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'CONF') (Obsoleted by RFC 2462) ** Obsolete normative reference: RFC 1970 (ref. 'DISC') (Obsoleted by RFC 2461) == Outdated reference: A later version (-03) exists of draft-ietf-ipngwg-trans-ethernet-01 -- Possible downref: Non-RFC (?) normative reference: ref. 'EUI64' ** Obsolete normative reference: RFC 1883 (ref. 'IPV6') (Obsoleted by RFC 2460) Summary: 13 errors (**), 0 flaws (~~), 4 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 IPng Working Group Matt Crawford 2 Internet Draft Fermilab 3 July 3, 1997 5 Transmission of IPv6 Packets over FDDI Networks 6 8 Status of this Memo 10 This document is an Internet Draft. Internet Drafts are working 11 documents of the Internet Engineering Task Force (IETF), its Areas, 12 and its Working Groups. Note that other groups may also distribute 13 working documents as Internet Drafts. 15 Internet Drafts are draft documents valid for a maximum of six 16 months. Internet Drafts may be updated, replaced, or obsoleted by 17 other documents at any time. It is not appropriate to use Internet 18 Drafts as reference material or to cite them other than as a 19 "working draft" or "work in progress." 21 To learn the current status of any Internet-Draft, please check the 22 "1id-abstracts.txt" listing contained in the Internet Drafts Shadow 23 Directories on ds.internic.net (US East Coast), nic.nordu.net 24 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 25 Rim). 27 Distribution of this memo is unlimited. 29 1. Introduction 31 This memo specifies the MTU and frame format for transmission of 32 IPv6 packets on FDDI networks, including a method for MTU 33 determination in the presence of 802.1d bridges to other media. It 34 also specifies the method of forming IPv6 link-local addresses on 35 FDDI networks and the content of the Source/Target Link-layer 36 Address option used the Router Solicitation, Router Advertisement, 37 Neighbor Solicitation, Neighbor Advertisement and Redirect messages 38 when those messages are transmitted on an FDDI network. 40 This document replaces RFC 2019, "Transmission of IPv6 Packets Over 41 FDDI", which will become historic. 43 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 44 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 45 document are to be interpreted as described in [KWORD]. 47 2. Maximum Transmission Unit 49 FDDI permits a frame length of 4500 octets (9000 symbols), including 50 at least 22 octets (44 symbols) of Data Link encapsulation when 51 long-format addresses are used. Subtracting 8 octets of LLC/SNAP 52 header, this would, in principle, allow the IPv6 [IPV6] packet in 53 the Information field to be up to 4470 octets. However, it is 54 desirable to allow for the variable sizes and possible future 55 extensions of the MAC header and frame status fields. The default 56 MTU size for IPv6 packets on an FDDI network is therefore 4352 57 octets. This size may be reduced by a Router Advertisement [DISC] 58 containing an MTU option which specifies a smaller MTU, or by manual 59 configuration of a smaller value on each node. If a Router 60 Advertisement is received with an MTU option specifying an MTU 61 larger than the default or the manually configured value, that MTU 62 option may be logged to system management but must be otherwise 63 ignored. 65 For purposes of this document, information received from DHCP is 66 considered "manually configured". 68 3. Frame Format 70 FDDI provides both synchronous and asynchronous transmission, with 71 the latter class further subdivided by the use of restricted and 72 unrestricted tokens. Only asynchronous transmission with 73 unrestricted tokens is required for FDDI interoperability. 74 Accordingly, IPv6 packets shall be sent in asynchronous frames using 75 unrestricted tokens. The robustness principle dictates that nodes 76 should be able to receive synchronous frames and asynchronous frames 77 sent using restricted tokens. 79 IPv6 packets are transmitted in LLC/SNAP frames, using long-format 80 (48 bit) addresses. The data field contains the IPv6 header and 81 payload and is followed by the FDDI Frame Check Sequence, Ending 82 Delimiter, and Frame Status symbols. 84 0 1 85 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 86 +-+-+-+-+-+-+-+-+ 87 | FC | 88 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 89 | Destination | 90 +- -+ 91 | FDDI | 92 +- -+ 93 | Address | 94 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 95 | Source | 96 +- -+ 97 | FDDI | 98 +- -+ 99 | Address | 100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 101 | DSAP | SSAP | 102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 103 | CTL | OUI ... | 104 +-+-+-+-+-+-+-+-+ + 105 | ... OUI | 106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 107 | Ethertype | 108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 109 | IPv6 | 110 +- -+ 111 | header | 112 +- -+ 113 | and | 114 +- -+ 115 / payload ... / 116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 118 (Each tic mark represents one bit.) 120 FDDI Header Fields: 122 FC The Frame Code must be in the range 50 to 57 123 hexadecimal, inclusive, with the three low order bits 124 indicating the frame priority. The Frame Code should be 125 in the range 51 to 57 hexadecimal, inclusive, for 126 reasons given in the next section. 128 DSAP, SSAP Both the DSAP and SSAP fields shall contain the value AA 129 hexadecimal, indicating SNAP encapsulation. 131 CTL The Control field shall be set to 03 hexadecimal, 132 indicating Unnumbered Information. 134 OUI The Organizationally Unique Identifier shall be set to 135 000000 hexadecimal. 137 Ethertype The ethernet protocol type ("ethertype") shall be set to 138 the value 86DD hexadecimal. 140 4. Interaction with Bridges 142 802.1d MAC bridges which connect different media, for example 143 Ethernet and FDDI, have become very widespread. Some of them do 144 IPv4 packet fragmentation and/or support IPv4 Path MTU discovery 145 [PMTU], many others do not, or do so incorrectly. Use of IPv6 in a 146 bridged mixed-media environment should not depend on support from 147 MAC bridges. 149 For correct operation when mixed media are bridged together, the 150 smallest MTU of all the media must be advertised by routers in an 151 MTU option. If there are no routers present, this MTU must be 152 manually configured in each node which is connected to a medium with 153 larger default MTU. Multicast packets on such a bridged network 154 must not be larger than the smallest MTU of any of the bridged 155 media. Often, the subnetwork topology will support larger unicast 156 packets to be exchanged between certain pairs of nodes. To take 157 advantage of high-MTU paths when possible, nodes transmitting IPv6 158 on FDDI should implement the following simple mechanism for "FDDI 159 adjacency detection". 161 A node which implements FDDI adjacency detection and has it enabled 162 on an FDDI interface must set a non-zero LLC priority in all 163 Neighbor Advertisement, Neighbor Solicitation and, if applicable, 164 Router Advertisement frames transmitted on that interface. (In IEEE 165 802 language, the user_priority parameter of the M_UNITDATA.request 166 primitive must not be zero.) If FDDI adjacency detection has been 167 disabled on an FDDI interface, the priority field of those frames 168 must be zero. 170 Note that an IPv6 frame which originated on an Ethernet, or 171 traversed an Ethernet, before being translated by an 802.1d bridge 172 and delivered to a node's FDDI interface will have zero in the 173 priority field, as required by [BRIDGE]. (There's a fine point 174 here: a conforming bridge may provide a management-settable Outbound 175 User Priority parameter for each port. However, the author is 176 unaware of any product that provides this optional capability and, 177 in any case, the default value for the parameter is zero.) 178 If a node N1 receives, in an FDDI frame with a non-zero LLC 179 priority, a valid Router Advertisement, Neighbor Advertisement, or 180 Neighbor Solicitation from a node N2, then N1 may send unicast IPv6 181 packets to N2 with sizes up to the default IPv6 FDDI MTU (4352 182 octets), regardless of any smaller MTU configured manually or 183 received in a Router Advertisement MTU option. N2 may be the IPv6 184 destination or the next hop router to the destination. 186 Nodes implementing FDDI adjacency detection must provide a 187 configuration option to disable the mechanism. This option may be 188 used when a smaller MTU is desired for reasons other than mixed- 189 media bridging. By default, FDDI adjacency detection should be 190 enabled. 192 The only contemplated use of the LLC priority field of the FC octet 193 is to aid in per-destination MTU determination. It would be 194 sufficient for that purpose to require only that Router 195 Advertisements, Neighbor Advertisements, and Neighbor Solicitations 196 sent on FDDI always have non-zero priority. However, it may be 197 simpler or more useful to transmit all IPv6 packets on FDDI with 198 non-zero priority. 200 5. Stateless Autoconfiguration 202 The interface token [CONF] for an FDDI interface is based on the 203 EUI-64 identifier [EUI64] derived from the interface's built-in 48- 204 bit IEEE 802 address. The EUI-64 is formed as follows. (Canonical 205 bit order is assumed throughout.) 207 The OUI of the FDDI MAC address (the first three octets) becomes the 208 company_id of the EUI-64 (the first three octets). The fourth and 209 fifth octets of the EUI are set to the fixed value FFFE hexadecimal. 210 The last three octets of the FDDI MAC address become the last three 211 octets of the EUI-64. 213 The interface token is then formed from the EUI-64 by complementing 214 the "Universal/Local" (U/L) bit, which is the next-to-lowest order 215 bit of the first octet of the EUI-64. For futher discussion on this 216 point, see [ETHER]. 218 For example, the interface token for an FDDI interface whose built- 219 in address is, in hexadecimal, 221 34-56-78-9A-BC-DE 223 would be 224 36-56-78-FF-FE-9A-BC-DE. 226 A different MAC address set manually or by software should not be 227 used to derive the interface token. If such a MAC address must be 228 used, its global uniqueness property should be reflected in the 229 value of the U/L bit. 231 An IPv6 address prefix used for stateless autoconfiguration of an 232 FDDI interface must have a length of 64 bits. 234 6. Link-Local Addresses 236 The IPv6 link-local address [AARCH] for an FDDI interface is formed 237 by appending the interface token, as defined above, to the prefix 238 FE80::/64. 240 10 bits 54 bits 64 bits 241 +----------+-----------------------+----------------------------+ 242 |1111111010| (zeros) | Interface Token | 243 +----------+-----------------------+----------------------------+ 245 7. Address Mapping -- Unicast 247 The procedure for mapping IPv6 addresses into FDDI link-layer 248 addresses is described in [DISC]. The Source/Target Link-layer 249 Address option has the following form when the link layer is FDDI. 251 0 1 252 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 | Type | Length | 255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 256 | | 257 +- FDDI -+ 258 | | 259 +- Address -+ 260 | | 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 263 Option fields: 265 Type 1 for Source Link-layer address. 266 2 for Target Link-layer address. 268 Length 1 (in units of 8 octets). 270 FDDI Address 271 The 48 bit FDDI IEEE 802 address, in canonical bit 272 order. This is the address the interface currently 273 responds to, and may be different from the built-in 274 address used as the address token. 276 8. Address Mapping -- Multicast 278 An IPv6 packet with a multicast destination address DST, consisting 279 of the sixteen octets DST[1] through DST[16], is transmitted to the 280 FDDI multicast address whose first two octets are the value 3333 281 hexadecimal and whose last four octets are the last four octets of 282 DST. 284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 285 |0 0 1 1 0 0 1 1|0 0 1 1 0 0 1 1| 286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 287 | DST[13] | DST[14] | 288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 289 | DST[15] | DST[16] | 290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 9. Security Considerations 294 The method of derivation of interface tokens from MAC addresses is 295 intended to preserve global uniqueness when possible. However, 296 there is no protection from duplication through accident or forgery. 298 10. Acknowledgments 300 Erik Nordmark and Matt Thomas contributed to the method for 301 interaction with bridges. 303 11. References 305 [AARCH] R. Hinden, S. Deering "IP Version 6 Addressing 306 Architecture", RFC 1884. 308 [BRIDGE]ISO/IEC 10038 : 1993 [ANSI/IEEE Std 802.1D] Media access 309 control (MAC) bridges. 311 [CONF] S. Thomson, T. Narten, "IPv6 Stateless Address 312 Autoconfiguration", RFC 1971. 314 [DISC] T. Narten, E. Nordmark, W. A. Simpson, "Neighbor Discovery 315 for IP Version 6 (IPv6)", RFC 1970. 317 [ETHER] M. Crawford, "Transmission of IPv6 Packets over Ethernet 318 Networks", currently draft-ietf-ipngwg-trans-ethernet- 319 01.txt. 321 [EUI64] "64-Bit Global Identifier Format Tutorial", 322 http://standards.ieee.org/db/oui/tutorials/EUI64.html. 324 [IPV6] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) 325 Specification", RFC 1883. 327 [KWORD] S. Bradner, "Key words for use in RFCs to Indicate 328 Requirement Levels," RFC 2119. 330 [PMTU] J. Mogul, S. Deering "Path MTU Discovery", RFC 1191. 332 12. Author's Address 334 Matt Crawford 335 Fermilab MS 368 336 PO Box 500 337 Batavia, IL 60510 338 USA 340 Phone: +1 630 840-3461 342 EMail: crawdad@fnal.gov