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Ma 9 Juniper 10 December 21, 2020 12 IS-IS Flooding Reduction in MSDC 13 draft-xu-lsr-isis-flooding-reduction-in-msdc-03 15 Abstract 17 IS-IS is commonly used as an underlay routing protocol for MSDC 18 (Massively Scalable Data Center) networks. For a given IS-IS router 19 within the CLOS topology, it would receive multiple copies of exactly 20 the same LSP from multiple IS-IS neighbors. In addition, two IS-IS 21 neighbors may send each other the same LSP simultaneously. The 22 unnecessary link-state information flooding wastes the precious 23 process resource of IS-IS routers greatly due to the fact that there 24 are too many IS-IS neighbors for each IS-IS router within the CLOS 25 topology. This document proposes some extensions to IS-IS so as to 26 reduce the IS-IS flooding within MSDC networks greatly. The 27 reduction of the IS-IS flooding is much beneficial to improve the 28 scalability of MSDC networks. 30 Requirements Language 32 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 33 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 34 document are to be interpreted as described in RFC 2119 [RFC2119]. 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at https://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on June 24, 2021. 53 Copyright Notice 55 Copyright (c) 2020 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (https://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 71 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 3. Modifications to Current IS-IS Behaviors . . . . . . . . . . 4 73 3.1. IS-IS Routers as Non-DIS . . . . . . . . . . . . . . . . 4 74 3.2. Controllers as DIS . . . . . . . . . . . . . . . . . . . 5 75 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 76 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 77 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 78 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 79 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 80 7.2. Informative References . . . . . . . . . . . . . . . . . 6 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 83 1. Introduction 85 IS-IS is commonly used as an underlay routing protocol for Massively 86 Scalable Data Center (MSDC) networks where CLOS is the most popular 87 topology. For a given IS-IS router within the CLOS topology, it 88 would receive multiple copies of exactly the same LSP from multiple 89 IS-IS neighbors. In addition, two IS-IS neighbors may send each 90 other the same LSP simultaneously. The unnecessary link-state 91 information flooding wastes the precious process resource of IS-IS 92 routers greatly and therefore IS-IS could not scale very well in MSDC 93 networks. 95 To simplify the network management task, centralized controllers are 96 becoming fundamental network elements in most MSDCs. One or more 97 controllers are usually connected to all routers within the MSDC 98 network via a Local Area Network (LAN) which is dedicated for network 99 management purpose (called management LAN), as shown in Figure 1. 101 +----------+ +----------+ 102 |Controller| |Controller| 103 +----+-----+ +-----+----+ 104 |DIS |Candidate DIS 105 | | 106 | | 107 ---+---------+---+----------+-----------+---+---------+-Management LAN 108 | | | | | 109 |Non-DIS |Non-DIS |Non-DIS |Non-DIS |Non-DIS 110 | | | | | 111 | +---+--+ | +---+--+ | 112 | |Router| | |Router| | 113 | *------*- | /*---/--* | 114 | / \ -- | // / \ | 115 | / \ -- | // / \ | 116 | / \ --|// / \ | 117 | / \ /*- / \ | 118 | / \ // | -- / \ | 119 | / \ // | -- / \ | 120 | / /X | -- \ | 121 | / // \ | / -- \ | 122 | / // \ | / -- \ | 123 | / // \ | / -- \ | 124 | / // \ | / -- \ | 125 | / // \ | / -- \ | 126 | / // \ | / -- \ | 127 +-+- //* +\\+-/-+ +---\-++ 128 |Router| |Router| |Router| 129 +------+ +------+ +------+ 131 Figure 1 133 With the assistance of a controller acting as IS-IS Designated 134 Intermediate System (DIS) for the management LAN, IS-IS routers 135 within the MSDC network don't need to exchange any IS-IS Protocol 136 Datagram Units (PDUs) other than Hello packets among them. In order 137 to obtain the full topology information (i.e., the fully synchronized 138 link-state database) of the MSDC's network, these IS-IS routers would 139 exchange the link-state information with the controller being elected 140 as IS-IS DIS for the management LAN instead. 142 To further suppress the flooding of multicast IS-IS PDUs originated 143 from IS-IS routers over the management LAN, IS-IS routers would not 144 send multicast IS-IS Hello packets over the management LAN. Instead, 145 they just wait for IS-IS Hello packets originated from the controller 146 being elected as IS-IS DIS initially. Once an IS-IS DIS for the 147 management LAN has been discovered, they start to send IS-IS Hello 148 packets directly (as unicasts) to the IS-IS DIS periodically. In 149 addition, IS-IS routers would send IS-IS PDUs to the IS-IS DIS for 150 the management LAN as unicasts as well. In contrast, the controller 151 being elected as IS-IS DIS would send IS-IS PDUs as before. As a 152 result, IS-IS routers would not receive IS-IS PDUs from one another 153 unless these IS-IS PDUs are forwarded as unknown unicasts over the 154 management LAN. Through the above modifications to the current IS-IS 155 router behaviors, the IS-IS flooding is greatly reduced, which is 156 much beneficial to improve the scalability of MSDC networks. 158 2. Terminology 160 This memo makes use of the terms defined in [RFC1195]. 162 3. Modifications to Current IS-IS Behaviors 164 3.1. IS-IS Routers as Non-DIS 166 After the bidirectional exchange of IS-IS Hello packets among IS-IS 167 routers, IS-IS routers would originate Link State PDUs (LSPs) 168 accordingly. However, these self-originated LSPs need not to be 169 exchanged directly among them anymore. Instead, these LSPs just need 170 to be sent solely to the controller being elected as IS-IS DIS for 171 the management LAN. 173 To further reduce the flood of multicast IS-IS PDUs over the 174 management LAN, IS-IS routers SHOULD send IS-IS PDUs as unicasts. 175 More specifically, IS-IS routers SHOULD send unicast IS-IS Hello 176 packets periodically to the controller being elected as IS-IS DIS. 177 In other words, IS-IS routers would not send any IS-IS Hello packet 178 over the management LAN until they have found an IS-IS DIS for the 179 management LAN. Note that IS-IS routers SHOULD NOT be elected as IS- 180 IS DIS for the management LAN (This is done by setting the DIS 181 Priority of those IS-IS routers to zero). As a result, IS-IS routers 182 would not see each other over the management LAN. In other word, IS- 183 IS routers would not establish adjacencies with one other. 184 Furthermore, IS-IS routers SHOULD send all the types of IS-IS PDUs to 185 the controller being elected as IS-IS DIS as unicasts as well. 187 To avoid the data traffic from being forwarded across the management 188 LAN, the cost of all IS-IS routers' interfaces to the management LAN 189 SHOULD be set to the maximum value. 191 When a given IS-IS router lost its connection to the management LAN, 192 it SHOULD actively establish adjacency with all of its IS-IS 193 neighbors within the CLOS network. As such, it could obtain the full 194 LSDB of the CLOS network while flooding its self-originated LSPs to 195 the remaining part of the whole CLOS network through these IS-IS 196 neighbor. 198 3.2. Controllers as DIS 200 The controller being elected as IS-IS DIS would send IS-IS PDUs as 201 multicasts or unicasts as before. And it SHOULD accept and process 202 those unicast IS-IS PDUs originated from IS-IS routers. Upon 203 receiving any new LSP from a given IS-IS router, the controller being 204 elected as DIS MUST flood it immediately to the management LAN for 205 two purposes: 1) implicitly acknowledging the receipt of that LSP; 2) 206 synchronizing that LSP to all the other IS-IS routers. 208 Furthermore, to decrease the frequency of advertising Complete 209 Sequence Number PDU (CSNP) on the controller being elected as DIS, 210 it's RECOMMENDED that IS-IS routers SHOULD send an explicit 211 acknowledgement with a Partial Sequence Number PDU (PSNP) upon 212 receiving a new LSP from the controller being elected as DIS. 214 4. Acknowledgements 216 The authors would like to thank Peter Lothberg and Erik Auerswald for 217 his valuable comments and suggestions on this document. 219 5. IANA Considerations 221 TBD. 223 6. Security Considerations 225 TBD. 227 7. References 229 7.1. Normative References 231 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 232 dual environments", RFC 1195, DOI 10.17487/RFC1195, 233 December 1990, . 235 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 236 Requirement Levels", BCP 14, RFC 2119, 237 DOI 10.17487/RFC2119, March 1997, 238 . 240 7.2. Informative References 242 [RFC4136] Pillay-Esnault, P., "OSPF Refresh and Flooding Reduction 243 in Stable Topologies", RFC 4136, DOI 10.17487/RFC4136, 244 July 2005, . 246 Authors' Addresses 248 Xiaohu Xu 249 Alibaba, Inc 251 Email: 13910161692@qq.com 253 Luyuan Fang 254 Expedia, Inc 256 Email: luyuanf@gmail.com 258 Jeff Tantsura 259 Apstra, Inc. 261 Email: jefftant.ietf@gmail.com 263 Shaowen Ma 264 Juniper 266 Email: mashao@juniper.net