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All references will be assumed normative when checking for downward references. Miscellaneous warnings: ---------------------------------------------------------------------------- == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: In the IPv6 context, IPComp is viewed as an end-to-end payload, and MUST not apply to hop-by-hop, routing, and fragmentation extension headers. The compression is applied starting at the first IP Header Option field that does not carry information that must be examined and processed by nodes along a packet's delivery path, if such an IP Header Option field exists, and continues to the ULP payload of the IP datagram. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 2000) is 8713 days in the past. Is this intentional? 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 1700 (Obsoleted by RFC 3232) ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 2409 (ref. 'IKE') (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 2407 (ref. 'SECDOI') (Obsoleted by RFC 4306) -- Possible downref: Non-RFC (?) normative reference: ref. 'V42BIS' Summary: 8 errors (**), 0 flaws (~~), 4 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT A. Shacham, Cisco 2 Network Working Group B. Monsour, Consultant 3 R. Pereira, Cisco 4 M. Thomas, Consultant 5 June 2000 7 IP Payload Compression Protocol (IPComp) 8 10 Status of this Memo 12 This document is an Internet Draft and is in full conformance with 13 all provisions of Section 10 of RFC2026. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as 18 Internet-Drafts. 20 Internet Drafts are draft documents valid for a maximum of six months 21 and may be updated, replaced, or obsoleted by other documents at any 22 time. It is inapproporiate to use Internet Drafts as reference 23 material or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt. 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 To learn the current status of any Internet Draft, please check the 32 "1id-abstracts.txt" listing contained in the Internet Drafts Shadow 33 Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), 34 munnari.oz.au (Australia), ds.internic.net (US East Coast), or 35 ftp.isi.edu (US West Coast). 37 Abstract 39 This document describes a protocol intended to provide lossless 40 compression for Internet Protocol datagrams in an Internet 41 environment. 43 1. Introduction 45 IP payload compression is a protocol to reduce the size of IP 46 datagrams. This protocol will increase the overall communication 47 performance between a pair of communicating hosts/gateways ("nodes") 48 by compressing the datagrams, provided the nodes have sufficient 49 computation power, through either CPU capacity or a compression 50 coprocessor, and the communication is over slow or congested links. 52 IP payload compression is especially useful when encryption is 53 applied to IP datagrams. Encrypting the IP datagram causes the data 54 to be random in nature, rendering compression at lower protocol 55 layers (e.g., PPP Compression Control Protocol [RFC-1962]) 56 ineffective. If both compression and encryption are required, 57 compression MUST be applied before encryption. 59 This document defines the IP payload compression protocol (IPComp), 60 the IPComp packet structure, the IPComp Association (IPCA), and 61 several methods to negotiate the IPCA. 63 Other documents shall specify how a specific compression algorithm 64 can be used with the IP payload compression protocol. Such 65 algorithms are beyond the scope of this document. 67 1.1. Specification of Requirements 69 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 70 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 71 document are to be interpreted as described in RFC 2119 [RFC-2119]. 73 2. Compression Process 75 The compression processing of IP datagrams has two phases: 76 compressing of outbound IP datagrams ("compression") and 77 decompressing of inbound datagrams ("decompression"). The 78 compression processing MUST be lossless, ensuring that the IP 79 datagram, after being compressed and decompressed, is identical to 80 the original IP datagram. 82 Each IP datagram is compressed and decompressed by itself without any 83 relation to other datagrams ("stateless compression"), as IP 84 datagrams may arrive out of order or not arrive at all. Each 85 compressed IP datagram encapsulates a single IP payload. 87 Processing of inbound IP datagrams MUST support both compressed and 88 non-compressed IP datagrams, in order to meet the non-expansion 89 policy requirements, as defined in section 2.2. 91 The compression of outbound IP datagrams MUST be done before any IP 92 security processing, such as encryption and authentication, and 93 before any fragmentation of the IP datagram. In addition, in IP 94 version 6 [RFC-2460], the compression of outbound IP datagrams MUST 95 be done before the addition of either a Hop-by-Hop Options header or 96 a Routing Header, since both carry information that must be examined 97 and processed by possibly every node along a packet's delivery path, 98 and therefore MUST be sent in the original form. 100 Similarly, the decompression of inbound IP datagrams MUST be done 101 after the reassembly of the IP datagrams, and after the completion of 102 all IP security processing, such as authentication and decryption. 104 2.1. Compressed Payload 106 The compression is applied to a single array of octets, which are 107 contiguous in the IP datagram. This array of octets always ends at 108 the last octet of the IP packet payload. Note: A contiguous array of 109 octets in the IP datagram may be not contiguous in physical memory. 111 In IP version 4 [RFC-0791], the compression is applied to the payload 112 of the IP datagram, starting at the first octet following the IP 113 header, and continuing through the last octet of the datagram. No 114 portion of the IP header or the IP header options is compressed. 115 Note: In the case of an encapsulated IP header (e.g., tunnel mode 116 encapsulation in IPsec), the datagram payload is defined to start 117 immediately after the outer IP header; accordingly, the inner IP 118 header is considered part of the payload and is compressed. 120 In the IPv6 context, IPComp is viewed as an end-to-end payload, and 121 MUST not apply to hop-by-hop, routing, and fragmentation extension 122 headers. The compression is applied starting at the first IP Header 123 Option field that does not carry information that must be examined 124 and processed by nodes along a packet's delivery path, if such an IP 125 Header Option field exists, and continues to the ULP payload of the 126 IP datagram. 128 The size of a compressed payload, generated by the compression 129 algorithm, MUST be in whole octet units. 131 As defined in section 3, an IPComp header is inserted immediately 132 preceding the compressed payload. The original IP header is modified 133 to indicate the usage of the IPComp protocol and the reduced size of 134 the IP datagram. The original content of the Next Header (IPv6) or 135 protocol (IPv4) field is stored in the IPComp header. 137 The decompression is applied to a single contiguous array of octets 138 in the IP datagram. The start of the array of octets immediately 139 follows the IPComp header and ends at the last octet of the IP 140 payload. If the decompression process is successfully completed, the 141 IP header is modified to indicate the size of the decompressed IP 142 datagram, and the original next header as stored in the IPComp 143 header. The IPComp header is removed from the IP datagram and the 144 decompressed payload immediately follows the IP header. 146 2.2. Non-Expansion Policy 148 If the total size of a compressed payload and the IPComp header, as 149 defined in section 3, is not smaller than the size of the original 150 payload, the IP datagram MUST be sent in the original non-compressed 151 form. To clarify: If an IP datagram is sent non-compressed, no 152 IPComp header is added to the datagram. This policy ensures saving 153 the decompression processing cycles and avoiding incurring IP 154 datagram fragmentation when the expanded datagram is larger than MTU. 156 Small IP datagrams are likely to expand as a result of compression. 157 Therefore, a numeric threshold should be applied before compression, 158 where IP datagrams of size smaller than the threshold are sent in the 159 original form without attempting compression. The numeric threshold 160 is implementation dependent. 162 An IP datagram with payload that has been previously compressed tends 163 not to compress any further. The previously compressed payload may 164 be the result of external processes, such as compression applied by 165 an upper layer in the communication stack, or by an off-line 166 compression utility. An adaptive algorithm should be implemented to 167 avoid the performance hit. For example, if the compression of i 168 consecutive IP datagrams of an IPCA fails, the next k IP datagrams 169 are sent without attempting compression. If the next j datagrams are 170 also failing to compress, the next k+n datagrams are sent without 171 attempting compression. Once a datagram is compressed successfully, 172 the normal process of IPComp restarts. Such an adaptive algorithm, 173 including all the related thresholds, is implementation dependent. 175 During the processing of the payload, the compression algorithm MAY 176 periodically apply a test to determine the compressibility of the 177 processed data, similar to the requirements of [V42BIS]. The nature 178 of the test is algorithm dependent. Once the compression algorithm 179 detects that the data is non-compressible, the algorithm SHOULD stop 180 processing the data, and the payload is sent in the original non- 181 compressed form. 183 3. Compressed IP Datagram Header Structure 185 A compressed IP datagram is encapsulated by modifying the IP header 186 and inserting an IPComp header immediately preceding the compressed 187 payload. This section defines the IP header modifications both in 188 IPv4 and IPv6, and the structure of the IPComp header. 190 3.1. IPv4 Header Modifications 192 The following IPv4 header fields are set before transmitting the 193 compressed IP datagram: 195 Total Length 197 The length of the entire encapsulated IP datagram, including 198 the IP header, the IPComp header and the compressed payload. 200 Protocol 202 The Protocol field is set to 108, IPComp Datagram, [RFC-1700]. 204 Header Checksum 206 The Internet Header checksum [RFC-0791] of the IP header. 208 All other IPv4 header fields are kept unchanged, including any header 209 options. 211 3.2. IPv6 Header Modifications 213 The following IPv6 header fields are set before transmitting the 214 compressed IP datagram: 216 Payload Length 218 The length of the compressed IP payload. 220 Next Header 222 The Next Header field is set to 108, IPComp Datagram, [RFC- 223 1700]. 225 All other IPv6 header fields are kept unchanged, including any non- 226 compressed header options. 228 The IPComp header is placed in an IPv6 packet using the same rules as 229 the IPv6 Fragment Header. However if an IPv6 packet contains both an 230 IPv6 Fragment Header and an IPComp header, the IPv6 Fragment Header 231 MUST precede the IPComp header in the packet. Note: Other IPv6 232 headers may be present between the IPv6 Fragment Header and the 233 IPComp header. 235 3.3. IPComp Header Structure 237 The four-octet header has the following structure: 239 0 1 2 3 240 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 1 241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 242 | Next Header | Flags | Compression Parameter Index | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 245 Next Header 247 8-bit selector. Stores the IPv4 Protocol field or the IPv6 Next 248 Header field of the original IP header. 250 Flags 252 8-bit field. Reserved for future use. MUST be set to zero. 253 MUST be ignored by the receiving node. 255 Compression Parameter Index (CPI) 257 16-bit index. The CPI is stored in network order. The values 258 0-63 define well-known compression algorithms, which require no 259 additional information, and are used for manual setup. The 260 values themselves are identical to IPCOMP Transform identifiers 261 as defined in [SECDOI]. Consult [SECDOI] for an initial set of 262 defined values and for instructions on how to assign new values. 264 The values 64-255 are reserved for future use. The values 265 256-61439 are negotiated between the two nodes in definition of 266 an IPComp Association, as defined in section 4. Note: When 267 negotiating one of the well-known algorithms, the nodes MAY 268 select a CPI in the pre-defined range 0-63. The values 269 61440-65535 are for private use among mutually consenting 270 parties. Both nodes participating can select a CPI value 271 independently of each other and there is no relationship 272 between the two separately chosen CPIs. The outbound IPComp 273 header MUST use the CPI value chosen by the decompressing node. 274 The CPI in combination with the destination IP address uniquely 275 identifies the compression algorithm characteristics for the 276 datagram. 278 4. IPComp Association (IPCA) Negotiation 280 To utilize the IPComp protocol, two nodes MUST first establish an 281 IPComp Association (IPCA) between them. The IPCA includes all 282 required information for the operation of IPComp, including the 283 Compression Parameter Index (CPI), the mode of operation, the 284 compression algorithm to be used, and any required parameter for the 285 selected compression algorithm. The IPComp mode of operation is 286 either a node-to-node policy where IPComp is applied to every IP 287 packet between the nodes, or an ULP session based policy where only 288 selected ULP sessions between the nodes are using IPComp. For each 289 IPCA, a different compression algorithm may be negotiated in each 290 direction, or only one direction may be compressed. The default is 291 "no IPComp compression". 293 The IPCA is established by dynamic negotiations or by manual 294 configuration. The dynamic negotiations SHOULD use the Internet 295 Key Exchange protocol [IKE], where IPsec is present. The dynamic 296 negotiations MAY be implemented through a different protocol. 298 4.1. Use of IKE 300 For IPComp in the context of IP Security, IKE provides the necessary 301 mechanisms and guidelines for establishing IPCA. Using IKE, IPComp 302 can be negotiated as stand-alone or in conjunction with other IPsec 303 protocols. 305 An IPComp Association is negotiated by the initiator using a Proposal 306 Payload, which includes one or more Transform Payloads. The Proposal 307 Payload specifies the IP Payload Compression Protocol in the protocol 308 ID field and each Transform Payload contains the specific compression 309 algorithm(s) being offered to the responder. 311 The CPI is sent in the SPI field of the proposal, with the SPI size 312 field set to match. The CPI SHOULD be sent as a 16-bit number, with 313 the SPI size field set to 2. Alternatively, the CPI MAY be sent as a 314 32-bit value, with the SPI size field set to 4. In this case, the 315 16-bit CPI number MUST be placed in the two least significant octets 316 of the SPI field, while the two most significant octets MUST be set 317 to zero, and MUST be ignored by the receiving node. The receiving 318 node MUST be able to process both forms of the CPI proposal. 320 In the Internet IP Security Domain of Interpretation (DOI), IPComp is 321 negotiated as the Protocol ID PROTO_IPCOMP. The compression 322 algorithm is negotiated as one of the defined IPCOMP Transform 323 Identifiers. 325 The following attributes are applicable to IPComp proposals: 327 Encapsulation Mode 329 To suggest a non-default Encapsulation Mode (such as Tunnel 330 Mode), an IPComp proposal MUST include an Encapsulation Mode 331 attribute. If the Encapsulation Mode is unspecified, the 332 default value of Transport Mode is assumed. 334 Lifetime 336 An IPComp proposal uses the Life Duration and Life Type 337 attributes to suggest life duration to the IPCA. 339 When IPComp is negotiated as part of a Protection Suite, all the 340 logically related offers must be consistent. However, an IPComp 341 proposal SHOULD NOT include attributes that are not applicable to 342 IPComp. An IPComp proposal MUST NOT be rejected because it does not 343 include attributes of other protocols in the Protection Suite that 344 are not relevant to IPComp. When an IPComp proposal includes such 345 attributes, those attributes MUST be ignored when setting the IPCA, 346 and therefore ignored in the operation of IPComp. 348 Implementation note: 350 A node can avoid the computation necessary for determining the 351 compression algorithm from the CPI if it is using one of the 352 well-known algorithms; this can save time in the decompression 353 process. A node can do this by negotiating a CPI equal in value 354 to the pre-defined Transform identifier of that compression 355 algorithm. Specifically: A node MAY offer a CPI in the 356 pre-defined range by sending a Proposal Payload that MUST contain 357 a single Transform Payload, which is identical to the CPI. When 358 proposing two or more Transform Payloads, a node MAY offer CPIs in 359 the pre-defined range by using multiple IPComp proposals -- each 360 MUST include a single Transform Payload. To clarify: If a 361 Proposal Payload contains two or more Transform Payloads, the CPI 362 MUST be in the negotiated range. A receiving node MUST be able to 363 process each of these proposal forms. 365 4.2. Use of Non-IKE Protocol 367 The dynamic negotiations MAY be implemented through a protocol other 368 than IKE. Such a protocol is beyond the scope of this document. 370 4.3. Manual Configuration 372 Nodes may establish IPComp Associations using manual configuration. 373 For this method, a limited number of Compression Parameters Indexes 374 (CPIs) is designated to represent a list of specific compression 375 methods. 377 5. Security Considerations 379 When IPComp is used in the context of IPsec, it is believed not to 380 have an effect on the underlying security functionality provided by 381 the IPsec protocol; i.e., the use of compression is not known to 382 degrade or alter the nature of the underlying security architecture 383 or the encryption technologies used to implement it. 385 When IPComp is used without IPsec, IP payload compression potentially 386 reduces the security of the Internet, similar to the effects of IP 387 encapsulation [RFC-2003]. For example, IPComp may make it difficult 388 for border routers to filter datagrams based on header fields. In 389 particular, the original value of the Protocol field in the IP header 390 is not located in its normal positions within the datagram, and any 391 transport layer header fields within the datagram, such as port 392 numbers, are neither located in their normal positions within the 393 datagram nor presented in their original values after compression. A 394 filtering border router can filter the datagram only if it shares the 395 IPComp Association used for the compression. To allow this sort of 396 compression in environments in which all packets need to be filtered 397 (or at least accounted for), a mechanism must be in place for the 398 receiving node to securely communicate the IPComp Association to the 399 border router. This might, more rarely, also apply to the IPComp 400 Association used for outgoing datagrams. 402 6. References 404 [RFC-0791] Postel, J., Editor, "Internet Protocol", STD 5, RFC 791, 405 September 1981. 407 [RFC-1700] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, 408 RFC 1700, October 1994. Or see: 409 http://www.iana.org/numbers.html 411 [RFC-2460] Deering, S., and R. Hinden, "Internet Protocol, Version 6 412 (IPv6) Specification", RFC 2460, December 1998. 414 [RFC-1962] Rand, D., "The PPP Compression Control Protocol (CCP)", 415 RFC 1962, June 1996. 417 [RFC-2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 418 October 1996. 420 [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate 421 Requirement Levels", BCP 14, RFC 2119, March 1997. 423 [IKE] Harkins, D., and D. Carrel, "The Internet Key Exchange 424 (IKE)", RFC 2409, November 1998. 426 [SECDOI] Piper, D., "The Internet IP Security Domain of 427 Interpretation for ISAKMP", RFC 2407, November 1998. 429 [V42BIS] CCITT, "Data Compression Procedures for Data Circuit 430 Terminating Equipment (DCE) Using Error Correction 431 Procedures", Recommendation V.42 bis, January 1990. 433 Authors' Addresses 435 Abraham Shacham 436 Cisco Systems, Inc. 437 170 West Tasman Drive 438 San Jose, California 95134 439 United States of America 441 EMail: shacham@shacham.net 443 Bob Monsour 444 15723 Oak Knoll Drive 445 Los Gatos, California 95030 446 United States of America 448 EMail: bobmonsour@home.com 450 Roy Pereira 451 Cisco Systems, Inc. 452 55 Metcalfe Street 453 Ottawa, Ontario K1P 6L5 454 Canada 456 EMail: royp@cisco.com 458 Matt Thomas 459 3am Software Foundry 460 8053 Park Villa Circle 461 Cupertino, California 95014 462 United States of America 464 EMail: matt@3am-software.com 466 Comments 468 Comments should be addressed to the ippcp@external.cisco.com mailing 469 list and/or the author(s).