LSVR K. Patel Internet-Draft Arrcus, Inc. Intended status: Informational A. Lindem Expires: September 6, 2018 Cisco Systems S. Zandi G. Dawra Linkedin March 5, 2018 Usage and Applicability of Link State Vector Routing in Data Centers draft-keyupate-lsvr-applicability-00.txt Abstract This document discusses the usage and applicability of Link State Vector Routing (LSVR) extensions in the CLOS architecture of Data Center Networks. The document is intended to provide a simplified guide for the deployment of LSVR extensions. 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 September 6, 2018. Copyright Notice Copyright (c) 2018 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 Patel, et al. Expires September 6, 2018 [Page 1] Internet-Draft March 2018 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. Requirements Language . . . . . . . . . . . . . . . . . . . . 2 3. Recommended Reading . . . . . . . . . . . . . . . . . . . . . 2 4. Common Deployment Scenario . . . . . . . . . . . . . . . . . 3 5. Justification for BGP modifications . . . . . . . . . . . . . 3 6. LSVR Applicability to CLOS Networks . . . . . . . . . . . . . 4 6.1. Usage of LSVR SAFI . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. Security Considerations . . . . . . . . . . . . . . . . . . . 5 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 10.1. Normative References . . . . . . . . . . . . . . . . . . 6 10.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction This document complements [I-D.keyupate-lsvr-bgp-spf] by discussing the applicability of the technology in a simple and fairly common deployment scenario, which is described in Section 4. After describing the deployment scenario, Section 5 will describe the reasons for BGP modifications for such deployments. Once the control plane routing protocol requirements are described, Section 6 will cover the LSVR protocol enhancements to BGP to meet these requirements and their applicability to Data Center CLOS networks. 2. 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] only when they appear in all upper case. They may also appear in lower or mixed case as English words, without any normative meaning. 3. Recommended Reading This document assumes knowledge of existing data center networks and data center network topologies [CLOS]. This document also assumes knowledge of data center routing protocols like BGP [RFC4271], BGP- Patel, et al. Expires September 6, 2018 [Page 2] Internet-Draft March 2018 SPF [I-D.keyupate-lsvr-bgp-spf], OSPF [RFC2328], as well as, data center OAM protocols like LLDP [RFC4957] and BFD [RFC5580]. 4. Common Deployment Scenario Within a Data Center, a common network design to interconnect servers is done using the CLOS topology [CLOS]. The CLOS topology is fully non-blocking and the topology is realized using Equal Cost Multipath (ECMP). In a CLOS topology, the minimum number of parallel paths between two servers is determined by the width of a tier-1 stage as shown in the figure 1. The following example illustrates multistage CLOS topology. Tier-1 +-----+ |NODE | +->| 12 |--+ | +-----+ | Tier-2 | | Tier-2 +-----+ | +-----+ | +-----+ +------------>|NODE |--+->|NODE |--+--|NODE |-------------+ | +-----| 9 |--+ | 10 | +--| 11 |-----+ | | | +-----+ +-----+ +-----+ | | | | | | | | +-----+ +-----+ +-----+ | | | +-----+---->|NODE |--+ |NODE | +--|NODE |-----+-----+ | | | | +---| 6 |--+->| 7 |--+--| 8 |---+ | | | | | | | +-----+ | +-----+ | +-----+ | | | | | | | | | | | | | | +-----+ +-----+ | +-----+ | +-----+ +-----+ |NODE | |NODE | Tier-3 +->|NODE |--+ Tier-3 |NODE | |NODE | | 1 | | 2 | | 3 | | 4 | | 5 | +-----+ +-----+ +-----+ +-----+ +-----+ | | | | | | | | A O B O <- Servers -> Z O O O Figure 1: Illustration of the basic CLOS 5. Justification for BGP modifications Many data centers use BGP as a routing protocol to create an overlay as well as an underlay network for their CLOS Topologies to simplify layer-3 routing and operations [RFC7938]. However, BGP is a path- vector routing protocol. Since it does not have a way for creating a topology, it uses hop-by-hop EBGP peering to facilitate hop-by-hop Patel, et al. Expires September 6, 2018 [Page 3] Internet-Draft March 2018 routing for creating underlay network and for resolving any overlay next hops. The hop-by-hop BGP peering paradigm imposes several restrictions within a CLOS. It severely prohibits a deployment of Route Reflectors/Route Controllers as the EBGP peerings are inline with the data path. The BGP best path algorithm is prefix based and it prevents announcements of prefixes to other BGP speakers until the best path decision process is performed for the prefix at each hop. These restrictions significantly delay the overall convergence of the underlay network within a CLOS. The LSVR SPF modifications allow BGP to overcome these limitations. Furthermore, using the BGP-LS NLRI format [RFC7752] allows the LSVR data to be advertised for nodes, links, and prefixes in the BGP routing domain and used for SPF computations. 6. LSVR Applicability to CLOS Networks With the BGP SPF extensions [I-D.keyupate-lsvr-bgp-spf], the BGP best path computation and route computation are replaced with OSPF-like algorithms [RFC2328] both to determine whether an BGP-LS NLRI has changed and needs to be re-advertised and to compute the routing table. These modifications will significantly improve convergence of the underlay while affording the operational benefits of a single routing protocol [RFC7938]. Since every router in the BGP SPF domain will have a complete view of the topology, BGP sessions are not required on every link in the data center fabric as with the hop-by-hop peering model described in [RFC7938]. Rather, protocols such as BFD [RFC5580] can be used to determine the availability links and switches as opposed to requiring a single-hop BGP session on every link in the data centric fabric. Consequently, the BGP session topology can be much sparser than the data center fabric topology itself and can utilize a BGP route reflector hierarchy with the desired level of redundancy. Data center controllers typically require visibility to the BGP topology to compute traffic-engineered paths. These controllers learn the topology and other relevant information via the BGP-LS address family [RFC7752] which is totally independent of the underlay address families (usually IPv4/IPv6 unicast). Furthermore, in traditional BGP underlays, all the BGP routers will need to advertise their BGP-LS information independently. With the BGP SPF extensions, controllers can learn the topology using the same BGP advertisements used to compute the underlay routes. Furthermore, these data center controllers can avail the convergence advantages of the BGP SPF extensions. The placement of controllers can be outside of the forwarding path or within the forwarding path. Patel, et al. Expires September 6, 2018 [Page 4] Internet-Draft March 2018 Alternatively, as each and every router in the BGP SPF domain will have a complete view of the topology, the operator can also choose to configure BGP sessions in hop-by-hop peering model described in [RFC7938] along with BFD [RFC5580]. In doing so, while the hop-by- hop peering model lacks inherent benefits of the controller-based model, BGP updates need not be serialized by BGP best path algorithm in either of these models. This helps overall network convergence. 6.1. Usage of LSVR SAFI The BGP SPF extensions [I-D.keyupate-lsvr-bgp-spf] define a new BGP- LS SAFI for announcement of BGP SPF link-state. The NLRI format and its associated attributes follow the format of BGP-LS for node, link, and prefix announcements. Whether the peering model within a CLOS follows hop-by-hop peering described in [RFC7938] or any controller- based or route-reflector peering, an operator can exchange BGP SPF SAFI routes over the BGP peering by simply configuring BGP SPF SAFI between the necessary BGP speakers. The BGP-LS SPF SAFI can also co-exist with BGP IP Unicast SAFI which could exchange overlapping IP routes. The routes received by these SAFIs are evaluated, stored, and announced separately according to the rules of [RFC4760]. The tie-breaking of route installation is a matter of the local policies and preferences of the network operator. Finally, as the BGP SPF peering is done following the procedures described in [RFC4271], all the existing transport security mechanisms including [RFC5925] are available for the BGP-LS SPF SAFI. 7. IANA Considerations No IANA updates are requested by this document. 8. Security Considerations This document introduces no new security considerations above and beyond those already specified in the [RFC4271] and [I-D.keyupate-lsvr-bgp-spf]. 9. Acknowledgements The authors would like to thank Alvaro Retana and Yan Filyurin for the review and comments. Patel, et al. Expires September 6, 2018 [Page 5] Internet-Draft March 2018 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, . 10.2. Informative References [CLOS] "A Study of Non-Blocking Switching Networks", The Bell System Technical Journal, Vol. 32(2), DOI 10.1002/j.1538-7305.1953.tb01433.x, March 1953. [I-D.keyupate-lsvr-bgp-spf] Patel, K., Lindem, A., Zandi, S., and W. Henderickx, "Shortest Path Routing Extensions for BGP Protocol", draft-keyupate-lsvr-bgp-spf-00 (work in progress), March 2018. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . [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, . [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007, . [RFC4957] Krishnan, S., Ed., Montavont, N., Njedjou, E., Veerepalli, S., and A. Yegin, Ed., "Link-Layer Event Notifications for Detecting Network Attachments", RFC 4957, DOI 10.17487/RFC4957, August 2007, . [RFC5580] Tschofenig, H., Ed., Adrangi, F., Jones, M., Lior, A., and B. Aboba, "Carrying Location Objects in RADIUS and Diameter", RFC 5580, DOI 10.17487/RFC5580, August 2009, . Patel, et al. Expires September 6, 2018 [Page 6] Internet-Draft March 2018 [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP Authentication Option", RFC 5925, DOI 10.17487/RFC5925, June 2010, . [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, . [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of BGP for Routing in Large-Scale Data Centers", RFC 7938, DOI 10.17487/RFC7938, August 2016, . Authors' Addresses Keyur Patel Arrcus, Inc. 2077 Gateway Pl San Jose, CA 95110 USA Email: keyur@arrcus.com Acee Lindem Cisco Systems 301 Midenhall Way Cary, NC 95110 USA Email: acee@cisco.com Shawn Zandi Linkedin 222 2nd Street San Francisco, CA 94105 USA Email: szandi@linkedin.com Patel, et al. Expires September 6, 2018 [Page 7] Internet-Draft March 2018 Gaurav Dawra Linkedin 222 2nd Street San Francisco, CA 94105 USA Email: gdawra@linkedin.com Patel, et al. Expires September 6, 2018 [Page 8]