LSR Working Group A. Wang Internet-Draft China Telecom Intended status: Standards Track A. Lindem Expires: February 28, 2020 Cisco Systems J. Dong Huawei Technologies P. Psenak K. Talaulikar Cisco Systems August 27, 2019 OSPF Extension for Prefix Originator draft-ietf-lsr-ospf-prefix-originator-03 Abstract This document describes Open Shortest Path First (OSPF) v2 and OSPFv3 encodings to advertise the router-id of the originator of inter-area prefixes for OSPFv2 and OSPFv3 Link-State Advertisement (LSA), which are needed in several use cases in multi-area OSPF use cases. 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 February 28, 2020. Copyright Notice Copyright (c) 2019 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 Wang, et al. Expires February 28, 2020 [Page 1] Internet-Draft OSPF Prefix Originator August 2019 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 2. Conventions used in this document . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Conventions used in this document . . . . . . . . . . . . . . 4 5. Scenario Description . . . . . . . . . . . . . . . . . . . . 4 6. Prefix Source Router-ID sub-TLV . . . . . . . . . . . . . . . 5 7. Extended LSA Elements of Procedure . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 11.1. Normative References . . . . . . . . . . . . . . . . . . 7 11.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Inter-Area Topology Retrieval Process . . . . . . . 9 Appendix B. Special Considerations on Inter-Area Topology Retrieval . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction [I-D.ietf-ospf-mpls-elc] defines mechanisms to Entropy Readable Label Depth (ERLD) for ingress Label Switching Router (LSR) to discover each LSR's capability of performing Entropy Label (EL) -based load- balancing in Multi Protocol Label Switch (MPLS) networks. The ingress LSR can use this information to push the appropriate label stack for specific traffic, especially in segment routing environments and other stacked LSPs scenarios. However, in inter-area scenarios, the Area Border Router (ABR) does not advertise the originating OSPF router-id for inter-area prefixes. An OSPF router in one area doesn't know where the prefixes really came from and can't determine the router that originated inter-area prefixes and then can't judge the ERLD capabilities of the destination. It is necessary to transfer the originator information of these inter-area prefixes to ensure the ingress LSR constructs the right label stack. More generally, [RFC8476] defines a mechanism to advertise multiple types of supported Maximum SID Depths (MSD) at node and/or link granularity. This information will be referred when the head-end Wang, et al. Expires February 28, 2020 [Page 2] Internet-Draft OSPF Prefix Originator August 2019 router starts to send traffic to destination prefixes. In inter-area scenario, it is also necessary for the sender to learn the capabilities of the receivers associated with the inter-area prefixes. There is also another scenario where knowing the originator of inter- area prefixes is useful. For example, Border Gateway Protocol Link- State (BGP-LS) [RFC7752] describes mechanisms using the BGP protocol to advertise Link-State information. This can enable an Software Definition Network (SDN) controller to collect the underlay network topology automatically. But if the underlay network is divided into multiple areas and running the OSPF protocol, it is not easy for the SDN controller to rebuild the multi-area topology, because normally an ABR that connects multiple areas will hide the detailed topology information for these non-backbone areas. If only the internal routers within backbone area run the BGP-LS protocol, they just learn and report the summary network information from the non-backbone areas. If the SDN controller can learn the originator of the inter-area prefixes, it is possible to rebuild the inter-area topology automatically. [RFC7794] introduces the Intermediate System to Intermediate System (IS-IS) "IPv4/IPv6 Source Router IDs" Type-Length-Value (TLV) to advertise the source of the prefixes redistributed from a different IS-IS level. This TLV can be used in the above scenarios. Such solution can also be applied in networks that run the OSPF protocol, but the related LSAs TLV must be extended. This draft provides such solution for the OSPFv2 and OSPFv3 protocols. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] . 3. Terminology The following terms are used in this document: o ABR: Area Border Router o ERLD: Entropy Readable Label Depth o EL: Entropy Label Wang, et al. Expires February 28, 2020 [Page 3] Internet-Draft OSPF Prefix Originator August 2019 o IS-IS: Intermediate System to Intermediate System o LSA: Link-State Advertisement o MSD: Maximum SID Depths o NLRI: Network Layer Reachability Information o OSPF: Open Shortest Path First o SID: Segment IDentifier o SDN: Software Definition Network 4. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] . 5. Scenario Description Figure 1 illustrates the topology scenario when OSPF is running in multi-area. R0-R4 are routers in backbone area, S1-S4,T1-T4 are internal routers in area 1 and area 2 respectively. R1 and R3 are area border routers between area 0 and area 1. R2 and R4 are area border routers between area 0 and area 2. N1 is the network between router S1 and S2 and N2 is the network between router T1 and T2. Ls1 is the loopback address of Node S1 and Lt1 is the loopback address of Node T1. Wang, et al. Expires February 28, 2020 [Page 4] Internet-Draft OSPF Prefix Originator August 2019 +-----------------+ |IP SDN Controller| +--------+--------+ | | BGP-LS | +---------------------+------+--------+-----+--------------+ | +--+ +--+ ++-+ ++-+ +-++ + -+ +--+| | |S1+--------+S2+---+R1+---|R0+----+R2+---+T1+--------+T2|| | +-++ N1 +-++ ++-+ +--+ +-++ ++++ N2 +-++| | | | | | || | | | | | | | || | | | +-++ +-++ ++-+ +-++ ++++ +-++| | |S4+--------+S3+---+R3+-----------+R4+---+T3+--------+T4|| | +--+ +--+ ++-+ +-++ ++-+ +--+| | | | | | | | | | Area 1 | Area 0 | Area 2 | +---------------------+---------------+--------------------+ Figure 1: OSPF Inter-Area Prefix Originator Scenario If S1 wants to send traffic to prefix Lt1 that is connected T1 in another area, it should know the ERLD, and MSD values that are associated with the node T1, and then construct the right label stack at the ingress node for the target traffic. In another scenario, If R0 has some method to learn the originator of network N1 and reports such information to IP SDN controller, then it is possible for the controller to retrieval the topology in non- backbone area. The topology retrieval process and its usage limitation are described in the Appendix A and Appendix B . From the above scenarios, we can conclude it is useful to introduce and define the prefix originator sub TLV within OSPF. 6. Prefix Source Router-ID sub-TLV [RFC7684] and [RFC8362] define the TLV extensions for OSPFv2 and OSPFv3 respectively. These documents facilitate addition of new attributes for prefixes. Based on these formats, we can define new sub-TLV to advertise the "Prefix Source Router ID", as that defined in [RFC7794]. The "Prefix Source Router-ID" sub-TLV has the following format: Wang, et al. Expires February 28, 2020 [Page 5] Internet-Draft OSPF Prefix Originator August 2019 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Source Router-ID | +---------------------------------------------------------------+ Figure 2: Prefix Source Router-ID sub-TLV Format o Source Router-ID Sub-TLV Type: TBD1[RFC7684] or TBD2 [RFC8362] o Length: 4 o Value: Router-ID of OSPFv2/OSPFv3 source router For OSPFv2, this sub-TLV is a sub-TLV of OSPFv2 Extended Prefix TLV, which SHOULD be included in the "OSPFv2 Extended Prefix Opaque LSA" . For OSPFv3, this sub-TLV is a sub-TLV of "Inter-Area-Prefix TLV", which SHOULD be included in the "E-Inter-Area-Prefix-LSA". 7. Extended LSA Elements of Procedure When an ABR, for example R2 in Figure 1, receives the Router-LSA announcement in area 2, it should originate the corresponding "OSPFv2 Extended Prefix Opaque LSA" for OSPFv2 or "E-Inter-Area-Prefix-LSA" for OSPFv3 that includes the Source Router-ID sub-TLV for the network prefixes, e.g., for prefix Lt1, N2. etc., which identifies the source router that advertised the prefix. When S1 in another area receives such LSA, it then can learn that prefix Lt1 is associated with node T1, check the ERLD, or MSD value according to its necessity, and construct the right label stack at the ingress node S1 for the traffic destined to Lt1. When R0 receives such LSA, it learns the Prefix Source Router-id and includes it in the prefix information advertised to an SDN controller as described in[I-D.ietf-idr-bgp-ls-segment-routing-ext]. The SDN controller can then use such information to build the inter-area topology according to the process described in the Appendix A. The topology retrieval process may not suitable for some environments as stated in Appendix B. 8. Security Considerations Security concerns for OSPF are addressed in [RFC5709] Wang, et al. Expires February 28, 2020 [Page 6] Internet-Draft OSPF Prefix Originator August 2019 Advertisement of the additional information defined in this document introduces no new security concerns 9. IANA Considerations This specification defines one Prefix Source Router-ID sub-TLV as described in Section 6. This value should be added to the existing "OSPFv2 Extended Prefix TLV Sub-TLVs" registry and "OSPFv3 Extended- LSA Sub-TLVs registry" respectively. The following new sub-TLV is added to the registry of "OSPFv2 Extended Prefix TLV Sub-TLVs". The allocation policy is IETF Review that defined in [RFC7684] +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ | Code Point | Description | Status | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ | TBD | Prefix Source Sub-TLV | Allocation from IANA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ Figure 3: CodePoint in "OSPFv2 Extended Prefix TLV Sub-TLVs" The following new sub-TLV is added to the registry of "OSPFv3 Extended-LSA Sub-TLVs". The allocation policy is IETF Review that defined in [RFC8362] +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ | Code Point | Description | Status | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ | TBD | Prefix Source Sub-TLV | Allocation from IANA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ Figure 4: CodePoint in "OSPFv3 Extended-LSA Sub-TLVs" 10. Acknowledgement Many thanks to Les Ginsberg for his valuable suggestions on this draft. And also thanks Jeff Tantsura,Rob Shakir, Van De Velde Gunter, Goethals Dirk, Shaofu Peng, John E Drake for their valuable comments on this draft. 11. References 11.1. 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, . Wang, et al. Expires February 28, 2020 [Page 7] Internet-Draft OSPF Prefix Originator August 2019 [RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M., Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic Authentication", RFC 5709, DOI 10.17487/RFC5709, October 2009, . [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 2015, . [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, . [RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4 and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794, March 2016, . [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and F. Baker, "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 2018, . [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, DOI 10.17487/RFC8476, December 2018, . 11.2. Informative References [I-D.ietf-idr-bgp-ls-segment-routing-ext] Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., and M. Chen, "BGP Link-State extensions for Segment Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16 (work in progress), June 2019. [I-D.ietf-ospf-mpls-elc] Xu, X., Kini, S., Psenak, P., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Entropy Readable Label-stack Depth Using OSPF", draft-ietf-ospf- mpls-elc-08 (work in progress), May 2019. Wang, et al. Expires February 28, 2020 [Page 8] Internet-Draft OSPF Prefix Originator August 2019 Appendix A. Inter-Area Topology Retrieval Process When an IP SDN Controller receives this information, it should compare the prefix Network Layer Reachability Information (NLRI) that included in the BGP-LS packet. When it encounters the same prefix but with different source router ID, it should extract the corresponding area-ID, rebuild the link between these two different source routers in non-backbone area. Belows is one example that based on the Figure 1: Assuming we want to rebuild the connection between router S1 and router S2 that locates in area 1: a. Normally, router S1 will advertise prefix N1 within its router- LSA. b. When this router-LSA reaches the ABR router R1, it will convert it into summary-LSA, add the Prefix Source Router-ID sub-TLV, which is router id of S1 in this example. c. R1 then floods this extension summary-LSA to R0, which is running BGP-LS protocol with IP SDN Controller. The controller then knows the prefixes of N1 is from S1. d. Router S2 will do the similar process, and the controller will also learn that prefixes N1 is also from S2. e. Then it can reconstruct the link between S1 and S2, using the prefix N1. The topology within Area 1 can then be reconstructed accordingly. Iterating the above process continuously, the IP SDN controller can retrieve a detailed topology that spans multiple areas. Appendix B. Special Considerations on Inter-Area Topology Retrieval The above topology retrieval process can be applied in the case where each link between routers is assigned a unique prefix. However, there are some situations where this heuristic cannot be applied. Specifically, the cases where the link is unnumbered or the prefix corresponding to the link is an anycast prefix. The Appendix A heuristic to rebuild the topology can normally be used if all links are numbered. For anycast prefixes, if it corresponds to the loopback interface and has a host prefix length, i.e., 32 for IPv4 prefixes and 128 for IPv6 prefixes, Appendix A can also apply. Wang, et al. Expires February 28, 2020 [Page 9] Internet-Draft OSPF Prefix Originator August 2019 Authors' Addresses Aijun Wang China Telecom Beiqijia Town, Changping District Beijing 102209 China Email: wangaj3@chinatelecom.cn Acee Lindem Cisco Systems 301 Midenhall Way Cary, NC 27513 USA Email: acee@cisco.com Jie Dong Huawei Technologies Beijing China Email: jie.dong@huawei.com Peter Psenak Cisco Systems Pribinova Street 10 Bratislava, Eurovea Centre, Central 3 81109 Slovakia Email: ppsenak@cisco.com Ketan Talaulikar Cisco Systems S.No. 154/6, Phase I, Hinjawadi Pune 411 057 India Email: ketant@cisco.com Wang, et al. Expires February 28, 2020 [Page 10]