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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) ** Downref: Normative reference to an Informational RFC: RFC 4925 Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Y. Cui 3 Internet-Draft P. Wu 4 Intended status: Standards Track J. Wu 5 Expires: June 2, 2012 Tsinghua University 6 T. Lemon 7 Nominum, Inc. 8 November 30, 2011 10 DHCPv4 over IPv6 Transport 11 draft-ietf-dhc-dhcpv4-over-ipv6-00 13 Abstract 15 Recently, there are demands arising for IPv4 address allocation under 16 IPv6 environment, especially in IPv6 transition scenarios. This 17 document describes the mechanism to survive DHCPv4 over IPv6 network. 18 DHCPv4 messages are transported in IPv6 packets when traversing the 19 IPv6 network. DHCPv4 protocol behavior of the client and server is 20 extended to support this IPv6 transport. For the relay case, a new 21 suboption of the Relay Agent Information Option is defined to carry 22 the remote IPv6 address of the clients. 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 June 2, 2012. 41 Copyright Notice 43 Copyright (c) 2011 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 2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3 60 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 4. Protocol Summary . . . . . . . . . . . . . . . . . . . . . . . 4 62 5. Client Relay Agent IPv6 Address Sub-option . . . . . . . . . . 6 63 6. Client Relay Agent Behavior . . . . . . . . . . . . . . . . . . 6 64 7. IPv6-Transport Server Behavior . . . . . . . . . . . . . . . . 7 65 8. IPv6-Transport Relay Agent Behavior . . . . . . . . . . . . . . 7 66 9. Security Consideration . . . . . . . . . . . . . . . . . . . . 8 67 10. IANA consideration . . . . . . . . . . . . . . . . . . . . . . 8 68 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 69 11.1. Normative References . . . . . . . . . . . . . . . . . . . 8 70 11.2. Informative References . . . . . . . . . . . . . . . . . . 8 72 1. Introduction 74 DHCPv4 [RFC2131] was not designed with IPv6 consideration. In 75 particular, DHCPv4 cannot work on the IPv6 network. However, with 76 IPv4-IPv6 coexistence coming to reality, the demand of allocating 77 IPv4 address under IPv6 environment naturally arises. To meet this 78 demand, DHCPv4 should be extended to run over the IPv6 network. 80 A typical scenario that probably requires this feature is IPv4-over- 81 IPv6 hub and spoke tunnel [RFC4925]. In this scenario, IPv4-over- 82 IPv6 tunnel is used to provide IPv4 connectivity to end users (hosts 83 or end networks) across an IPv6 network. If the IPv4 addresses of 84 the end users are provisioned by the concentrator side, then the 85 provisioning process should be able to cross the IPv6 network, too. 86 One such tunnel mechanism is demonstrated in 87 [I-D.ietf-softwire-public-4over6]. DHCPv4 over IPv6 would be a 88 generic solution for this scenario. 90 Three main flavours of solutions may be considered: 92 o Use DHCPv6 instead of DHCPv4, to provision IPv4-related 93 connectivity. In DHCPv6, the provisioned IPv4 address can be 94 embedded into IPv6 address, or carried within a new option. Along 95 with that, dedicated options are needed to convey IPv4-related 96 information, such as the IPv4 address of DNS server, NTP server, 97 etc. Therefore it will put a certain amount of IPv6-unrelated 98 information into DHCPv6 protocol. 100 o Use DHCPv4 and tunnel DHCPv4-in-IPv4 packets over IPv6. Unlike 101 the previous approach where DHCPv6 is used for both IPv4 and IPv6 102 connectivity, this approach consists in preserving the separation 103 between IPv4 and IPv6 connectivity information. It allows to 104 maintain the IPv4 service without major modification of IPv6- 105 related provisioning resources, and sustains DHCPv4 to be the 106 IPv4-related information carrier. However, this approach enforces 107 an IPv4-in-IPv6 tunnel onto DHCP, and requires extra efforts to 108 maintain tunnel endpoint information for encapsulation use. 110 o Use DHCPv4 and extend it to work over IPv6 transport. This 111 flavour uses IPv6 directly for DHCP packet transport instead of 112 relying on IPv4-in-IPv6 tunnel, and it keeps the advantage of 113 separation with IPv6 connectivity information. This document 114 focuses on this flavour. The document will define the extensions 115 of DHCPv4 protocol behavior, as well as a new suboption of the 116 Relay Agent Information Option, to fully support DHCPv4 over IPv6. 118 2. Requirements Language 119 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 120 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 121 document are to be interpreted as described in [RFC2119]. 123 3. Terminology 125 This document makes use of the following terms: 127 o DHCPv4: IPv4 Dynamic Host Configuration Protocol [RFC2131]. 129 o Client Relay Agent(CRA): a special DHCPv4 Relay Agent that sits on 130 the same, IPv6-accessable host with the DHCPv4 client. CRA works 131 as a "bridge" between DHCPv4 client and the IPv6 network, to 132 convert between IPv4 transport and IPv6 transport. 134 o IPv6-Transport Server(TSV): a DHCPv4 Server that support supports 135 IPv6 transport. TSV can listen on IPv6 for incoming DHCPv4 136 messages, and send DHCPv4 messages in IPv6 packets. 138 o IPv6-Transport Relay Agent(TRA): a DHCPv4 Relay Agent that 139 supports IPv6 transport. TRA sits on a machine which has both 140 IPv6 and IPv4 connectivity, and relays DHCP packets between CRA 141 and normal DHCPv4 server. 143 o Client Relay Agent IPv6 Address Sub-option(6ADDR suboption): a new 144 suboption of DHCP Relay Agent Information Option [RFC3046] defined 145 in this document. 6ADDR suboption is used by TRA to carry the IPv6 146 address of a CRA. 148 4. Protocol Summary 150 The scenario for DHCPv4 over IPv6 transport is shown in Figure 1. 151 DHCPv4 clients and DHCPv4 server/relay are separated by an IPv6 152 network in the middle. DHCP messages between a client and the 153 server/relay cannot naturally be forwarded to each other because they 154 are by default IPv4 UDP packets, either unicast or broadcast. To 155 bridge this gap, both the client side and the server/relay side 156 should enable DHCPv4 over IPv6 transport. To be more precise, they 157 shoudl support delivering and receiving DHCP messages in IPv6 UDP 158 packets and thereby traverse the IPv6 network. 160 On the client side, a special relay agent called Client Relay Agent 161 is placed on the same machine with the client. CRA is used to relay 162 DHCP messages from the client to the server, and from the server to 163 the client. CRA sends DHCPv4 messages to the server through unicast 164 IPv6 UDP, and receives unicast IPv6 UDP packets with the DHCPv4 165 messages from the server. By using CRA, no extension is required on 166 the DHCP client. 168 +-------------------------+ 169 +------+ | 170 |DHCPv4| | 171 |Client| +-------+ 172 +------+ |DHCPv4 | 173 | IPv6 Network |Server/| 174 +------+ |Relay | 175 |DHCPv4| +-------+ 176 |Client| | 177 +------+ | 178 +-------------------------+ 180 Figure 1 Scenario of DHCPv4 over IPv6 Transport 182 The IPv6-Transport DHCPv4 server can receive DHCP messages delivered 183 in IPv6 UDP from CRA, and send out DHCP messages to CRA using IPv6 184 UDP(figure 2(a)). TSV should send DHCP messages to the IPv6 address 185 from which it receives relevant DHCP messages earlier. 187 When CRAs communicate with an IPv6-Transport Relay Agent rather than 188 with a server directly, the situation will become a little more 189 complicated. Besides the IPv6 communication with CRA, TRA also 190 communicates with a regular DHCPv4 server through IPv4. Therefore, 191 when TRA relays DHCP messages between a CRA and the DHCPv4 server, it 192 receives DHCP message from the CRA in IPv6 and sends it to the server 193 in IPv4, while receives DHCP message from the server in IPv4 and 194 sends it to the CRA in IPv6. TRA has to use the DHCP Relay Agent 195 Information Option(Option 82) to record the IPv6 address of a CRA, 196 which will be used as forwarding destination when relaying DHCP a 197 message from the server. Since Option 82 doesn't has an existing 198 suboption that fits in the case, this document defines a new Client 199 Relay Agent IPv6 Address Sub-option. 201 +------+ +------+ 202 |client| IPv6 network |TSV | 203 |+CRA |----------------| | 204 +------+ +------+ 205 (a)client--server case 207 +------+ +------+ +------+ 208 |client| IPv6 network |TRA | IPv4 network |server| 209 |+CRA |----------------| |--------------| | 210 +------+ +------+ +------+ 211 (b)client--relay--server case 213 Figure 2 Protocol Summary 215 5. Client Relay Agent IPv6 Address Sub-option 217 This suboption MUST be added by a DHCPv4 TRA. It encodes the IPv6 218 address of the host from which a DHCPv4-in-IPv6 CRA-to-TRA packet was 219 received. It is intended for the TRA to relay DHCPv4 replies back to 220 the proper CRA. To be more specific, the TRA uses the IPv6 address 221 encoded in this suboption as the destination IPv6 address when 222 relaying a DHCPv4 reply to IPv6 network. 224 The CRA IPv6 address MUST be unique in the IPv6 domain. 226 The 6ADDR suboption has a fixed length of 18 octets. The SubOpt code 227 is tbd by IANA, the length field should be 16, and the following 16 228 octets contain the CRA IPv6 address. 230 DHCP servers MAY use this suboption to select parameters specific to 231 particular hosts. Servers MAY parse this suboption and extract the 232 semantic of IPv6 address. 234 SubOpt Len Agent Remote ID 235 +------+------+------+------+------+- -+------+ 236 | tbd | 16 | a1 | a2 | a3 | ... | a16 | 237 +------+------+------+------+------+- -+------+ 239 Figure 3 Client Relay Agent IPv6 Address Sub-option format 241 6. Client Relay Agent Behavior 243 A Client Relay Agent sits on the same machine with the DHCPv4 client. 244 CRA is a special type of relay agent, which relays DHCPv4 messages 245 between regular client and TSV/TRA. The communication between CRA 246 and the client happens within the machine using IPv4, and the 247 communication between CRA and TSV/TRA happens on the IPv6 network 248 using IPv6. 250 A CRA is configured with one or more IPv6 addresses of TSV/TRA. This 251 configuration is provided before DHCPv4 process, for example through 252 DHCPv6 option, or by some other mechanisms depending on the 253 application scenarios. 255 A CRA listens for DHCP packets on IPv4 UDP port 67. When it receives 256 from IPv4 any DHCP packet with bootp op field = 1, it forwards the 257 packet using the standard DHCP relay agent format, but over UDPv6, 258 with source port 67 and destination port 67. Here the CRA MUST NOT 259 include an option 82 or modify the giaddr field of the DHCP packet. 260 The CRA forwards the packet to each of the DHCP server or relay agent 261 with which it is configured. The CRA MUST use a global IPv6 address 262 if it has one. 264 A CRA also listens for DHCP packets on IPv6 UDP port 68. When it 265 receives from IPv6 any DHCP packet with bootp op field = 2, the CRA 266 checks to see if the packet contains option 82, and if so, it drops 267 the packet. Otherwise, it delivers the packet to the DHCP client 268 using IPv4. 270 7. IPv6-Transport Server Behavior 272 To support IPv6 transport, the behavior of DHCPv4 server should be 273 extended. The IPv6-Transport Server can listen on IPv6 port 67 for 274 DHCPv4 packets, and send DHCPv4 packets through IPv6. 276 A TSV listens for DHCP packets on IPv6 UDP port 67. When it receives 277 from IPv6 a DHCP packet, it MUST record the IPv6 source address of 278 that packet and retain it as the return address of the packet. That 279 is to say, when sometime later the TSV responds to this packet, it 280 MUST send the reply packet to the IPv6 return address retained 281 earlier. The rest of TSV DHCP process is the same with normal DHCPv4 282 server. A TSV can also listen on IPv4 UDP port 67 like a normal 283 DHCPv4 server, and process normally when receives IPv4 DHCPv4 packet. 285 This document places no new requirements on DHCPv4 servers that do 286 not listen on UDPv6--in order to use an IPv4-only DHCPv4 server 287 through an IPv6 connection, a TRA is required. 289 8. IPv6-Transport Relay Agent Behavior 291 An IPv6-Transport Relay Agent sits between IPv6 network and IPv4 292 network, and relays DHCPv4 message between CRAs and IPv4-only DHCPv4 293 server. The communication between CRAs and the TRA uses IPv6, while 294 the communication between TRA and server uses IPv4. A TRA listens on 295 IPv6 UDP port 67 for DHCP packets with bootp op field = 1, as well as 296 IPv4 UDP port 68 for DHCP packets with bootp op field = 2. 298 When relaying a DHCP message from CRA to server, TRA MUST add an 299 option 82 with a 6ADDR suboption. This suboption contains the IPv6 300 source address of the message (the CRA's IPv6 address) which is 301 retained when the message is received in IPv6. The TRA MUST also 302 store the IPv4 address of itself in the giaddr field of the DHCP 303 message. The TRA MAY include a Link Selection Suboption [RFC3527] to 304 indicate to the DHCP server which link to use when choosing an IP 305 address. 307 When a TRA receives a DHCP message from the DHCP server, if the 308 packet contains no 6ADDR suboption, the TRA discards the packet. 309 Otherwise, it processes it as required by [RFC3046], and forwards it 310 to the IPv6 address recorded in the 6ADDR suboption. 312 9. Security Consideration 314 This specification raises no particular security issues to the DHCPv4 315 protocol model. 317 10. IANA consideration 319 IANA is requested to assign one new suboption code from the registry 320 of DHCP Agent Sub-Option Codes maintained in 321 http://www.iana.org/assignments/bootp-dhcp-parameters. This 322 suboption code will be assigned to the Client Relay Agent IPv6 323 Address Sub-option. 325 11. References 327 11.1. Normative References 329 [RFC2119] Bradner, S., "Key words for use in 330 RFCs to Indicate Requirement 331 Levels", BCP 14, RFC 2119, 332 March 1997. 334 [RFC2131] Droms, R., "Dynamic Host 335 Configuration Protocol", RFC 2131, 336 March 1997. 338 [RFC3046] Patrick, M., "DHCP Relay Agent 339 Information Option", RFC 3046, 340 January 2001. 342 [RFC3527] Kinnear, K., Stapp, M., Johnson, 343 R., and J. Kumarasamy, "Link 344 Selection sub-option for the Relay 345 Agent Information Option for 346 DHCPv4", RFC 3527, April 2003. 348 [RFC4925] Li, X., Dawkins, S., Ward, D., and 349 A. Durand, "Softwire Problem 350 Statement", RFC 4925, July 2007. 352 11.2. Informative References 354 [I-D.ietf-softwire-public-4over6] Cui, Y., Wu, J., Wu, P., Metz, C., 355 Vautrin, O., and Y. Lee, "Public 356 IPv4 over Access IPv6 Network", dr 357 aft-ietf-softwire-public-4over6-00 358 (work in progress), 359 September 2011. 361 Authors' Addresses 363 Yong Cui 364 Tsinghua University 365 Department of Computer Science, Tsinghua University 366 Beijing 100084 367 P.R.China 369 Phone: +86-10-6260-3059 370 EMail: cuiyong@tsinghua.edu.cn 372 Peng Wu 373 Tsinghua University 374 Department of Computer Science, Tsinghua University 375 Beijing 100084 376 P.R.China 378 Phone: +86-10-6278-5822 379 EMail: peng-wu@foxmail.com 381 Jianping Wu 382 Tsinghua University 383 Department of Computer Science, Tsinghua University 384 Beijing 100084 385 P.R.China 387 Phone: +86-10-6278-5983 388 EMail: jianping@cernet.edu.cn 390 Ted Lemon 391 Nominum, Inc. 392 2000 Seaport Blvd 393 Redwood City 94063 394 USA 396 Phone: +1-650-381-6000 397 EMail: mellon@nominum.com