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Checking references for intended status: Experimental ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group I. Learmonth 3 Internet-Draft HamBSD 4 Obsoletes: 1226 (if approved) May 21, 2020 5 Intended status: Experimental 6 Expires: November 22, 2020 8 Internet Protocol Encapsulation of AX.25 Frames 9 draft-learmonth-intarea-rfc1226-bis-00 11 Abstract 13 This document describes a method for the encapsulation of AX.25 Link 14 Access Protocol for Amateur Packet Radio frames within IPv4 and IPv6 15 packets. Obsoletes RFC1226. 17 Note 19 Comments are solicited and should be addressed to the author(s). 21 The sources for this draft are at: 23 https://github.com/irl/draft-rfc1226-bis 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on November 22, 2020. 42 Copyright Notice 44 Copyright (c) 2020 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 1. Introduction 59 This document describes a method for the encapsulation of AX.25 Link 60 Access Protocol for Amateur Packet Radio [AX.25] frames within IPv4 61 and IPv6 packets. It obsoletes [RFC1226]. 63 AX.25 is a data link layer protocol originally derived from layer 2 64 of the X.25 protocol suite and designed for use by amateur radio 65 operators. It is used extensively by amateur packet radio networks 66 worldwide. 68 In addition to specifying how packets should be encapsulated, it 69 gives recommendations for DiffServ codepoint marking of the 70 encapsulating headers based on the AX.25 frame content and provides 71 security considerations for the use of this encapsulation method. 73 2. Terminology 75 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 76 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 77 document are to be interpreted as described in [RFC2119]. 79 3. Internet Protocol Encapsulation 81 Each AX.25 frame is encapsulated in one IPv4 or IPv6 datagram using 82 protocol number 93 as assigned in the Assigned Internet Protocol 83 Numbers registry [protocol-numbers]. For AX.25 version 2.0, the 84 maximum frame size expected is 330 bytes and implementations MUST be 85 prepared to handle frames of this size. Higher frame sizes can be 86 negotiated by AX.25 version 2.2 and so this is a minimum requirement 87 and not a limit. 89 HDLC framing elements (flags and zero-stuffing) are omitted, as the 90 IP datagram adequately delimits the beginning and end of each AX.25 91 frame. The CRC-16-CCITT frame check sequence (normally generated by 92 the HDLC transmission hardware) is included trailing the information 93 field. In all other respects, AX.25 frames are encapsulated 94 unaltered. 96 3.1. Priority Frames 98 In normal operation, the DiffServ codepoint field [RFC2474] in the 99 encapsulating IP header SHOULD be set to best effort (BE). The 100 exception to this is "priority frames" as specified for AX.25 version 101 2.2, including acknowledgement and digipeat frames, which SHOULD have 102 the DiffServ codepoint set to AF21 [RFC2597]. A slot is reserved on 103 the radio channel for the transmission of these frames and the use of 104 this codepoint will permit the frames to arrive promptly at the 105 station for transmission. 107 For the avoidance of doubt: on decapsulation the AX.25 frame MUST NOT 108 be modified based on the DiffServ codepoint on the received 109 encapsulating IP header. The receiver MUST NOT use the DiffServ 110 codepoint to infer anything about the nature of the encapsulated 111 packet. It has been shown that while the AF21 codepoint may be 112 remarked while crossing administrative boundaries, it is unlikely 113 that priority inversion will occur due to remarking where such 114 remarking occurs [Cust18]. 116 3.2. Automatic Packet Reporting System 118 Automatic Packet Reporting System [APRS] is an amateur radio-based 119 system for real time digital communications for local situational 120 awareness. APRS uses AX.25 frames for addressing, and additionally 121 assigns special meaning to some of the reserved bits of an AX.25 122 frame header. 124 As a special case, when used with the Automatic Packet Reporting 125 System [APRS], priority frames will not occur. If a tunnel is 126 configured as carrying APRS data, the DiffServ codepoint SHOULD by 127 default be set to AF11 [RFC2597]. Where the "Precedence Bit" 128 [RR-bits] is set (i.e. it is zero) in an APRS packet, the DiffServ 129 codepoint should be set to BE. Where the "Operator Present Bit" 130 [RR-bits] is set (i.e. it is zero), the DiffServ codepoint MAY be set 131 to AF21 [RFC2597]. 133 Again, for the avoidance of doubt: on decapsulation the AX.25 frame 134 MUST NOT be modified based on the DiffServ codepoint on the received 135 encapsulating IP header. The receiver MUST NOT use the DiffServ 136 codepoint to infer anything about the nature of the encapsulated 137 packet. It has been shown that while AF codepoints may be remarked 138 while crossing administrative boundaries, it is unlikely that 139 priority inversion will occur, either with the BE traffic or between 140 AF PHBs due to remarking where such remarking occurs [Cust18]. 142 It is possible depending on the nature of the tunnel that 143 decapsulated packets would need to be treated as third-party traffic 144 according to the APRS specification [APRS]. In this case, the Third- 145 Party Network Identifier "IPENC" SHOULD be used. This is to 146 differentiate traffic using IP encapsulation from APRS-IS traffic 147 [APRS-IS] and other third-party networks. 149 4. IANA Considerations 151 Protocol number 93 is assigned in [protocol-numbers] and should be 152 updated to point to this document. 154 5. Security Considerations 156 With the exception of control signals exchanged between earth command 157 stations and space stations in the amateur-satellite service, amateur 158 radio transmissions cannot be encoded for the purpose of obscuring 159 their meaning. In essence, this means that cryptography that 160 requires the use of secrets to decipher a message cannot be used 161 where the possibility exists that a packet will be transmitted by an 162 amateur radio station. 164 The CRC-16-CCITT provides for an integrity check but does not 165 guarantee the authenticity of the packet. In many jurisdictions it 166 is a requirement for amateur radio stations that are Internet 167 connected that they verify that packets for transmission have 168 originated from licensed radio amateurs. In order to provide this 169 guarantee, IPSec [RFC4301] SHOULD be employed to provide 170 authentication of packets. A transport mode SA SHOULD be negotiated 171 between the IP endpoints to use ESP [RFC4303] with NULL encryption 172 [RFC2410] with the traffic selector matching packets with IP protocol 173 number 93. In cases where traffic is guaranteed to not pass via an 174 amateur radio link, non-NULL encryption MAY be used. Non-NULL 175 encryption MUST NOT be used where there is the possibility that the 176 encapsulating packet will be transmitted via an amateur radio link. 178 When transmitted by an amateur radio station, many propagation modes 179 will permit wide reception of a packet. As such, receivers MUST 180 implement anti-replay protection by verifying received sequence 181 numbers [RFC4303]. The size of the anti-replay window may need to be 182 scaled to account not only for the speed of the link, but also for 183 packet loss that may occur on amateur radio links. Following 184 extended packet loss a sender may have advanced the sequence number 185 beyond the window size allowed. Dead peer detection [RFC7926] can be 186 used to renegotiate SAs in this case and so SHOULD be enabled for any 187 SA expected to traverse an amateur radio link that is expected to 188 have varying propagation charachteristics. 190 Given the need for anti-replay protection, it is not possible to 191 manually key the SAs. IKEv2 [RFC7926] SHOULD be used to establish 192 SAs. Beyond the above, the exact details of the automatic keying 193 protocol to use and its paramaters are not specified in this 194 document. 196 6. Acknowledgements 198 The author would like to acknowledge the work of Brian Kantor who 199 authored the original specification [RFC1226] that this document 200 updates. 202 7. References 204 7.1. Normative References 206 [AX.25] Tucson Amateur Packet Radio Corporation, "AX.25 Link 207 Access Protocol for Amateur Packet Radio Version 2.2", 208 July 1998, . 210 [protocol-numbers] 211 IANA, "Assigned Internet Protocol Numbers", 212 . 215 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 216 Requirement Levels", BCP 14, RFC 2119, 217 DOI 10.17487/RFC2119, March 1997, 218 . 220 [RFC2410] Glenn, R. and S. Kent, "The NULL Encryption Algorithm and 221 Its Use With IPsec", RFC 2410, DOI 10.17487/RFC2410, 222 November 1998, . 224 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 225 "Definition of the Differentiated Services Field (DS 226 Field) in the IPv4 and IPv6 Headers", RFC 2474, 227 DOI 10.17487/RFC2474, December 1998, 228 . 230 [RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski, 231 "Assured Forwarding PHB Group", RFC 2597, 232 DOI 10.17487/RFC2597, June 1999, 233 . 235 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 236 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 237 December 2005, . 239 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 240 RFC 4303, DOI 10.17487/RFC4303, December 2005, 241 . 243 [RR-bits] Bruninga, B., "APRS Future Use of AX.25 SSID RR Bits", 244 December 2012, . 246 7.2. Informative References 248 [APRS] Wade, I., Ed., "APRS Protocol Reference", August 2000, 249 . 251 [APRS-IS] Loveall, P., "APRS-IS", . 253 [Cust18] Custura, A., Secchi, R., and G. Fairhurst, "Exploring DSCP 254 modification pathologies in the Internet", Computer 255 Communications Vol. 127, pp. 86-94, 256 DOI 10.1016/j.comcom.2018.05.016, September 2018. 258 [RFC1226] Kantor, B., "Internet protocol encapsulation of AX.25 259 frames", RFC 1226, DOI 10.17487/RFC1226, May 1991, 260 . 262 [RFC7926] Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G., 263 Ceccarelli, D., and X. Zhang, "Problem Statement and 264 Architecture for Information Exchange between 265 Interconnected Traffic-Engineered Networks", BCP 206, 266 RFC 7926, DOI 10.17487/RFC7926, July 2016, 267 . 269 Author's Address 271 Iain R. Learmonth 272 HamBSD 274 Email: irl@hambsd.org