Network Working Group X. Xu Internet-Draft Alibaba Inc Intended status: Standards Track L. Fang Expires: October 19, 2018 Expedia, Inc J. Tantsura Nuage Networks S. Ma Juniper April 17, 2018 IS-IS Flooding Reduction in MSDC draft-xu-lsr-isis-flooding-reduction-in-msdc-00 Abstract IS-IS is commonly used as an underlay routing protocol for MSDC (Massively Scalable Data Center) networks. For a given IS-IS router within the CLOS topology, it would receive multiple copies of exactly the same LSP from multiple IS-IS neighbors. In addition, two IS-IS neighbors may send each other the same LSP simultaneously. The unneccessary link-state information flooding wastes the precious process resource of IS-IS routers greatly due to the fact that there are too many IS-IS neighbors for each IS-IS router within the CLOS topology. This document proposes some extensions to IS-IS so as to reduce the IS-IS flooding within MSDC networks greatly. The reduction of the IS-IS flooding is much beneficial to improve the scalability of MSDC networks. 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 RFC 2119 [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 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 Xu, et al. Expires October 19, 2018 [Page 1] Internet-Draft April 2018 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 October 19, 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 (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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Modifications to Current IS-IS Behaviors . . . . . . . . . . 4 3.1. IS-IS Routers as Non-DIS . . . . . . . . . . . . . . . . 4 3.2. Controllers as DIS . . . . . . . . . . . . . . . . . . . 5 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction IS-IS is commonly used as an underlay routing protocol for Massively Scalable Data Center (MSDC) networks where CLOS is the most popular toplogy. For a given IS-IS router within the CLOS topology, it would receive multiple copies of exactly the same LSP from multiple IS-IS neighbors. In addition, two IS-IS neighbors may send each other the same LSP simultaneously. The unnecessary link-state information flooding wastes the precious process resource of IS-IS routers greatly and therefore IS-IS could not scale very well in MSDC networks. Xu, et al. Expires October 19, 2018 [Page 2] Internet-Draft April 2018 To simplify the network management task, centralized controllers are becoming fundamental network elements in most MSDCs. One or more controllers are usually connected to all routers within the MSDC network via a Local Area Network (LAN) which is dedicated for network management purpose (called management LAN), as shown in Figure 1. +----------+ +----------+ |Controller| |Controller| +----+-----+ +-----+----+ |DIS |Candidate DIS | | | | ---+---------+---+----------+-----------+---+---------+-Management LAN | | | | | |Non-DIS |Non-DIS |Non-DIS |Non-DIS |Non-DIS | | | | | | +---+--+ | +---+--+ | | |Router| | |Router| | | *------*- | /*---/--* | | / \ -- | // / \ | | / \ -- | // / \ | | / \ --|// / \ | | / \ /*- / \ | | / \ // | -- / \ | | / \ // | -- / \ | | / /X | -- \ | | / // \ | / -- \ | | / // \ | / -- \ | | / // \ | / -- \ | | / // \ | / -- \ | | / // \ | / -- \ | | / // \ | / -- \ | +-+- //* +\\+-/-+ +---\-++ |Router| |Router| |Router| +------+ +------+ +------+ Figure 1 With the assistance of a controller acting as IS-IS Designated Intermediate System (DIS) for the management LAN, IS-IS routers within the MSDC network don't need to exchange any IS-IS Protocl Datagram Units (PDUs) other than Hello packets among them. In order to obtain the full topology information (i.e., the fully synchronized link-state database) of the MSDC's network, these IS-IS routers would exchange the link-state information with the controller being elected as IS-IS DIS for the management LAN instead. Xu, et al. Expires October 19, 2018 [Page 3] Internet-Draft April 2018 To further suppress the flooding of multicast IS-IS PDUs originated from IS-IS routers over the management LAN, IS-IS routers would not send multicast IS-IS Hello packets over the management LAN. Insteads, they just wait for IS-IS Hello packets originated from the controller being elected as IS-IS DIS initially. Once an IS-IS DIS for the management LAN has been discovered, they start to send IS-IS Hello packets directly (as unicasts) to the IS-IS DIS periodically. In addition, IS-IS routers would send IS-IS PDUs to the IS-IS DIS for the management LAN as unicasts as well. In contrast, the controller being elected as IS-IS DIS would send IS-IS PDUs as before. As a result, IS-IS routers would not receive IS-IS PDUs from one another unless these IS-IS PDUs are forwarded as unknown unicasts over the management LAN. Through the above modifications to the current IS-IS router behaviors, the IS-IS flooding is greatly reduced, which is much beneficial to improve the scalability of MSDC networks. 2. Terminology This memo makes use of the terms defined in [RFC1195]. 3. Modifications to Current IS-IS Behaviors 3.1. IS-IS Routers as Non-DIS After the bidirectional exchange of IS-IS Hello packets among IS-IS routers, IS-IS routers would originate Link State PDUs (LSPs) accordingly. However, these self-originated LSPs need not to be exchanged directly among them anymore. Instead, these LSPs just need to be sent solely to the controller being elected as IS-IS DIS for the management LAN. To further reduce the flood of multicast IS-IS PDUs over the management LAN, IS-IS routers SHOULD send IS-IS PDUs as unicasts. More specifically, IS-IS routers SHOULD send unicast IS-IS Hello packets periodically to the controller being elected as IS-IS DIS. In other words, IS-IS routers would not send any IS-IS Hello packet over the management LAN until they have found an IS-IS DIS for the management LAN. Note that IS-IS routers SHOULD NOT be elected as IS- IS DIS for the management LAN (This is done by setting the DIS Priority of those IS-IS routers to zero). As a result, IS-IS routers would not see each other over the management LAN. In other word, IS- IS routers would not establish adjacencies with one other. Furthermore, IS-IS routers SHOULD send all the types of IS-IS PDUs to the controller being elected as IS-IS DIS as unicasts as well. To advoid the data traffic from being forwarded across the management LAN, the cost of all IS-IS routers' interfaces to the management LAN SHOULD be set to the maximum value. Xu, et al. Expires October 19, 2018 [Page 4] Internet-Draft April 2018 When a given IS-IS router lost its connection to the management LAN, it SHOULD actively establish adjacency with all of its IS-IS neighbors within the CLOS network. As such, it could obtain the full LSDB of the CLOS network while flooding its self-originated LSPs to the remaining part of the whole CLOS network through these IS-IS neighbor. 3.2. Controllers as DIS The controller being elected as IS-IS DIS would send IS-IS PDUs as multicasts or unicasts as before. And it SHOULD accept and process those unicast IS-IS PDUs originated from IS-IS routers. Upon receiving any new LSP from a given IS-IS router, the controller being elected as DIS MUST flood it immediately to the management LAN for two purposes: 1) implicitly acknowledging the receipt of that LSP; 2) synchronizing that LSP to all the other IS-IS routers. Furthermore, to decrease the frequency of advertising Complete Sequence Number PDU (CSNP) on the controller being elected as DIS, it's RECOMMENDED that IS-IS routers SHOULD send an explicit acknowledgement with a Partial Sequence Number PDU (PSNP) upon receiving a new LSP from the controller being elected as DIS. 4. Acknowledgements The authors would like to thank Peter Lothberg and Erik Auerswald for his valuable comments and suggestions on this document. 5. IANA Considerations TBD. 6. Security Considerations TBD. 7. References 7.1. Normative References [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, DOI 10.17487/RFC1195, December 1990, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Xu, et al. Expires October 19, 2018 [Page 5] Internet-Draft April 2018 7.2. Informative References [RFC4136] Pillay-Esnault, P., "OSPF Refresh and Flooding Reduction in Stable Topologies", RFC 4136, DOI 10.17487/RFC4136, July 2005, . Authors' Addresses Xiaohu Xu Alibaba Inc Email: xiaohu.xxh@alibaba-inc.com Luyuan Fang Expedia, Inc Email: luyuanf@gmail.com Jeff Tantsura Nuage Networks Email: jefftant@gmail.com Shaowen Ma Juniper Email: mashao@juniper.net Xu, et al. Expires October 19, 2018 [Page 6]