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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references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) == Outdated reference: A later version (-03) exists of draft-droms-dhc-dhcpv6-solmaxrt-update-02 -- Possible downref: Normative reference to a draft: ref. 'SOLMAXRT' Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6man Working Group S. Krishnan 3 Internet-Draft Ericsson 4 Intended status: Standards Track D. Anipko 5 Expires: May 9, 2013 D. Thaler 6 Microsoft 7 November 5, 2012 9 Packet loss resiliency for Router Solicitations 10 draft-ietf-6man-resilient-rs-00 12 Abstract 14 When an interface on a host is initialized, the host transmits Router 15 Solicitations in order to minimize the amount of time it needs to 16 wait until the next unsolicited multicast Router Advertisement is 17 received. In certain scenarios, these router solicitations 18 transmitted by the host might be lost. This document specifies a 19 mechanism for hosts to cope with the loss of the initial Router 20 Solicitations. Furthermore, on some links, unsolicited multicast 21 Router Advertisements are never sent and the mechanism in this 22 document is intended to work even in such scenarios. 24 Status of this Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on May 9, 2013. 41 Copyright Notice 43 Copyright (c) 2012 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 1.1. Conventions used in this document . . . . . . . . . . . . . 3 60 2. Proposed algorithm . . . . . . . . . . . . . . . . . . . . . . 4 61 3. Open Issue . . . . . . . . . . . . . . . . . . . . . . . . . . 4 62 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 63 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 64 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 65 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 7.1. Normative References . . . . . . . . . . . . . . . . . . . 5 67 7.2. Informative References . . . . . . . . . . . . . . . . . . 5 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 70 1. Introduction 72 As specified in [RFC4861], when an interface on a host is 73 initialized, in order to obtain Router Advertisements quickly, a host 74 transmits up to MAX_RTR_SOLICITATIONS (3) Router Solicitation 75 messages, each separated by at least RTR_SOLICITATION_INTERVAL (4) 76 seconds. In certain scenarios, these router solicitations 77 transmitted by the host might be lost. 79 The generic scenario is that the interface on the host comes up 80 before it gets access to a router. Examples include: 82 a. The host is connected to a bridged residential gateway over 83 Ethernet or WiFi. LAN connectivity is achieved at interface 84 initialization, but the upstream WAN connectivity is not active 85 yet. In this case, the host just gives up after the initial RS 86 retransmits. 87 b. Access networks/links that turn off periodic RAs and only send 88 RAs in response to RSs. In this case, if the link between the AP 89 and the host comes up before the link between the AP and the 90 Controller/Router, the host will never be able to connect. 91 c. Links that are not multicast capable. In this case, sending an 92 RA can only be triggered by an RS (as is the case, for instance, 93 on ISATAP [RFC5214] links). 95 Once the initial RSs are lost, the host gives up and assumes that 96 there are no routers on the link as specified in Section 6.3.7 of 97 [RFC4861]. The host will not have any form of Internet connectivity 98 until the next unsolicited multicast Router Advertisement is 99 received. These Router Advertisements are transmitted at most 100 MaxRtrAdvInterval seconds apart (maximum value 1800 seconds). Thus 101 in the worst case scenario a host would be without any connectivity 102 for 30 minutes. In general, the delay may be unacceptable in some 103 scenarios. 105 1.1. Conventions used in this document 107 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 108 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 109 document are to be interpreted as described in [RFC2119]. 111 2. Proposed algorithm 113 To achieve resiliency to packet loss, the host needs to continue 114 retransmitting the Router Solicitations until it receives a Router 115 Advertisement, or until it is willing to accept that no router 116 exists. If the host continues retransmitting the RSs at 117 RTR_SOLICITATION_INTERVAL second intervals, it may cause excessive 118 network traffic if a large number of such hosts exists. To achieve 119 resiliency while keeping the aggregate network traffic low, the host 120 can use some form of exponential backoff algorithm to retransmit the 121 RSs. 123 Hosts complying to this specification MUST use the exponential 124 backoff algorithm for retransmits that is described in Section 14 of 125 [RFC3315] in order to continuously retransmit the Router 126 Solicitations until a Router Advertisement is received. The hosts 127 SHOULD use the following variables as input to the retransmission 128 algorithm: 130 IRT 4 seconds 131 MRT 3600 seconds 132 MRC 0 133 MRD 0 135 The initial value IRT was chosen to be in line with the current 136 retransmission interval (RTR_SOLICITATION_INTERVAL) that is specified 137 by [RFC4861] and the maximum retransmission time MRT was chosen to be 138 in line with the new value of SOL_MAX_RT as specified by [SOLMAXRT]. 139 This is to ensure that the short term behavior of the RSs is similar 140 to what is experienced in current networks, and longer term 141 persistent retransmission behavior trends towards being similar to 142 that of DHCPv6 [RFC3315] [SOLMAXRT]. 144 3. Open Issue 146 When an IPv6-capable host attaches to a network that does not have 147 IPv6 enabled, it transmits 3 (MAX_RTR_SOLICITATIONS) Router 148 Solicitations as specified in [RFC4861]. If it receives no Router 149 Advertisements, it assumes that there are no routers present on the 150 link and it ceases to send further RSs. With the mechanism specified 151 in this document, the host will continue to retransmit RSs 152 indefinitely at the rate of approximately 1 RS per hour. It is 153 unclear how to differentiate between such a network with no IPv6 154 routers and a link where an IPv6 router is temporarily unreachable 155 but could become reachable in the future. 157 4. IANA Considerations 159 This document does not require any IANA actions. 161 5. Security Considerations 163 This document does not present any additional security issues beyond 164 those discussed in [RFC4861]. 166 6. Acknowledgements 168 The author would like to thank Steve Baillargeon, and Erik Kline for 169 their reviews and suggestions that made this document better. 171 7. References 173 7.1. Normative References 175 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 176 Requirement Levels", BCP 14, RFC 2119, March 1997. 178 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 179 and M. Carney, "Dynamic Host Configuration Protocol for 180 IPv6 (DHCPv6)", RFC 3315, July 2003. 182 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 183 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 184 September 2007. 186 [SOLMAXRT] 187 Droms, R., "Modification to Default Value of SOL_MAX_RT", 188 draft-droms-dhc-dhcpv6-solmaxrt-update-02 (work in 189 progress), January 2012. 191 7.2. Informative References 193 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 194 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 195 March 2008. 197 Authors' Addresses 199 Suresh Krishnan 200 Ericsson 201 8400 Decarie Blvd. 202 Town of Mount Royal, QC 203 Canada 205 Phone: +1 514 345 7900 x42871 206 Email: suresh.krishnan@ericsson.com 208 Dmitry Anipko 209 Microsoft 210 One Microsoft Way 211 Redmond, WA 212 USA 214 Phone: +1 425 703 7070 215 Email: danipko@microsoft.com 217 Dave Thaler 218 Microsoft 219 One Microsoft Way 220 Redmond, WA 221 USA 223 Email: dthaler@microsoft.com