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Tantsura 9 Individual 10 May 2, 2017 12 IS-IS Flooding Reduction in MSDC 13 draft-xu-isis-flooding-reduction-in-msdc-01 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 unneccessary 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 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on November 3, 2017. 47 Copyright Notice 49 Copyright (c) 2017 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 66 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 3. Modifications to Current IS-IS Behaviors . . . . . . . . . . 4 68 3.1. IS-IS Routers as Non-DIS . . . . . . . . . . . . . . . . 4 69 3.2. Controllers as DIS . . . . . . . . . . . . . . . . . . . 5 70 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 71 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 72 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 73 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 74 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 75 7.2. Informative References . . . . . . . . . . . . . . . . . 6 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 78 1. Introduction 80 IS-IS is commonly used as an underlay routing protocol for Massively 81 Scalable Data Center (MSDC) networks where CLOS is the most popular 82 toplogy. For a given IS-IS router within the CLOS topology, it would 83 receive multiple copies of exactly the same LSP from multiple IS-IS 84 neighbors. In addition, two IS-IS neighbors may send each other the 85 same LSP simultaneously. The unnecessary link-state information 86 flooding wastes the precious process resource of IS-IS routers 87 greatly and therefore IS-IS could not scale very well in MSDC 88 networks. 90 To simplify the network management task, centralized controllers are 91 becoming fundamental network elements in most MSDCs. One or more 92 controllers are usually connected to all routers within the MSDC 93 network via a Local Area Network (LAN) which is dedicated for network 94 management purpose (called management LAN), as shown in Figure 1. 96 +----------+ +----------+ 97 |Controller| |Controller| 98 +----+-----+ +-----+----+ 99 |DIS |Candidate DIS 100 | | 101 | | 102 ---+---------+---+----------+-----------+---+---------+-Management LAN 103 | | | | | 104 |Non-DIS |Non-DIS |Non-DIS |Non-DIS |Non-DIS 105 | | | | | 106 | +---+--+ | +---+--+ | 107 | |Router| | |Router| | 108 | *------*- | /*---/--* | 109 | / \ -- | // / \ | 110 | / \ -- | // / \ | 111 | / \ --|// / \ | 112 | / \ /*- / \ | 113 | / \ // | -- / \ | 114 | / \ // | -- / \ | 115 | / /X | -- \ | 116 | / // \ | / -- \ | 117 | / // \ | / -- \ | 118 | / // \ | / -- \ | 119 | / // \ | / -- \ | 120 | / // \ | / -- \ | 121 | / // \ | / -- \ | 122 +-+- //* +\\+-/-+ +---\-++ 123 |Router| |Router| |Router| 124 +------+ +------+ +------+ 126 Figure 1 128 With the assistance of a controller acting as IS-IS Designated 129 Intermediate System (DIS) for the management LAN, IS-IS routers 130 within the MSDC network don't need to exchange any IS-IS Protocl 131 Datagram Units (PDUs) other than Hello packets among them. In order 132 to obtain the full topology information (i.e., the fully synchronized 133 link-state database) of the MSDC's network, these IS-IS routers would 134 exchange the link-state information with the controller being elected 135 as IS-IS DIS for the management LAN instead. 137 To further suppress the flooding of multicast IS-IS PDUs originated 138 from IS-IS routers over the management LAN, IS-IS routers would not 139 send multicast IS-IS Hello packets over the management LAN. 140 Insteads, they just wait for IS-IS Hello packets originated from the 141 controller being elected as IS-IS DIS initially. Once an IS-IS DIS 142 for the management LAN has been discovered, they start to send IS-IS 143 Hello packets directly (as unicasts) to the IS-IS DIS periodically. 145 In addition, IS-IS routers would send IS-IS PDUs to the IS-IS DIS for 146 the management LAN as unicasts as well. In contrast, the controller 147 being elected as IS-IS DIS would send IS-IS PDUs as before. As a 148 result, IS-IS routers would not receive IS-IS PDUs from one another 149 unless these IS-IS PDUs are forwarded as unknown unicasts over the 150 management LAN. Through the above modifications to the current IS-IS 151 router behaviors, the IS-IS flooding is greatly reduced, which is 152 much beneficial to improve the scalability of MSDC networks. 154 1.1. Requirements Language 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 158 document are to be interpreted as described in RFC 2119 [RFC2119]. 160 2. Terminology 162 This memo makes use of the terms defined in [RFC1195]. 164 3. Modifications to Current IS-IS Behaviors 166 3.1. IS-IS Routers as Non-DIS 168 After the bidirectional exchange of IS-IS Hello packets among IS-IS 169 routers, IS-IS routers would originate Link State PDUs (LSPs) 170 accordingly. However, these self-originated LSPs need not to be 171 exchanged directly among them anymore. Instead, these LSPs just need 172 to be sent solely to the controller being elected as IS-IS DIS for 173 the management LAN. 175 To further reduce the flood of multicast IS-IS PDUs over the 176 management LAN, IS-IS routers SHOULD send IS-IS PDUs as unicasts. 177 More specifically, IS-IS routers SHOULD send unicast IS-IS Hello 178 packets periodically to the controller being elected as IS-IS DIS. 179 In other words, IS-IS routers would not send any IS-IS Hello packet 180 over the management LAN until they have found an IS-IS DIS for the 181 management LAN. Note that IS-IS routers SHOULD NOT be elected as IS- 182 IS DIS for the management LAN (This is done by setting the DIS 183 Priority of those IS-IS routers to zero). As a result, IS-IS routers 184 would not see each other over the management LAN. In other word, IS- 185 IS routers would not establish adjacencies with one other. 186 Furthermore, IS-IS routers SHOULD send all the types of IS-IS PDUs to 187 the controller being elected as IS-IS DIS as unicasts as well. 189 To advoid the data traffic from being forwarded across the management 190 LAN, the cost of all IS-IS routers' interfaces to the management LAN 191 SHOULD be set to the maximum value. 193 When a given IS-IS router lost its connection to the management LAN, 194 it SHOULD actively establish adjacency with all of its IS-IS 195 neighbors within the CLOS network. As such, it could obtain the full 196 LSDB of the CLOS network while flooding its self-originated LSPs to 197 the remaining part of the whole CLOS network through these IS-IS 198 neighbor. 200 3.2. Controllers as DIS 202 The controller being elected as IS-IS DIS would send IS-IS PDUs as 203 multicasts or unicasts as before. And it SHOULD accept and process 204 those unicast IS-IS PDUs originated from IS-IS routers. Upon 205 receiving any new LSP from a given IS-IS router, the controller being 206 elected as DIS MUST flood it immediately to the management LAN for 207 two purposes: 1) implicitly acknowledging the receipt of that LSP; 2) 208 synchronizing that LSP to all the other IS-IS routers. 210 Furthermore, to decrease the frequency of advertising Complete 211 Sequence Number PDU (CSNP) on the controller being elected as DIS, 212 it's RECOMMENDED that IS-IS routers SHOULD send an explicit 213 acknowledgement with a Partial Sequence Number PDU (PSNP) upon 214 receiving a new LSP from the controller being elected as DIS. 216 4. Acknowledgements 218 The authors would like to thank Peter Lothberg for his valuable comments 219 and suggestions on this document. 221 5. IANA Considerations 223 TBD. 225 6. Security Considerations 227 TBD. 229 7. References 231 7.1. Normative References 233 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 234 dual environments", RFC 1195, DOI 10.17487/RFC1195, 235 December 1990, . 237 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 238 Requirement Levels", BCP 14, RFC 2119, 239 DOI 10.17487/RFC2119, March 1997, 240 . 242 7.2. Informative References 244 [RFC4136] Pillay-Esnault, P., "OSPF Refresh and Flooding Reduction 245 in Stable Topologies", RFC 4136, DOI 10.17487/RFC4136, 246 July 2005, . 248 Authors' Addresses 250 Xiaohu Xu 251 Huawei 253 Email: xuxiaohu@huawei.com 255 Erik Auerswald 256 fgn GmbH 258 Email: auerswald@fg-networking.de 260 Luyuan Fang 261 ebay 263 Email: lufang@ebay.com 265 Jeff Tantsura 266 Individual 268 Email: jefftant@gmail.com