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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 (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DHC Working Group P. Kurapati 3 Internet-Draft Juniper Networks Ltd. 4 Updates: 4388 (if approved) R. Desetti 5 Expires: April 11, 2011 B. Joshi 6 Infosys Technologies Ltd. 7 October 8, 2010 9 DHCPv4 lease query by Relay Agent Remote ID 10 draft-ietf-dhc-leasequery-by-remote-id-07.txt 12 Abstract 14 Some Relay Agents extract lease information from the DHCP messages 15 exchanged between the client and DHCP server. This lease information 16 is used by relay agents for various purposes like antispoofing and 17 prevention of flooding. RFC 4388 defines a mechanism for relay 18 agents to retrieve the lease information from the DHCP server as and 19 when this information is lost. The existing lease query mechanism is 20 data driven, which means that a relay agent can initiate the lease 21 query only when it starts receiving data from/to the clients. In 22 certain scenarios, this model is not scalable. This document first 23 looks at issues in existing mechanism and then proposes a new query 24 type, query by Remote ID, to address these issues. 26 Status of this Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on April 11, 2011. 43 Copyright Notice 45 Copyright (c) 2010 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 This document may contain material from IETF Documents or IETF 59 Contributions published or made publicly available before November 60 10, 2008. The person(s) controlling the copyright in some of this 61 material may not have granted the IETF Trust the right to allow 62 modifications of such material outside the IETF Standards Process. 63 Without obtaining an adequate license from the person(s) controlling 64 the copyright in such materials, this document may not be modified 65 outside the IETF Standards Process, and derivative works of it may 66 not be created outside the IETF Standards Process, except to format 67 it for publication as an RFC or to translate it into languages other 68 than English. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 73 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 74 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 8 75 4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 9 76 4.1. Sending the DHCPLEASEQUERY Message . . . . . . . . . . . . 9 77 4.2. Responding to the DHCPLEASEQUERY Message . . . . . . . . . 10 78 4.3. Building a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message . . 10 79 4.4. Determining the IP address to be used in response . . . . 11 80 4.5. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message . . 11 81 4.6. Receiving a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN 82 Message . . . . . . . . . . . . . . . . . . . . . . . . . 11 83 4.7. Receiving No Response to the DHCPLEASEQUERY Message . . . 12 84 4.8. Lease Binding Data Storage Requirements . . . . . . . . . 12 85 4.9. Using the DHCPLEASEQUERY Message with Multiple DHCP 86 Servers . . . . . . . . . . . . . . . . . . . . . . . . . 12 87 5. RFC 4388 Considerations . . . . . . . . . . . . . . . . . . . 13 88 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 89 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 90 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 91 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 92 9.1. Normative Reference . . . . . . . . . . . . . . . . . . . 17 93 9.2. Informative Reference . . . . . . . . . . . . . . . . . . 17 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 96 1. Introduction 98 DHCP relay agents snoop DHCP messages and append a relay agent 99 information option before relaying them to the configured DHCP 100 Server. In this process, some relay agents also glean the lease 101 information sent by the server and maintain this locally. This 102 information is used to prevent spoofing attempts from clients and 103 also sometimes to install routing information. When a relay agent 104 reboots, this information is lost. RFC 4388 [RFC4388] has defined a 105 mechanism to retrieve this lease information from the DHCP server. 106 The existing query types defined by RFC 4388 [RFC4388] are data- 107 driven. When a client sends data upstream, the relay agent can query 108 the server about the related lease information, based on the source 109 MAC/IP address. These mechanisms do not scale well when there are 110 thousands of clients connected to the relay agent. In the data- 111 driven model, lease query does not provide the full and consolidated 112 active lease informations associated with a given connection/circuit, 113 which will result in inefficient anti-spoofing. The relay agent also 114 has to contend with considerable resources for negative caching 115 specially under spoofing attacks. 117 We need a mechanism for a relay agent to retrieve the consolidated 118 lease information for a given connection/circuit before upstream 119 traffic is sent by the clients. 121 +--------+ 122 | DHCP | +--------------+ 123 | Server |-...-| DSLAM | 124 | | | Relay Agent | 125 +--------+ +--------------+ 126 | | 127 +------+ +------+ 128 |Modem1| |Modem2| 129 +------+ +------+ 130 | | | 131 +-----+ +-----+ +-----+ 132 |Node1| |Node2| |Node3| 133 +-----+ +-----+ +-----+ 135 Figure 1 137 For example, when a DSLAM acting as a Relay Agent is rebooted, it 138 should query the server for the lease information for all the 139 connections/circuits. Also, as shown in the above figure, there 140 could be multiple clients on one DSL circuit. The relay agent should 141 get the lease information of all the clients connected to a DSL 142 circuit. This is possible by introducing a new query type based on 143 the Remote ID sub-option of the Relay Agent Information option. This 144 document talks about the motivation for the new query type and the 145 method to perform it. 147 2. Terminology 149 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 150 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 151 document are to be interpreted as described in RFC 2119 [RFC2119]. 153 This document uses the following terms: 155 o "Access Concentrator" 157 An access concentrator is a router or switch at the broadband access 158 provider's edge of a public broadband access network. This document 159 assumes that the access concentrator includes the DHCP relay agent 160 functionality. 162 o "DHCP client" 164 A DHCP client is an Internet node using DHCP to obtain configuration 165 parameters such as a network address. 167 o "DHCP relay agent" 169 A DHCP relay agent is a third-party agent that transfers Bootstrap 170 Protocol (BOOTP) and DHCP messages between clients and servers 171 residing on different subnets, per RFC 951 [RFC951] and RFC 1542 172 [RFC1542]. 174 o "DHCP server" 176 A DHCP server is an Internet node that returns configuration 177 parameters to DHCP clients. 179 o "Fast path" 181 Data transfer that happens through a Network Processor or an ASIC, 182 which are programmed to forward the data at very high speeds. 184 o "Gleaning" 186 Gleaning is the extraction of location information from DHCP 187 messages, as the messages are forwarded by the DHCP relay agent 188 function. 190 o "Location information" 192 Location information is information needed by the access concentrator 193 to forward traffic to a broadband-accessible node. This information 194 includes knowledge of the node's hardware address, the port or 195 virtual circuit that leads to the node, and/or the hardware address 196 of the intervening subscriber modem. 198 o "MAC address" 200 In the context of a DHCP packet, a MAC address consists of the 201 following fields: hardware type "htype", hardware length "hlen", and 202 client hardware address "chaddr". 204 o "Slow path" 206 Data transfer that happens through the control plane. Typically this 207 has very limited buffers to store data and the speeds are very low 208 compared to the fast path data transfer. 210 o "Upstream" 212 Upstream is the direction from the broadband subscriber towards the 213 access concentrator. 215 3. Motivation 217 Consider a typical access concentrator (e.g., DSLAM) working also as 218 a DHCP relay agent. A "Fast path" and a "slow path" generally exist 219 in most networking boxes. Fast path processing is done in a network 220 processor or an ASIC (Application Specific Integrated Circuit). Slow 221 path processing is done in a normal processor. As much as possible, 222 regular data forwarding should be done in the fast path. Slow path 223 processing should be reduced as it may become a bottleneck. 225 For an access concentrator having multiple access ports, multiple IP 226 addresses may be assigned using DHCP to a single port and the number 227 of clients on a port may be unknown. The access concentrator may 228 also not know the network portions of the IP addresses that are 229 assigned to its DHCP clients. 231 The access concentrator gleans IP address or other information from 232 DHCP negotiations for antispoofing and other purposes. The 233 antispoofing itself is done in the fast path. The access 234 concentrator keeps track of only one list of IP addresses: list of IP 235 addresses that are assigned by the DHCP servers; upstream traffic 236 from all other IP addresses is dropped. If a client starts its data 237 transfer after its DHCP negotiations have been gleaned by the access 238 concentrator, no legitimate packets will be dropped because of 239 antispoofing. In other words, antispoofing is effective (no 240 legitimate packets are dropped and all spoofed packets are dropped) 241 and efficient (antispoofing is done in the fast path). The intention 242 is to achieve similar effective and efficient antispoofing in the 243 lease query scenario also when an access concentrator loses its 244 gleaned information (for example, because of a reboot). 246 After a deep analysis, we found that the three existing query types 247 supported by RFC 4388 [RFC4388] do not provide effective and 248 efficient antispoofing for the above scenario and a new mechanism is 249 required. 251 The existing query types 253 o necessitate a data-driven approach: the lease queries can only be 254 performed when the access concentrator receives data. This 255 results in increased outage time for clients 257 o results in excessive negative caching, consuming a lot of 258 resources under a spoofing attack 260 o results in antispoofing being done in the slow path instead of the 261 fast path 263 4. Protocol Details 265 This section talks about the protocol details for query by Remote ID. 266 Most of the message handling is similar to RFC 4388 [RFC4388] and 267 this section highlights only the differences. Readers are advised to 268 go through RFC 4388 [RFC4388] before going through this section for 269 complete understanding of the protocol. 271 When used in this document, the unqualified term "DHCPLEASEQUERY" 272 indicates a lease query by Remote ID, unless otherwise specified. 274 RFC 3046 [RFC3046] defines two sub-options for the Relay Agent 275 Information option. Sub-option 1 corresponds to the Circuit ID that 276 identifies the local circuit of the access concentrator. This sub- 277 option is unique to the relay agent. Sub-option 2 corresponds to the 278 Remote ID that identifies the remote node connected to the access 279 concentrator. This is globally unique in the network. 281 This document defines a new query type based on the Remote ID sub- 282 option. Suppose that the access concentrator (e.g., DSLAM) lost the 283 lease information when it was rebooted. When the access concentrator 284 comes up, it initiates (for each connection/circuit) a DHCP lease 285 query by Remote ID as defined in this section. For this query, the 286 requester supplies an option 82 that includes only a Remote ID sub- 287 option in the DHCPLEASEQUERY message. 289 The DHCP server MUST reply with a DHCPLEASEACTIVE message if there is 290 an active lease corresponding to the Remote ID that is present in the 291 DHCPLEASEQUERY message. Otherwise, the server MUST reply with a 292 DHCPLEASEUNKNOWN message. Servers that do not implement DHCP lease 293 query based on Remote ID SHOULD simply not respond. 295 4.1. Sending the DHCPLEASEQUERY Message 297 The DHCPLEASEQUERY message is typically sent by an access 298 concentrator. The DHCPLEASEQUERY message uses the DHCP message 299 format as described in RFC 2131 [RFC2131], and uses message number 10 300 in the DHCP Message Type option (option 53). The DHCPLEASEQUERY 301 message has the following pertinent message contents: 303 o There MUST be a Relay Agent Information option (option 82) with 304 only a Remote ID sub-option (sub-option 2) in the DHCPLEASEQUERY 305 message. 307 o Parameter Request List option MUST be populated by the access 308 concentrator with Associated-IP option. The giaddr and other 309 options listed in Parameter Request List option are set as 310 explained in section 6.2 of RFC 4388 [RFC4388]. 312 o The ciaddr field MUST be set to zero. 314 o The values of htype, hlen, and chaddr MUST be set to zero. 316 o The Client Identifier option (option 61) MUST NOT appear in the 317 packet. 319 The DHCPLEASEQUERY message SHOULD be sent to a DHCP server that is 320 known to possess authoritative information concerning the Remote ID. 321 The DHCPLEASEQUERY message MAY be sent to more than one DHCP server, 322 and in the absence of information concerning which DHCP server might 323 possess authoritative information concerning the Remote ID, it SHOULD 324 be sent to all DHCP servers configured for the associated relay agent 325 (if any are known). 327 4.2. Responding to the DHCPLEASEQUERY Message 329 There are two possible responses to a DHCPLEASEQUERY message: 331 o DHCPLEASEUNKNOWN 333 The DHCPLEASEUNKNOWN message indicates that the client associated 334 with the Remote ID suboption of the DHCPLEASEQUERY message is not 335 allocated any lease or it is not managed by the server. 337 o DHCPLEASEACTIVE 339 The DHCPLEASEACTIVE message indicates that the server not only knows 340 the client specified in the DHCPLEASEQUERY message, but also knows 341 that there is an active lease for that client. 343 4.3. Building a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message 345 A DHCPLEASEACTIVE message is built by populating information 346 pertaining to the client associated with the IP address specified in 347 the ciaddr field. 349 In the case where more than one IP address has been involved in a 350 DHCP message exchange with the client specified by the Remote ID, 351 then the list of all those IP addresses MUST be returned in the 352 Associated-IP option, whether or not that option was requested as 353 part of the Parameter Request List option. This is intended for 354 maintaining backwards compatibility with RFC 4388 [RFC4388]. 356 For all other options that are specified in Parameter Request List, 357 the processing is same as mentioned in section 6.4.2 of RFC 4388 358 [RFC4388]. 360 In a DHCPLEASEUNKNOWN response message, the DHCP server MUST echo the 361 Option 82 received in the DHCPLEASEQUERY message. No other option is 362 included in the message. 364 4.4. Determining the IP address to be used in response 366 The IP address placed in the ciaddr field of a DHCPLEASEACTIVE 367 message MUST be the IP address with the latest client-last- 368 transaction-time associated with the client described by the Remote 369 ID specified in the DHCPLEASEQUERY message. 371 If there is only a single IP address that fulfills this criteria, 372 then it MUST be placed in the ciaddr field of the DHCPLEASEACTIVE 373 message. 375 In the case where more than one IP address has been accessed by the 376 client specified by the Remote ID, then the DHCP server MUST return 377 the IP address returned to the client in the most recent transaction 378 with the client unless the DHCP server has been configured by the 379 server administrator to use some other preference mechanism. 381 4.5. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message 383 The server unicasts the DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message 384 to the address specified in the giaddr field of the DHCPLEASEQUERY 385 message. 387 4.6. Receiving a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message 389 When a DHCPLEASEACTIVE message is received in response to the 390 DHCPLEASEQUERY message, it means that there is currently an active 391 lease associated with the Remote ID in the DHCP server. The access 392 concentrator SHOULD use the information in the htype, hlen, and 393 chaddr fields of the DHCPLEASEACTIVE as well as Relay Agent 394 Information option included in the packet to refresh its location 395 information for this IP address. An access concentrator is likely to 396 query by IP address for all the IP addresses specified in the 397 Associated-IP option in the response, if any, at this point in time. 399 When a DHCPLEASEUNKNOWN message is received by an access concentrator 400 that had sent out a DHCPLEASEQUERY message, it means that the DHCP 401 server does not have definitive information concerning the DHCP 402 client specified in the Remote ID sub-option of the DHCPLEASEQUERY 403 message. The access concentrator MAY store this information for 404 future use. However, another DHCPLEASEQUERY message to the same DHCP 405 server SHOULD NOT be attempted with the same Remote ID sub-option. 407 For lease query by Remote ID, the impact of negative caching is 408 greatly reduced as the response leads to "definitive" information on 409 all the nodes connected behind the connection. Note that in case of 410 the data-driven approach [RFC4388], a node spoofing several IP 411 addresses can lead to negative caching of greater magnitude. Another 412 important change that this draft brings is the removal of periodic 413 lease queries generated from negative caching caused by 414 DHCPLEASEUNKNOWN. Since the information obtained through query by 415 Remote ID is complete, there is no need of attempting lease query 416 again for the same connection. 418 4.7. Receiving No Response to the DHCPLEASEQUERY Message 420 The condition of access concentrator receiving no response to a 421 DHCPLEASEQUERY message should be handled in the same manner as 422 suggested in RFC 4388 [RFC4388]. 424 4.8. Lease Binding Data Storage Requirements 426 Implementation Note: 428 To generate replies for a lease query by Remote ID effeciently, a 429 DHCP server should index the lease binding data structures using 430 Remote ID. 432 4.9. Using the DHCPLEASEQUERY Message with Multiple DHCP Servers 434 This scenario should be handled in the same way it is done in RFC 435 4388 [RFC4388]. 437 5. RFC 4388 Considerations 439 This document is compatible with RFC 4388 [RFC4388] based 440 implementations, which means that a client that supports this 441 extension can work with a server not supporting this document, 442 provided it uses RFC 4388 [RFC4388] defined query types. Also, a 443 server supporting this document can work with a client not supporting 444 this query type. However, there are some changes that this document 445 proposes with respect to RFC 4388 [RFC4388]. Implementers extending 446 RFC 4388 [RFC4388] implementations to support this document should 447 take note of the following points: 449 o There may be cases where a query by IP address/MAC address/Client 450 Identifier has an option 82 containing Remote ID. In that case, 451 the query will still be recognized as query by IP address/MAC 452 address/Client Identifier as specified by RFC 4388 [RFC4388]. 454 o Section 6.4 of RFC 4388 [RFC4388] suggests that a DHCPLEASEUNKNOWN 455 MUST NOT have any other option present. But for a query by Remote 456 ID, option 82 MUST be present in the reply. 458 6. Security Considerations 460 This document does not introduce any new security concerns beyond 461 those specified in the original lease query protocol RFC 4388 462 [RFC4388] specifications. 464 7. IANA Considerations 466 This document does not introduce any new namespaces for the IANA to 467 manage. 469 8. Acknowledgments 471 Copious amounts of text in this document are derived from RFC 4388 472 [RFC4388]. Kim Kinnear, Damien Neil, Stephen Jacob, Ted Lemon and 473 Alfred Hoenes provided valuable feedback on this document. 475 9. References 477 9.1. Normative Reference 479 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 480 Requirement Levels", BCP 14, RFC 2119, March 1997. 482 [RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration 483 Protocol (DHCP) Leasequery", RFC 4388, February 2006. 485 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 486 RFC 2131, March 1997. 488 [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", 489 RFC 3046, January 2001. 491 9.2. Informative Reference 493 [RFC951] Croft, B. and J. Gilmore, "Bootstrap Protocol (BOOTP)", 494 RFC 951, September 1985. 496 [RFC1542] Wimer, W., "Clarifications and Extensions for the 497 Bootstrap Protocol", RFC 1542, October 1993. 499 Authors' Addresses 501 Pavan Kurapati 502 Juniper Networks Ltd. 503 Embassy Prime Buildings, C.V.Raman Nagar 504 Bangalore 560 093 505 India 507 Email: kurapati@juniper.net 508 URI: http://www.juniper.net/ 510 D.T.V Ramakrishna Rao 511 Infosys Technologies Ltd. 512 44 Electronics City, Hosur Road 513 Bangalore 560 100 514 India 516 Email: ramakrishnadtv@infosys.com 517 URI: http://www.infosys.com/ 519 Bharat Joshi 520 Infosys Technologies Ltd. 521 44 Electronics City, Hosur Road 522 Bangalore 560 100 523 India 525 Email: bharat_joshi@infosys.com 526 URI: http://www.infosys.com/