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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 Maintenance S. Krishnan 3 Internet-Draft Kaloom 4 Updates: 4861 (if approved) J. Korhonen 5 Intended status: Standards Track Broadcom 6 Expires: January 4, 2018 S. Chakrabarti 7 Ericsson 8 E. Nordmark 9 Arista Networks 10 A. Yourtchenko 11 cisco 12 July 3, 2017 14 Support for adjustable maximum router lifetimes per-link 15 draft-ietf-6man-maxra-03 17 Abstract 19 The neighbor discovery protocol specifies the maximum time allowed 20 between sending unsolicited multicast Router Advertisements from a 21 router interface as well as the maximum router lifetime. It also 22 allows the limits to be overridden by link-layer specific documents. 23 This document allows for overriding these values on a per-link basis. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on January 4, 2018. 42 Copyright Notice 44 Copyright (c) 2017 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 61 3. Relationship between AdvDefaultLifetime and MaxRtrAdvInterval 3 62 4. Updates to RFC4861 . . . . . . . . . . . . . . . . . . . . . 4 63 5. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 4 64 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 65 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 66 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 67 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 9.1. Normative References . . . . . . . . . . . . . . . . . . 5 69 9.2. Informative References . . . . . . . . . . . . . . . . . 5 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 72 1. Introduction 74 IPv6 Neighbor Discovery relies on IP multicast with the expectation 75 to be efficient with respect to available bandwidth and to avoid 76 generating interrupts in the network nodes. On some datalink layers 77 multicast may not be natively supported. On such links any possible 78 reduction of multicast traffic will be highly beneficial. 79 Unfortunately, due to the fixed protocol constants specified in 80 [RFC4861] it is difficult to relax the multicast timers for neighbor 81 discovery. There are already link technology specific clarifications 82 how to tune protocol constants for certain system with the 83 expectation to reduce excess Neighbor Discovery Protocol (NDP) 84 traffic. 3GPP cellular links are one existing example 85 [RFC6459][RFC7066]. 87 This document specifies updates to the IPv6 Neighbor Discovery 88 Protocol [RFC4861] for relaxing the the maximum time allowed between 89 sending unsolicited multicast Router Advertisements (RA) from a 90 router interface as well as for the maximum router lifetime. 92 2. Terminology 94 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 95 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 96 document are to be interpreted as described in [RFC2119]. 98 3. Relationship between AdvDefaultLifetime and MaxRtrAdvInterval 100 MaxRtrAdvInterval is an upper bound on the time between the two 101 successive Router Advertisement messages are sent, therefore one 102 might reason about the relationship between these two values in terms 103 of the ratio K=AdvDefaultLifetime/MaxRtrAdvInterval, which expresses 104 how many Router Advertisements will be guaranteed to be sent before 105 the router lifetime expiry. 107 Assuming unicast Solicited Router Advertisements or a perfectly 108 stable network, on a theoretically perfect link with no losses, it 109 would have been sufficient to have K just above 1 - so that the sent 110 Router Advertisement refreshes the router entry just before it 111 expires. On the real links which allow for some loss, one would need 112 to use K>2 in order to minimize the chances of a single router 113 advertisement loss causing a loss of the router entry. 115 The exact calculation will depend on the packet loss probability. An 116 example: if we take a ballpark value of 1% probability of a packet 117 loss, then K=2 will give 0.01% percent chance of an outage due to a 118 packet loss, K=3 will give 0.0001% chance of an outage, and so forth. 119 To reverse the numbers, with these parameters, K~=1 gives 99% 120 reliability, K~=2 gives 99.99% reliability, and K~=3 gives 99.9999% 121 reliability - the latter should be good enough for a lot of 122 scenarios. 124 In a network with higher packet loss or if the higher reliability is 125 desired, the K might be chosen to be even higher. On the other hand, 126 some of the data link layers provide reliable delivery at layer 2 - 127 so there one might even consider using the "theoretical" value of K 128 just above 1. Since the choice of these two parameters does not 129 impact the interoperability per se, this document does not impose any 130 specific constraints on their values other than providing the 131 guidelines in this section, therefore each individual link can 132 optimize accordingly to its use case. 134 Also AdvDefaultLifetime MUST be set to a value greater than or equal 135 to the selected MaxRtrAdvInterval. Otherwise, a router lifetime is 136 guaranteed to expire before the new Router Advertisement has a chance 137 to be sent, thereby creating an outage. 139 4. Updates to RFC4861 141 This document updates Section 6.2.1. of [RFC4861] to update the 142 following router configuration variables. 144 MaxRtrAdvInterval MUST be no greater than 65535. AdvDefaultLifetime 145 MUST either be zero (the router is not to be used as a default 146 router) or be a value between MaxRtrAdvInterval and 65535. 148 As explained in Section 3, the relationship between MaxRtrAdvInterval 149 and AdvDefaultLifetime must be chosen to take into account the 150 probability of packet loss. 152 5. Host Behavior 154 Legacy hosts on a link with updated routers may have issues with a 155 Router Lifetime of more than 9000 seconds. In the few 156 implementations we have tested with general purpose operating 157 systems, there does not seem to be any issues with setting this field 158 to more than 9000, but there might be implementations that 159 incorrectly (since RFC4861 requires receivers to handle any value) 160 reject such RAs. 162 6. Security Considerations 164 On a link where router advertisements are few and far between, the 165 detrimental effects of a rogue router that sends an unsolicited RA 166 are greatly increased. These rogue RAs can be prevented by using 167 approaches like RA-Guard [RFC6105] and SeND [RFC3971] 169 7. IANA Considerations 171 This document does not require any IANA action. 173 8. Acknowledgements 175 The authors would like to thank the members of the 6man efficient ND 176 design team for their comments that led to the creation of this 177 draft. The authors would also like to thank Lorenzo Colitti, Erik 178 Kline, Jeena Rachel John, Brian Carpenter, Tim Chown and Fernando 179 Gont for their comments and suggestions that improved this document. 181 9. References 182 9.1. Normative References 184 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 185 Requirement Levels", BCP 14, RFC 2119, 186 DOI 10.17487/RFC2119, March 1997, 187 . 189 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 190 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 191 DOI 10.17487/RFC4861, September 2007, 192 . 194 9.2. Informative References 196 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 197 "SEcure Neighbor Discovery (SEND)", RFC 3971, 198 DOI 10.17487/RFC3971, March 2005, 199 . 201 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 202 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 203 DOI 10.17487/RFC6105, February 2011, 204 . 206 [RFC6459] Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen, 207 T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation 208 Partnership Project (3GPP) Evolved Packet System (EPS)", 209 RFC 6459, DOI 10.17487/RFC6459, January 2012, 210 . 212 [RFC7066] Korhonen, J., Ed., Arkko, J., Ed., Savolainen, T., and S. 213 Krishnan, "IPv6 for Third Generation Partnership Project 214 (3GPP) Cellular Hosts", RFC 7066, DOI 10.17487/RFC7066, 215 November 2013, . 217 Authors' Addresses 219 Suresh Krishnan 220 Kaloom 221 335 Rue Peel 222 Montreal, QC 223 Canada 225 Email: suresh@kaloom.com 226 Jouni Korhonen 227 Broadcom 228 Porkkalankatu 24 229 FIN-00180 Helsinki 230 Finland 232 Email: jouni.nospam@gmail.com 234 Samita Chakrabarti 235 Ericsson 236 USA 238 Email: samita.chakrabarti@ericsson.com 240 Erik Nordmark 241 Arista Networks 242 Santa Clara, CA 243 USA 245 Email: nordmark@acm.org 247 Andrew Yourtchenko 248 cisco 249 6b de Kleetlaan 250 Diegem 1831 251 Belgium 253 Email: ayourtch@cisco.com