Open Shortest Path First Z. Zhang Internet-Draft L. Wang Updates: 2328, 5340 (if approved) Juniper Networks, Inc. Intended status: Standards Track D. Dubois Expires: December 12, 2014 General Dynamics C4S V. Julka T. McMillan L3 Communications, Linkabit June 10, 2014 OSPF Two-part Metric draft-zzhang-ospf-two-part-metric-02.txt Abstract This document specifies an optional extension to the OSPF protocol, to represent the metric on a multi-access network as two parts: the metric from a router to the network, and the metric from the network to the router. The router to router metric would be the sum of the two. Requirements Language 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. 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 http://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 December 12, 2014. Zhang, et al. Expires December 12, 2014 [Page 1] Internet-Draft ospf-two-part-metric June 2014 Copyright Notice Copyright (c) 2014 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 (http://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 2. Proposed Enhancement . . . . . . . . . . . . . . . . . . . . 3 3. Speficications . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Router Interface Parameters . . . . . . . . . . . . . . . 4 3.2. Advertising Network-to-Router metric in OSPFv2 . . . . . 4 3.3. Advertising Network-to-Router metric in OSPFv3 . . . . . 4 3.4. SPF Calculation . . . . . . . . . . . . . . . . . . . . . 6 3.5. Backward Compatibility . . . . . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 7.2. Informative References . . . . . . . . . . . . . . . . . 8 1. Introduction For a broadcast network, a Network LSA is advertised to list all routers on the network, and each router on the network includes a link in its Router LSA to describe its connection to the network. The link in the Router LSA includes a metric but the listed routers in the Network LSA does not include a metric. This is based on the assumption that from a particular router, all others on the same network can be reached with the same metric. With some broadcast networks, different routers can be reached with different metrics. RFC 6845 extends the OSPF protocol with a hybrid interface type for that kind of broadcast networks, with which no Network LSA is used and routers simply includes p2p links to all routers on the same network with individual metrics. Broadcast Zhang, et al. Expires December 12, 2014 [Page 2] Internet-Draft ospf-two-part-metric June 2014 capability is still utilized to optimize database synchronization and adjacency maintenance. That works well for broadcast networks on which metric between different pair of routers are really independent. For example, VPLS networks. With certain types of broadcast networks, further optimization can be made to reduce the size of the Router LSAs and number of updates. Consider a satellite radio network with fixed and mobile ground terminals. All communication go through the satellite. When the mobile terminals move about, their communication capability may change. When OSPF runs over the radio network (routers being or in tandem with the terminals), RFC 6845 hybrid interface can be used, but with the following drawbacks. Consider that one terminal/router moves into an area where communication capability degrades significantly. Through the radio control protocol all other routers determine that the metric to this particular one changed and they all need to update their Router LSAs accordingly. The router in question also determines that its metric to reach all others also changed and it also need to update its Router LSA. Consider that there could be many terminals and many of them can be moving fast and frequently, the number/frequency of updates of those large Router LSAs could become inhibiting. 2. Proposed Enhancement Notice that in the above scenario, when one terminal's communication capability changes, its metric to all other terminals and the metric from all other terminals to it will all change in a similar fashion. Given this, the above problem can be easily addressed by breaking the metric into two parts: the metric to the satellite and the metric from the satellite. The metric from terminal R1 to R2 would be the sum of the metric from R1 to the satellite and the metric from the satellite to R2. Now instead of using the RFC6845 hybrid interface type, the network is just treated as a regular broadcast one. A router on the network no longer needs to list individual metrics to each neighbors in its Router LSA. In case of symmetric metric to/from the satellite, it is represented by the transit link's metric in the Router LSA. In case of asymetric metric, it is rerepresented by a special MT Metric (Section 3). Zhang, et al. Expires December 12, 2014 [Page 3] Internet-Draft ospf-two-part-metric June 2014 With the proposed enhancement, the size of Router LSA will be significantly reduced. In addition, when a router's communication capability changes, only that router needs to update its Router LSA. Note that while the example uses the satellite as the relay point at radio level (layer 2), at layer 3 the satellite does not play any role. It does not need to be running layer 3 protocol at all. Therefore for generality, the metric is abstracted as to/from the "network" rather that specifically to/from the "satellite". 3. Speficications The following protocol specifications are added to or modified from the base OSPF protocol. If an area contains one or more two-part metric networks, then all routers in the area must support the extensions specified here. This document does not currently specify a way to detect a router's capability of supporting this, and relies on operator's due diligence in provisioning. A protocol mechanism may be developer in the future. 3.1. Router Interface Parameters The "Router interface parameters" have the following additions: o Two-part metric: TRUE if the interface connects to a multi-access network that uses two-part metric. o Interface input cost: Link state metric from the network to this router. Defaulted to "Interface output cost". May be configured or dynamically adjusted to a value different from the "Interface output cost". If different from the output cost, it MUST be advertised in addition to the link (output) cost for this interface in the router's Router LSA. 3.2. Advertising Network-to-Router metric in OSPFv2 If a router adds a transit link in its Router LSA for a network that uses two-part metric, it additionally add a stub link, with the metric set to the interface input cost. 3.3. Advertising Network-to-Router metric in OSPFv3 If a router is adjacent to the DR on a link that uses two-part metric, the prefixes associated with the interface are included in the intra-area-prefix-lsa, with Referenced LS Type set to 0x2002, Referenced Link State ID set to the DR's Interface ID for the link, Referenced Advertising Router set to the DR's Router ID, and the metric set to the interface input cost. Zhang, et al. Expires December 12, 2014 [Page 4] Internet-Draft ospf-two-part-metric June 2014 If the router is the DR on the link and has included a transit link for the link in its Router LSA, then for the associated prefixes that it includes in its intra-area-prefix-lsa, the metric is set to the interface input cost. Compared with OSPFv2, the network-to-router costs in OSPFv3 are advertised in intra-area-prefix-lsas while the regular router-to- network costs are advertised in router-lsas. With some events that affect all routers, e.g., a storm cloud degrades the communication capability of all radio terminals of a satellite network, all routers will have to update both their router-lsas and intra-area-prefix- lsas, causing excessive flooding in the network. If the underlying protocol has the capability to calculate all routers' network-to- router costs in a centralized fashion and communicate that information to the DR out of band, then alternatively the DR can advertise all its neighbors' network-to-router costs. That way, when the affect-all event happens, only the DR need to update its intra- area-prefix-lsa, hence reducing the flooding on the network. To do that, for each prefix on the link the DR MAY optionally include multiple prefix entries in the intra-area-prefix-lsa, one for each adjacent neighbor, in addition to the prefix entry that the DR includes per RFC 5340 (called the primary entry in this document). For each of those secondary entries, the fields Referenced LS Type and Referenced Link State ID match those in the primary entry, but the Referenced Advertising Router is set the neighbor's Router ID. Note that in this case the non-DRs MUST NOT advertise their interface input cost for the link. Based on the above encoding scheme, the network-to-router costs can be identified the following way: o Look up the DR's intra-area-prefix-lsa and locate the (primary) prefix entry for the link. It is the first prefix entry whose reference fields match the Network LSA. o The DR's network-to-router cost is the metric in the primary prefix entry. o If there are secondary prefix entries following the primary entry, then those entries will specify the neighbors' network-to-router costs. o Otherwise, for the network-to-router cost of a particular neighbor, look up that neighbor's intra-area-prefix-lsa and locate a prefix whose reference fields match the Network LSA. That neighbor's network-to-router cost is the metric in the found prefix. Zhang, et al. Expires December 12, 2014 [Page 5] Internet-Draft ospf-two-part-metric June 2014 3.4. SPF Calculation During the first stage of shortest-path tree calculation for an area, when a vertex V corresponding to a Network LSA is added to the shortest-path tree and its adjacent vertex W (joined by a link in V's corresponding Network LSA), the cost from V to W, which is W's network-to-router cost, is determined the following way: o For OSPFv2, if vertex W's corresponding Router LSA has both a transit link and stub link for the network, the cost from V to W is the metric in the stub link. Otherwise, the cost is 0. o For OSPFv3, procedures in Section 3.3 may determine the cost from V to W. If not, the cost is 0. During the second stage of the calculation, for OSPVv2 the stub links in Router LSAs are ignored if there is a corresponding transit link. For OSPFv3, prefix entries whose Referenced Advertising Router field is not 0 and does not match the advertising router are ignored, and the metric in a DR's primary prefix entry is considered to be 0. 3.5. Backward Compatibility Due to the change of procedures in the SPF calculation, and modified/ additional prefix entries in intra-area-prefix-lsas for the purpose of encoding network-to-router costs, ALL routers in an area that includes one or more two-part metric networks must support the changes specified in this document. To ensure that, if an area is provisioned to support two-part metric networks, all routers supporting this capability must advertise Router Information (RI) LSA with a newly assigned bit set in Router Informational Capabilities TLV: Bit Capabilities 0-5 Various alreay assigned bits 6 OSPF Two-part Metric [TPM] Upon detecting the presence of a reachable Router LSA without a companion RI LSA that has the bit set, all routers MUST disable the two-part metric functionalities and take the following actions: o If this router advertised network-to-router costs before, remove the stub links in OSPFv2 or secondary prefix entries in OSPFv3 that are used for that purpose, and update the metric in the primary prefix entry to 0. o Recalculate routes w/o considering any network-to-router costs. Zhang, et al. Expires December 12, 2014 [Page 6] Internet-Draft ospf-two-part-metric June 2014 4. IANA Considerations This document requests IANA to assigna a new bit in the Router Informational Capabilities TLV to indicate the capability of supporting two-part metric. 5. Security Considerations This document does not introduce new security risks. 6. Acknowledgements The authors would like to thank Acee Lindem for the idea of advertising the network-to-router cost in the stub links and the comments on the backward compatiblity issue. The authors also want to thank Abhay Roy and Eric Wu for their comments and suggestions. 7. References 7.1. Normative References [I-D.ietf-ospf-mt-ospfv3] Mirtorabi, S. and A. Roy, "Multi-topology routing in OSPFv3 (MT-OSPFv3)", draft-ietf-ospf-mt-ospfv3-03 (work in progress), July 2007. [I-D.ietf-ospf-ospfv3-lsa-extend] Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-03 (work in progress), May 2014. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, June 2007. [RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 4970, July 2007. [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, July 2008. Zhang, et al. Expires December 12, 2014 [Page 7] Internet-Draft ospf-two-part-metric June 2014 [RFC5613] Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D. Yeung, "OSPF Link-Local Signaling", RFC 5613, August 2009. 7.2. Informative References [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast and Point-to-Multipoint Interface Type", RFC 6845, January 2013. Authors' Addresses Jeffrey Zhang Juniper Networks, Inc. 10 Technology Park Drive Westford, MA 01886 EMail: zzhang@juniper.net Lili Wang Juniper Networks, Inc. 10 Technology Park Drive Westford, MA 01886 EMail: liliw@juniper.net David Dubois General Dynamics C4S 400 John Quincy Adams Road Taunton, MA 02780 EMail: dave.dubois@gdc4s.com Vibhor Julka L3 Communications, Linkabit 9890 Towne Centre Drive San Diego, CA 92121 EMail: vibhor.julka@l-3Com.com Zhang, et al. Expires December 12, 2014 [Page 8] Internet-Draft ospf-two-part-metric June 2014 Tom McMillan L3 Communications, Linkabit 9890 Towne Centre Drive San Diego, CA 92121 EMail: tom.mcmillan@l-3com.com Zhang, et al. Expires December 12, 2014 [Page 9]