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'13' Summary: 8 errors (**), 0 flaws (~~), 2 warnings (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Architecture Board M. St Johns, Ed. 3 Internet-Draft G. Huston, Ed. 4 Expires: February 12, 2004 IAB 5 August 14, 2003 7 Considerations on the use of a Service Identifier in Packet Headers 8 draft-iab-service-id-considerations-02.txt 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 other 17 groups may also distribute working documents as Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at http:// 25 www.ietf.org/ietf/1id-abstracts.txt. 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 This Internet-Draft will expire on February 12, 2004. 32 Copyright Notice 34 Copyright (C) The Internet Society (2003). All Rights Reserved. 36 Abstract 38 This memo describes some considerations relating to the use of IP 39 protocol number fields and payload protocol (e.g. TCP) port fields 40 to identify particular services that may be associated with that port 41 number or protocol number. 43 1. Introduction 45 This memo describes some considerations relating to the use of IP 46 protocol number fields and payload protocol (e.g. TCP) port or 47 service fields to identify particular services that may be associated 48 with that port number or protocol number. It is a general statement 49 regarding appropriate processing and use of service identifiers by 50 intermediate systems. 52 This memo points out that various measures by intermediate systems 53 that are intended to filter or prevent the transmission of traffic 54 based on the service identification within the traffic flow have 55 limited effect, with a major side-effect of forcing the affected 56 services to be redesigned using various forms of encapsulation or 57 dynamic port negotiation in order to remove the fixed service 58 identification from the IP packet headers. The IAB does not believe 59 this serves the general interests of the Internet community related 60 to the design of simple and reliable Internet applications. This memo 61 suggests some thought be given to control mechanisms that do not rely 62 on intermediary systems taking actions based on an assumed 63 relationship between the service identifier in the packet and the 64 actual service of which the packet is a part. 66 2. Service Identifiers 68 Although not necessarily by design, certain conventions have evolved 69 with respect to the IP protocol suite relative to the identification 70 of services within an IP traffic flow: 72 o Within the IP protocol suite, end point identifiers (e.g. TCP/ 73 UDP/SCTP port numbers, IP protocol numbers) are designed to 74 identify services to end points. In particular, TCP, UDP or SCTP 75 (Stream Control Transmission Protocol) port numbers are intended 76 to identify the source service location and the destination 77 service entity to the destination end point. 79 o The IP [2] datagram header contains the source and destination 80 address of the datagram as well as an indication of the upper- 81 level protocol (ULP) carried within the datagram. If the ULP is 82 either TCP [3], UDP [1], or SCTP [8] the payload will contain both 83 source and destination port numbers which allows differentiation 84 between services (e.g. TELNET, HTTP) and between multiple 85 instances of the same service between the pair of hosts described 86 by the source and destination address. 88 o By convention, for at least TCP and UDP, certain port numbers are 89 used as rendezvous points and are considered "well known" on the 90 source or destination side of the communication. Such rendezvous 91 points are maintained in an IANA registry currently located at 92 [11]. Specific registries for protocol and port numbers are at 93 [12] and [13]. 95 o Notwithstanding the "well-knownness" of any given port, port 96 numbers are only guaranteed to be meaningful to the end systems. 97 An intermediate system should generally not impute specific 98 meaning to any given port number, unless specifically indicated by 99 an end system (e.g. via the Resource Reservation Protocol 100 (RSVP)[4] ) or agreed to by convention among the end systems and 101 one or more specific intermediate systems (e.g. firewall 102 traversal for the IP Security Protocol (IPSEC)[5]). 104 o Some services make use of protocol interactions to dynamically 105 allocate service identifiers (i.e. port numbers) to specific 106 communications. One specific example of this is the Session 107 Initiation Protocol (SIP)[9]. The implication of this is that 108 intermediate systems cannot relate the service identifiers to the 109 actual service unless they participate in the protocols which 110 allocate the service identifiers, or are explicitly notified of 111 the outcome of the allocation. 113 o Various products and service-related mechanisms deployed today 114 take advantage of the fact that some service identifiers are 115 relatively stable (and well known) to do various things (e.g. 116 firewall filtering, QOS marking). 118 o Certain network operations, such as various forms of packet 119 encapsulation (e.g. tunnelling) and encryption, can occlude this 120 port number (or service identifier) while an IP packet is in 121 transit within the network. For example, both the IPSEC 122 Encapsulating Security Payload (ESP) [6] and Generic Routing 123 Encapsulation (GRE) [7] both provide means for tunneling an IP 124 datagram within another IP datagram. The service information 125 becomes obscured and, in some instances, encrypted. 127 o Cooperating end systems may elect to use arbitrarily selected port 128 numbers for any service. The port numbers used in such cases may 129 be statically defined, through coordinated configuration of the 130 cooperating end systems through use of a common application or 131 operating system, or by dynamic selection as an outcome of a 132 rendezvous protocol. 134 Intermediate system imposed service-based controls may block 135 legitimate uses by subscribers. For example, some service providers 136 are blocking port 25 (i.e. notionally SMTP) traffic for the stated 137 purpose of trying to prevent SPAM, but which can also block 138 legitimate email to the end user. 140 Attempts by intermediate systems to impose service-based controls on 141 communications against the perceived interests of the end parties to 142 the communication are often circumvented[10]. Services may be 143 tunneled within other services, proxied by a collaborating external 144 host (e.g. an anonymous redirector), or simply run over an alternate 145 port (e.g. port 8080 vs port 80 for HTTP). Another means of 146 circumvention is alteration of the service behaviour to use a dynamic 147 port negotiation phase, in order to avoid use of a constant port 148 address. 150 For the purposes of this memo a "party to a communication" is either 151 the sender, receiver or an authorized agent of the sender or receiver 152 in the path. 154 If intermediate systems take actions on behalf of one or more parties 155 to the communication or affecting the communication, a good rule of 156 thumb is they should only take actions that are beneficial to or 157 approved by one or more of the parties, within the operational 158 parameters of the service-specific protocol, or otherwise unlikely to 159 lead to widespread evasion by the user community. 161 3. Ramifications 163 The IAB observes that having stable and globally meaningful service 164 identifiers visible at points other than the end systems can be 165 useful for the purposes of determining network behavior and network 166 loading on a macro level. The IAB also observes that application 167 protocols that include dynamic port negotiation for both ends of a 168 connection tend to add to the complexity of the applications. 170 Dynamic port negotiation for a protocol may also limit or prohibit 171 its use in situations where the service provider (e.g. ISP or 172 employer) has instituted some form of service filtering through port 173 blocking mechanisms. 175 From this perspective of network and application utility, it is 176 preferable that no action or activity be undertaken by any agency, 177 carrier, service provider or organization which would tend to cause 178 end-users and protocol designers to generally obscure service 179 identification information from the IP packet header. 181 Nothing in this statement should be construed as opposing 182 encapsulation, application security, end-to-end encryption, or other 183 processes beneficial or specifically desired by the end-users. 185 4. Security Considerations 187 This document is a general statement regarding appropriate processing 188 and use of service identifiers by intermediate systems. If enough 189 agencies, carriers, service providers and organizations ignore the 190 concerns voiced here, the utility of port and protocol numbers, 191 general network analysis, end-user beneficial filtering (e.g. 192 preventing DDOS attacks), and other common uses of these service 193 identifiers might be adversely affected. 195 References 197 [1] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 198 1980. 200 [2] Postel, J., "Internet Protocol", STD 5, RFC 791, September 201 1981. 203 [3] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, 204 September 1981. 206 [4] Braden, B., Zhang, L., Berson, S., Herzog, S. and S. Jamin, 207 "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional 208 Specification", RFC 2205, September 1997. 210 [5] Kent, S. and R. Atkinson, "Security Architecture for the 211 Internet Protocol", RFC 2401, November 1998. 213 [6] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload 214 (ESP)", RFC 2406, November 1998. 216 [7] Farinacci, D., Li, T., Hanks, S., Meyer, D. and P. Traina, 217 "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000. 219 [8] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, 220 H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson, 221 "Stream Control Transmission Protocol", RFC 2960, October 2000. 223 [9] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 224 Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: 225 Session Initiation Protocol", RFC 3261, June 2002. 227 [10] New York Times, "STUDENTS EVADE UNIVERSITY TACTICS TO PROTECT 228 MEDIA FILES", 27th November 2002. 230 [11] IANA, "IANA Protocol Numbers and Assignment Services", May 231 2003, . 233 [12] IANA, "IANA Protocol Number Registry", May 2003, . 236 [13] IANA, "IANA Port Number Registry", May 2003, . 239 Authors' Addresses 241 Mike St Johns 242 Internet Architecture Board 244 Geoff Huston 245 Internet Architecture Board 247 Appendix A. IAB Members 249 Internet Architecture Board Members at the time this document was 250 completed were: 252 Bernard Aboba 253 Harald Alvestrand 254 Rob Austein 255 Leslie Daigle, Chair 256 Patrik Faltstrom 257 Sally Floyd 258 Jun-ichiro Itojun Hagino 259 Mark Handley 260 Geoff Huston 261 Charlie Kaufman 262 James Kempf 263 Eric Rescorla 264 Michael StJohns 266 Intellectual Property Statement 268 The IETF takes no position regarding the validity or scope of any 269 intellectual property or other rights that might be claimed to 270 pertain to the implementation or use of the technology described in 271 this document or the extent to which any license under such rights 272 might or might not be available; neither does it represent that it 273 has made any effort to identify any such rights. Information on the 274 IETF's procedures with respect to rights in standards-track and 275 standards-related documentation can be found in BCP-11. 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