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Droms 3 Internet-Draft Cisco Systems 4 Updates: 3315 (if approved) August 3, 2012 5 Intended status: Standards Track 6 Expires: February 4, 2013 8 Modification to Default Value of SOL_MAX_RT 9 draft-droms-dhc-dhcpv6-solmaxrt-update-03 11 Abstract 13 This document updates RFC 3315 by redefining the default value for 14 SOL_MAX_RT and defining an option through which a DHCPv6 server can 15 override the client's default value for SOL_MAX_RT with a new value. 17 Status of this Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on February 4, 2013. 34 Copyright Notice 36 Copyright (c) 2012 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 1. Introduction 51 Section 5.5 of the DHCPv6 specification [RFC3315] defines the default 52 value of SOL_MAX_RT to be 120 seconds. In some circumstances, this 53 default will lead to an unacceptably high volume of aggregated 54 traffic at a DHCPv6 server. 56 The change to SOL_MAX_RT is in response to DHCPv6 message rates 57 observed at a DHCPv6 server in a deployment in which many DHCPv6 58 clients are sending Solicit messages but the DHCPv6 server has been 59 configured not to respond to those Solicit messages. 61 1.1. Requirements Language 63 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 64 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 65 document are to be interpreted as described in RFC 2119 [RFC2119]. 67 2. Update to RFC 3315 69 This document changes section 5.5 of RFC 3315 [RFC3315] as follows: 71 OLD: 72 SOL_MAX_RT 120 secs Max Solicit timeout value 74 NEW: 75 SOL_MAX_RT 3600 secs Max Solicit timeout value 77 With this change, a DHCPv6 client that does not receive a 78 satisfactory response will send Solicit messages with the same 79 initial frequency and exponential backoff as specified in section 80 17.1.2 of RFC 3315 [RFC3315]. However, the long term behavior of 81 these DHCPv6 clients will be to send a Solicit message every 3600 82 seconds rather than every 120 seconds, significantly reducing the 83 aggregated traffic at the DHCPv6 server. 85 3. SOL_MAX_RT option 87 A DHCPv6 server sends the SOL_MAX_RT option to a client to override 88 the default value of SOL_MAX_RT. The value of SOL_MAX_RT in the 89 option replaces the default value defined in RFC 3315 [RFC3315]. One 90 use for the SOL_MAX_RT option is to set a longer value for 91 SOL_MAX_RT, which reduces the Solicit traffic from a client that has 92 not received a response to its Solicit messages. 94 The format of the SOL_MAX_RT option is: 96 0 1 2 3 97 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 98 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 99 | option-code | option-len | 100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 101 | SOL_MAX_RT value | 102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 104 option-code OPTION_SOL_MAX_RT (TBD). 106 option-len 4. 108 SOL_MAX_RT value Overriding value for SOL_MAX_RT in seconds. 110 Figure 1 112 A DHCPv6 client MUST include the SOL_MAX_RT option code in an Option 113 Request option [RFC3315] in any message it sends. 115 The DHCPv6 server MAY include the SOL_MAX_RT option in any response 116 it sends to a client that has included the SOL_MAX_RT option code in 117 an Option Request option. The SOL_MAX_RT option is sent in the main 118 body of the message to client, not as a sub-option in, e.g., an 119 IA_NA, IA_TA [RFC3315] or IA_PD [RFC3633] option. 121 If a DHCPv6 client receives a message containing a SOL_MAX_RT option, 122 the client MUST set its internal SOL_MAX_RT parameter to the value 123 contained in the SOL_MAX_RT option. As a result of receiving this 124 option, the DHCPv6 client MUST NOT send any Solicit messages more 125 frequently than allowed by the retransmission mechanism defined in 126 sections 17.1.2 and 14 of RFC 3315 [RFC3315]. 128 4. Updates to RFC 3315 130 RFC 3315 [RFC3315], section 17.1.3: 132 OLD: 134 The client MUST ignore any Advertise message that includes a Status 135 Code option containing the value NoAddrsAvail, with the exception 136 that the client MAY display the associated status message to the 137 user. 139 NEW: 141 The client MUST ignore any Advertise message that includes a Status 142 Code option containing the value NoAddrsAvail, with the exception 143 that the client MUST process an included SOL_MAX_RT option and MAY 144 display the associated status message to the user. 146 Figure 2 148 RFC 3315 [RFC3315], section 17.2.2: 150 OLD: 152 If the server will not assign any addresses to any IAs in a 153 subsequent Request from the client, the server MUST send an 154 Advertise message to the client that includes only a Status Code 155 option with code NoAddrsAvail and a status message for the user, a 156 Server Identifier option with the server's DUID, and a Client 157 Identifier option with the client's DUID. 159 NEW: 161 If the server will not assign any addresses to any IAs in a 162 subsequent Request from the client, the server MUST send an 163 Advertise message to the client that includes only a Status Code 164 option with code NoAddrsAvail and a status message for the user, a 165 Server Identifier option with the server's DUID, a Client 166 Identifier option with the client's DUID and (optionally) a 167 SOL_MAX_RT option. 169 Figure 3 171 5. Security Considerations 173 This document introduces one security consideration beyond those 174 described in RFC 3315 [RFC3315]. A malicious DHCPv6 server might 175 cause a client to set its SOL_MAX_RT parameter to an arbitrarily high 176 value with the SOL_MAX_RT option. Assuming the client also receives 177 a response from a valid DHCPv6 server, the large value for SOL_MAX_RT 178 will not have any effect. 180 6. IANA Considerations 182 IANA is requested to assign an option code from the "DHCP Option 183 Codes" Registry for OPTION_SOL_MAX_RT. 185 7. Normative References 187 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 188 Requirement Levels", BCP 14, RFC 2119, March 1997. 190 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 191 and M. Carney, "Dynamic Host Configuration Protocol for 192 IPv6 (DHCPv6)", RFC 3315, July 2003. 194 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 195 Host Configuration Protocol (DHCP) version 6", RFC 3633, 196 December 2003. 198 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 199 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 200 September 2007. 202 Author's Address 204 Ralph Droms 205 Cisco Systems 206 1414 Massachusetts Avenue 207 Boxborough, MA 01719 208 USA 210 Phone: +1 978 936 1674 211 Email: rdroms@cisco.com