks belonging to an enterprise may consist of nodes in the order of thousands and may span across multiple IGP domains where each domain can run separate IGPs or levels/areas. BGP may be used to interconnect such IGP domains, with one or more IGP domains within an Autonomous System. The enterprise network can have multiple Autonomous Systems and BGP may be employed to provide connectivity between these domains. Furthermore, BGP can be used to provide routing over a large number of such independent administrative domains. The traffic types have evolved over years and operators have resorted to defining different metric types within a IGP domain (ISIS or OSPF) for IGP path computation. An operator may wish for intent-based end- to-end path selection. The intent can be bandwidth or delay for example, and need to select paths across multiple domains satisfying the high-bandwidth or low-delay paths. The intent is expressed as metric types and metric values. Some metrics can be assigned administratively by an operator and they are described in the base ISIS, OSPF specifications. Other metrics, for example, are the Traffic Engineering Default Metric defined in [RFC5305] and [RFC3630], Min Unidirectional delay metric defined in [RFC8570] and [RFC7471]. There may be other metrics such as jitter, reliability, fiscal cost, etc. that an operator may wish to express as the cost of Sangli, et al. Expires January 10, 2022 [Page 2] Internet-Draft Generic Metric for AIGP attribute July 2021 a link. The procedures mentioned in the above specifications describe the IGP path computation within IGP domains. With the advent of 5G applications and Network Slicing applications, an operator may wish to provision end-to-end paths across multiple domains to cater to traffic constraints. This is also known as intent-based inter-domain routing and there are certain architectures being developed as described in [I-D.hegde-spring-seamless-sr-architecture] and [I-D.dskc-bess-bgp-car-problem-statement]. The transport planes as described in [I-D.kaliraj-idr-bgp-classful-transport-planes] and color-based routing as described in [I-D.dskc-bess-bgp-car] describe how end-to-end intent-based paths can be established. The proposal described in this document can be used in conjunction with such architectures. When multiple domains are interconnected via BGP, protocol extensions for advertising best-external path and/or ADDPATH as described in [RFC7911] are employed to take advantage of network connectivity thus providing alternate paths. The color-based routing and Transport Plane routing proposals result in alternate paths for a reaching a destination. During the BGP bestpath computation, the step(e) as per section 9.1.2.2 of [RFC4271], the interior cost of a route as determined via the IGP metric value can be used to break the tie. In a network spanning multiple IGP domains, the AIGP TLV encoded within the AIGP attribute described in [RFC7311] can be used to compute the AIGP-enhanced interior cost to be used in the decision process for selecting the bestpath as documented in section 2 of [RFC7311]. The [RFC7311] specifies how AIGP TLV can carry the accumulated IGP metric value. There is a need to synchronize the metric-type values carried between IGP and BGP in order to avoid operational overhead of translation between them. The existing AIGP TLV carries a TLV type and metric- value where TLV type does not map to IGP metric-types defined in the IGP metric-type registry. Hence there is a need to provide a generic metric template to embed the IGP metric-type values within the AIGP attribute. This document extends the AIGP attribute for carrying Generic-Metric TLV and the well-defined sub metric types. This document also provides procedures for handling Generic-Metric during the BGP bestpath computation. 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 Sangli, et al. Expires January 10, 2022 [Page 3] Internet-Draft Generic Metric for AIGP attribute July 2021 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Multiple Metric types Consider the network as shown in Figure 1. The network has multiple domains. Each domain runs a separate IGP instance. Within each domain iBGP sessions are established between the PE routers. eBGP sessions are established between the Border Routers across domains. An operator wishes to compute end-to-end path optimized for a metric- type delay. Each domain will be enabled to compute the IGP paths based on metric-type delay. Such values should also be propagated to the adjacent domains for effective end-to-end path computation. ------IBGP-----EBGP------IBGP------EBGP------IBGP----- | | | | | | +-------------+ +-------------+ +-------------+ | | | | | | | ASBR1+--+ASBR2 ASBR3+--+ASBR4 | | | . . | | . . | | PE1+ Domain1 | . | Domain2 | . | Domain3 +PE2 | | . . | | . . | | | ASBR5+--+ASBR6 ASBR7+--+ASBR8 | | | | | | | +-------------+ +-------------+ +-------------+ |----ISIS1----| |----ISIS2----| |----ISIS3----| Figure 1: WAN Network The AIGP TLV in the AIGP attribute as specified in [RFC7311] supports the IGP default metric. If all domains use IGP cost as the metric, then one can compute the end-to-end path with shortest IGP cost. However if an operator wishes to compute the end-to-end path with metric other than IGP cost, we need additional extensions to the AIGP attribute for carry the metric-types and metric values. The [I-D.ietf-lsr-flex-algo-bw-con] proposes a generic metric type that can embed multiple metric types within it. It supports both standard metric-types and user-defined metric-types. This document leverages the generic-metric draft and proposes extensions to the AIGP attribute to carry Generic Metric TLV as specified below. Sangli, et al. Expires January 10, 2022 [Page 4] Internet-Draft Generic Metric for AIGP attribute July 2021 4. Generic Metric TLV This document proposes a new TLV : Generic-Metric TLV in the AIGP attribute. This will carry the metric type and metric value used in the network. The format is shown below. 0 1 2 3 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | metric-type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | metric-value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.......................... Figure 2: Generic-Metric TLV Generic-Metric TLV Type (1 octet): Code point to be assigned by IANA Generic-Metric TLV Length (2 octets): 9 or more Generic-Metric TLV Value (9 octets): 2 sub-fields as shown below: 1. metric-type (1 octet): Value from IGP metric-type registry. 2. metric-value (8 octets): Value range (0 - 0xffffffffffffffff) 5. Usage of Generic-Metric TLV When a BGP speaker wishes to generate AIGP attribute with Generic- Metric TLV for a prefix, it MUST perform the following procedures. 1. The procedures specified in [RFC7311] section 3.4 should be followed that describes creation of attribute, modifications by the originator and non-originator of the route. 2. If the difference between the new metric-value and the advertised metric-value is less than the configured threshold, the update MAY be suppressed. If the new metric-value is above the configured threshold, a new BGP update containing the new metric- value SHOULD be advertised. 3. If the domain uses a metric type other than IGP cost for the IGP path computation, the BGP speaker MAY add Generic-Metric TLV to the AIGP attribute before advertising to a neighboring BGP speaker. Sangli, et al. Expires January 10, 2022 [Page 5] Internet-Draft Generic Metric for AIGP attribute July 2021 4. The metric-type sub-field in the Generic-Metric TLV will carry the value indicating the type of the metric as specified in the IGP metric-type registry. 5. The value of the metric or cost to reach the prefix being advertised will be encoded in the metric-value sub-field. This is the cost or the distance to the destination prefix from the advertising BGP speaker which sets itself as the next hop as described in section 3.4 of [RFC7311]. 6. Procedures for defining the cost to reach a next hop for various metric-types is outside the scope of this document. When a BGP speaker wishes to send a BGP update attaching the AIGP attribute, it must validate if that session has been enabled for sending the AIGP attribute as per procedures mentioned in [RFC7311]. When a BGP speaker receives a BGP update that has the AIGP attribute with Generic-Metric TLV it MUST perform the following procedures. 1. It must validate if that session has been enabled to receive the AIGP attribute as per rules mentioned in [RFC7311]. 2. If the BGP speaker does not recognize the Generic-Metric TLV or type of metric encoded in metric-type subfield of the TLV, then the BGP speaker will ignore the Generic-Metric TLV and follow the BGP decision procedure as specified in [RFC7311]. 3. If the metric-type matches with the type of the metric configured on the router, then the metric-value sub-field MUST be used in the AIGP-enhanced interior cost computation as specified in the next section. 4. If the metric-type does not match with the type of the metric configured on the router, then the BGP speaker may translate cost encoded in the metric-value field for computing the AIGP-enhanced interior cost specified in [RFC7311]. A policy may be used to provide the metric translation. 6. Updates to Decision Procedure When a route has the AIGP attribute with Generic-Metric TLV and the metric-type sub-field matches with the type of the metric used in the current domain, the AIGP-enhanced interior cost should be computed as below. Let A be the value of the value of the metric-value sub-field of the Generic-Metric TLV. Sangli, et al. Expires January 10, 2022 [Page 6] Internet-Draft Generic Metric for AIGP attribute July 2021 Let m be the cost to reach the next hop that IGP uses for its path computation as described in [RFC7311]. The AIGP-enhanced interior cost will be A+m as described in [RFC7311]. If the type of the metric used in the domain does not match the metric-type sub-field of the Generic-Metric TLV, the metric-value may be translated to the type of the metric used in the domain. The translated metric value can be zero. The translated metric value MUST be used in the AIGP-enhanced interior cost computation which will be used in the decision process as described in [RFC7311]. 7. Use-case: Different Metrics across Domains +--------------+ | Domain2 | | | ......+ASBR21 ASBR22+.... . | | . +------------+ . | igp-metric | . +--------------+ | Domain1 | . +--------------+ . | Domain4 | | | . . | | | ASBR11+.. ..+ASBR41 | +PE1 | | PE2+ | ASBR12+.. ..+ASBR42 | | | . . | | | IGP-metric | . . | delay-metric | +------------+ . +--------------+ . +--------------+ . | Domain3 | . . | | . ......+ASBR31 ASBR32+.... | | | delay-metric | +--------------+ Figure 3: Different metric across network Each domain is a separate Autonomous System. Within each domain, ASBR and PE form iBGP peering. The IGP within each domain uses domain specific metric. Domain3 and Domain4 use delay as the metric while Domain1 and Domain2 use IGP cost as the metric. ASBRs across domains form eBGP peering. The use-case is to find delay-based end- to-end path from Domain1 to Domain4. Sangli, et al. Expires January 10, 2022 [Page 7] Internet-Draft Generic Metric for AIGP attribute July 2021 This can be achieved by the advertising router to add the AIGP attribute with metric type 1 that represents delay metric. In the above network diagram, ASBR41 (and ASBR42) will advertise prefix PE2-loopback with Generic-Metric TLV with metric-type 1. The metric- value sub-field of the Generic-Metric TLV will represent the cost to reach PE2's loopback end-point from the advertising router as they will do next hop self. In Domain3, when ASRB32 advertises the prefix PE2-loopback within the local domain, it may add cost to the metric-value, the value representing the delay introduced by the DMZ link between ASRB32 to ASBR42. When ASRBR31 advertises the prefix PE2-lookback, it will perform the following procedures. 1. Compute the delay d of the path to reach ASBR32 from which it has chosen the bestpath. 2. Add the above d value to the metric-value sub-field of the Generic-Metric TLV. In Domain2 however, the local metric type IGP cost. The ASBR22 may follow the procedure similar to ASBR32 and add the delay value corresponding to the DMZ link between ASBR22 and ASBR41 before advertising the path internally in Domain2. When ASBR21 computes the AIGP-enhanced interior cost, as mentioned before, it may translate the igp cost to reach ASBR22 and may add the translated value to the delay-metric. In the above network example, the delay cost from ASBR21 to ASBR22 is negligible and hence delay-metric value will be unchanged. The procedures for AIGP-enhanced interior cost computation at ASBR11 (and ASBR12) will follow DMZ delay computation procedure described above. PE1 will have two paths to reach PE2-loopback: P1 via ASBR11 (and domain2) and P2 via ASBR12 (and domain3), each having respective AIGP-enhanced interior cost representing end-to-end delay. The BGP decision process described in [RFC7311] will result in delay optimized end-to-end path for PE2-loopback on PE1 that can be used to resolve the service prefixes. 8. Deployment Considerations It can be noted that a domain may translate the metric-value of the metric-type used in the local domain to the metric-type present in the Generic-Metric TLV. The idea is to propagate the cost of reaching the prefix through the domain while maintaining the metric- type chosen by the originating router and domain. The translation of metric types to the one carried in the AIGP attribute can be done via policy. Definition of such policies and how they can be enforced is Sangli, et al. Expires January 10, 2022 [Page 8] Internet-Draft Generic Metric for AIGP attribute July 2021 outside the scope of this document. In topologies where there is a common router between adjacent domains that do iBGP peering, the Border router can provide the translation. All routers of a domain MUST compute the AIGP-enhanced interior cost as described above to be used during decision process. Within a domain, if one router R1 applies AIGP-enhanced interior cost while R2 does not, it may lead to routing loop unless some sort of tunnelling technology viz MPLS, SRv6, IP, etc. is adopted to reach the next hop. In a network where any tunnelling technology is used, one can incrementally deploy the Generic-Metric functionality. In a network without any tunnelling technology, it is recommended that all routers should support Generic-Metric based AIGP-enhanced interior cost computation. 9. Backward Compatibility When a BGP speaker receives an update with the AIGP attribute it may have Generic-Metric TLV. If the BGP speaker understands the AIGP attribute but does not understand the Generic-Metric TLV, it will process the AIGP attribute as per [RFC7311]. However when it needs to advertise the prefix to its peers it will pass on the AIGP attribute with all the TLVs including the unknown Generic-Metric TLV as per [RFC7311]. If a BGP speaker does not understand the Generic- Metric TLV, it may chose sub-optimal BGP path. 10. Security Considerations This document does not introduce any new security considerations beyond those already specified in [RFC4271], [RFC7311]. 11. IANA Considerations IANA is requested to assign a code point for Generic Metric TLV. The metric-type field refers to the IGP metric-type registry defined in [I-D.ietf-lsr-flex-algo-bw-con] 12. Acknowledgements The authors would like to thank John Scudder and Jeff Haas for careful review and suggestions. 13. References Sangli, et al. Expires January 10, 2022 [Page 9] Internet-Draft Generic Metric for AIGP attribute July 2021 13.1. Normative References [I-D.dskc-bess-bgp-car] Rao, D., Agrawal, S., Filsfils, C., Talaulikar, K., Steinberg, D., Jalil, L., Su, Y., Guichard, J., Patel, K., and H. Wang, "BGP Color-Aware Routing (CAR)", draft-dskc- bess-bgp-car-02 (work in progress), May 2021. [I-D.dskc-bess-bgp-car-problem-statement] Rao, D., Agrawal, S., Filsfils, C., Talaulikar, K., Decraene, B., Steinberg, D., Jalil, L., Guichard, J., Patel, K., and W. Henderickx, "BGP Color-Aware Routing Problem Statement", draft-dskc-bess-bgp-car-problem- statement-03 (work in progress), May 2021. [I-D.hegde-spring-seamless-sr-architecture] Hegde, S., Bowers, C., Xu, X., Gulko, A., Bogdanov, A., Uttaro, J., Jalil, L., Khaddam, M., and A. Alston, "Seamless Segment Routing Architecture", draft-hegde- spring-seamless-sr-architecture-00 (work in progress), February 2021. [I-D.ietf-lsr-flex-algo-bw-con] Hegde, S., J, W. B. A., Shetty, R., Decraene, B., Psenak, P., and T. Li, "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints", draft-ietf-lsr-flex-algo-bw- con-00 (work in progress), May 2021. [I-D.kaliraj-idr-bgp-classful-transport-planes] Vairavakkalai, K., Venkataraman, N., Rajagopalan, B., Mishra, G., Khaddam, M., Xu, X., and R. J. Szarecki, "BGP Classful Transport Planes", draft-kaliraj-idr-bgp- classful-transport-planes-07 (work in progress), February 2021. [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Sangli, et al. Expires January 10, 2022 [Page 10] Internet-Draft Generic Metric for AIGP attribute July 2021 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . 13.2. Informative References [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering (TE) Extensions to OSPF Version 2", RFC 3630, DOI 10.17487/RFC3630, September 2003, . [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, . [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006, . [RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur, "BGP-MPLS IP Virtual Private Network (VPN) Extension for IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006, . [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007, . [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008, . [RFC7311] Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro, "The Accumulated IGP Metric Attribute for BGP", RFC 7311, DOI 10.17487/RFC7311, August 2014, . [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, . Sangli, et al. Expires January 10, 2022 [Page 11] Internet-Draft Generic Metric for AIGP attribute July 2021 [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, "Advertisement of Multiple Paths in BGP", RFC 7911, DOI 10.17487/RFC7911, July 2016, . [RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017, . [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, . Authors' Addresses Srihari Sangli Juniper Networks Inc. Exora Business Park Bangalore, KA 560103 India Email: ssangli@juniper.net Shraddha Hegde Juniper Networks Inc. Exora Business Park Bangalore, KA 560103 India Email: shraddha@juniper.net Reshma Das Juniper Networks Inc. 1133 Innovation Way Sunnyvale, CA 94089 USA Email: dreshma@juniper.net Bruno Decraene Orange France Email: bruno.decraene@orange.com Sangli, et al. Expires January 10, 2022 [Page 12]