OSPF K. Patel Internet-Draft Arrcus Updates: 2328 (if approved) P. Pillay-Esnault Intended status: Standards Track Huawei Technologies Expires: November 20, 2019 M. Bhardwaj S. Bayraktar Cisco Systems May 19, 2019 Host Router Support for OSPFv2 draft-ietf-ospf-ospfv2-hbit-07 Abstract The OSPFv2 specifies an SPF algorithm that identifies transit vertices based on their adjacencies. Therefore, OSPFv2 does not have a mechanism to prevent traffic transiting a participating node if it is a transit vertex in the only existing or shortest path to the destination. The use of metrics to make the node undesirable can only help to repel traffic if an alternative better route exists. This document defines the Host-bit functionality to prevent other OSPFv2 routers from using the router for transit traffic in OSPFv2 routing domains. This document updates the [RFC2328] by assigning a new bit (Host-bit) in the OSPF Router-LSA bit registry. If the Host- bit is set, the calculation of the shortest-path tree for an area, as described in [RFC2328], is modified by including a new check to verify that transit vertices have the Host-bit clear. 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 November 20, 2019. Patel, et al. Expires November 20, 2019 [Page 1] Internet-Draft May 2019 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 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. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 3. Host-bit Support . . . . . . . . . . . . . . . . . . . . . . 3 4. SPF Modifications . . . . . . . . . . . . . . . . . . . . . . 5 5. Auto Discovery and Backward Compatibility . . . . . . . . . . 6 6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 10.1. Normative References . . . . . . . . . . . . . . . . . . 7 10.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction The OSPFv2 specifies an SPF algorithm that identifies transit vertices based on their adjacencies. Therefore, OSPFv2 does not have a mechanism to prevent traffic transiting a participating node if it Patel, et al. Expires November 20, 2019 [Page 2] Internet-Draft May 2019 is a transit vertex in the only existing or shortest path to the destination. The use of metrics to make the node undesirable can only help to repel traffic if an alternative better route exists. This functionality is particularly useful for a number of use cases: 1. To isolate a router to avoid blackhole scenarios when there is a reload and possible long reconvergence times. 2. Closet Switches are usually not used for transit traffic but need to participate in the topology. 3. Overloaded routers could use such a capability to repel traffic until they stabilize. 4. BGP Route reflectors known as virtual Route Reflectors (vRRs), that are not in the forwarding path but are in central locations such as data centers. Such Route Reflectors typically are used for route distribution and are not capable of forwarding transit traffic. However, they need to learn the OSPF topology to perform spf computation for optimal routes and reachbility resolution for its clients [I-D.ietf-idr-bgp-optimal-route-reflection]. This document defines the Host-bit (H-Bit)functionality to prevent other OSPFv2 routers from using the router for transit traffic in OSPFv2 routing domains. This document updates the [RFC2328] by - assigning the Host-bit in the OSPF Router-LSA bit registry - if the host-bit is set then the calculation of the shortest-path tree for an area, as described in section 16.1 of [RFC2328], is modified by including a new check to verify that transit vertices DO NOT have the host-bit set. 2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Host-bit Support This document defines a new router-LSA bit known as the Host Bit or the H-bit. An OSPFv2 router advertising a router-LSA with the H-bit set indicates to other OSPFv2 routers in the area supporting the functionality that it MUST NOT be used as a transit router (see section 4). Patel, et al. Expires November 20, 2019 [Page 3] Internet-Draft May 2019 If the host-bit is NOT set routers MUST act transit routers as described in [RFC2328] ensuring backward compatibility. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |H|0|0|N|W|V|E|B| 0 | # links | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | # TOS | metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TOS | 0 | TOS metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | Host Bit in router-LSA 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |H|0|0|N|W|V|E|B| +-+-+-+-+-+-+-+-+ Host Bit Bit H is the high-order bit of the OSPF as shown above. When set, an OSPFv2 router is a non-transit router and is incapable of forwarding transit traffic. Patel, et al. Expires November 20, 2019 [Page 4] Internet-Draft May 2019 An OSPFv2 router originating a router-LSA with the H-bit set MUST advertise all its router links with a link cost of MaxLinkMetric [RFC6987]. This is to increase the applicability of the H-bit to partial deployments where it is the responsibility of the operator to ensure that OSPFv2 routers not supporting the H-bit do not install routes causing routing loops. When the H-bit is set, an Area Border Router (ABR) MUST advertise a consistent H-bit setting in its self-originated router-LSAs for all attached areas. ONLY IPv4 prefixes associated with its local interfaces MAY be advertised in summary LSAs. When the H-bit is set cannot act as an AS Boundary Router (ASBR), as non-local IPv4 prefixes, e.g., those exported from other routing protocols, MUST NOT be advertised in AS-external-LSAs. 4. SPF Modifications The SPF calculation described in section 16.1 [RFC2328] will be modified to ensure that the routers originating router-LSAs with the H-bit set will not be used for transit traffic. Step 2 is modified as follows: 2) Call the vertex just added to the tree vertex V. Examine the LSA associated with vertex V. This is a lookup in the Area A's link state database based on the Vertex ID. If this is a router-LSA, and the H-bit of the router-LSA is set, and vertex V is not the root, then the router should not be used for transit and step (3) should be executed immediately. If this is a router-LSA, and bit V of the router-LSA (see Section A.4.2) is set, set Area A's TransitCapability to TRUE. In any case, each link described by the LSA gives the cost to an adjacent vertex. For each described link, (say it joins vertex V to vertex W): Patel, et al. Expires November 20, 2019 [Page 5] Internet-Draft May 2019 5. Auto Discovery and Backward Compatibility To avoid the possibility of any routing loops due to partial deployment, this document defines a OSPF Router Information (RI) LSA with a Router Functional Capability TLV that includes the following Router Functional Capability Bit: Bit Capabilities 7 Host Router Support capability Auto Discovery via announcement of the Host Support Functional Capability ensures that the H-bit functionality and its associated SPF changes SHOULD only take effect if all the routers in a given OSPF area support this functionality. Implementations are encouraged to provide a configuration parameter to manually override enforcement of the H-bit functionality in partial deployments where the topology guarantees that OSPFv2 routers not supporting the H-bit do not compute routes resulting in routing loops. More precisely, the advertisement of MaxLinkMetric for the router's non-local links will prevent OSPFv2 routers not supporting the H-bit from attempting to use it for transit traffic. 6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics When calculating the path to an OSPF AS-External-LSA or NSSA-LSA with a Type-2 metric, the advertised Type-2 metric is taken as more significant than the OSPF intra-area or inter-area path. Hence, advertising the links with MaxLinkMetric as specified in [RFC6987] does not discourage transit traffic when calculating AS external or NSSA routes. Consequently, OSPF routers implementing [RFC6987] or this specification should advertise a Type-2 metric of LSInfinity for any self-originated AS-External-LSAs or NSSA-LSAs in situations when the OSPF router is acting as a stub router [RFC6987] or implementing this specification. 7. IANA Considerations IANA is requested to create the OSPF Router-LSA bit registry with the following assignments: Patel, et al. Expires November 20, 2019 [Page 6] Internet-Draft May 2019 Value Description Reference 0x01 Area Border Router (B-bit) [RFC2328] 0x02 AS Boundary Router (E-bit) [RFC2328] 0x04 Virtual Link Endpoint (V-bit) [RFC2328] 0x08 Historic (W-bit) [RFC1584] 0x10 Unconditional NSSA Translator (Nt-bit) [RFC3101] 0x20 Unassigned 0x40 Unassigned 0x80 Host (H-bit) This Document This document also defines a new Router Functional Capability [RFC7770] known as the Host Router Support Functional Capability. This document requests IANA to allocate the value of this capability from the Router Functional Capability Bits TLV. 8. Security Considerations This document introduces no new security considerations beyond those already specified in [RFC6987], [RFC2328], and [RFC5340]. 9. Acknowledgements The authors would like to acknowledge Hasmit Grover for discovery of the limitation in [RFC6987], Acee Lindem, Abhay Roy, David Ward, Burjiz Pithawala and Michael Barnes for their comments. 10. References 10.1. 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, . [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . [RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", RFC 3101, DOI 10.17487/RFC3101, January 2003, . [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, . Patel, et al. Expires November 20, 2019 [Page 7] Internet-Draft May 2019 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, February 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 10.2. Informative References [I-D.ietf-idr-bgp-optimal-route-reflection] Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K. Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft- ietf-idr-bgp-optimal-route-reflection-18 (work in progress), April 2019. [RFC1584] Moy, J., "Multicast Extensions to OSPF", RFC 1584, DOI 10.17487/RFC1584, March 1994, . [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. McPherson, "OSPF Stub Router Advertisement", RFC 6987, DOI 10.17487/RFC6987, September 2013, . Authors' Addresses Keyur Patel Arrcus Email: keyur@arrcus.com Padma Pillay-Esnault Huawei Technologies 2330 Central Expressway Santa Clara, CA 95050 USA Email: padma@huawei.com Patel, et al. Expires November 20, 2019 [Page 8] Internet-Draft May 2019 Manish Bhardwaj Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA Email: manbhard@cisco.com Serpil Bayraktar Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA Email: serpil@cisco.com Patel, et al. Expires November 20, 2019 [Page 9]