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'DISC') (Obsoleted by RFC 2461) == Outdated reference: A later version (-03) exists of draft-ietf-ipngwg-trans-ethernet-01 -- Possible downref: Non-RFC (?)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: 12 errors (**), 0 flaws (~~), 6 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 18, 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 each node. If a Router Advertisement received on 60 an FDDI interface has an MTU option specifying an MTU larger than 61 4352, or larger than a manually configured value, that MTU option 62 may be logged to system management but must be otherwise ignored. 64 For purposes of this document, information received from DHCP is 65 considered "manually configured" and the term FDDI includes CDDI. 67 3. Frame Format 69 FDDI provides both synchronous and asynchronous transmission, with 70 the latter class further subdivided by the use of restricted and 71 unrestricted tokens. Only asynchronous transmission with 72 unrestricted tokens is required for FDDI interoperability. 73 Accordingly, IPv6 packets shall be sent in asynchronous frames using 74 unrestricted tokens. The robustness principle dictates that nodes 75 should be able to receive synchronous frames and asynchronous frames 76 sent using restricted tokens. 78 IPv6 packets are transmitted in LLC/SNAP frames, using long-format 79 (48 bit) addresses. The data field contains the IPv6 header and 80 payload and is followed by the FDDI Frame Check Sequence, Ending 81 Delimiter, and Frame Status symbols. 83 0 1 84 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 85 +-+-+-+-+-+-+-+-+ 86 | FC | 87 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 88 | Destination | 89 +- -+ 90 | FDDI | 91 +- -+ 92 | Address | 93 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 94 | Source | 95 +- -+ 96 | FDDI | 97 +- -+ 98 | Address | 99 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 100 | DSAP | SSAP | 101 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 102 | CTL | OUI ... | 103 +-+-+-+-+-+-+-+-+ + 104 | ... OUI | 105 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 106 | Ethertype | 107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 108 | IPv6 | 109 +- -+ 110 | header | 111 +- -+ 112 | and | 113 +- -+ 114 / payload ... / 115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 117 (Each tic mark represents one bit.) 119 FDDI Header Fields: 121 FC The Frame Code must be in the range 50 to 57 122 hexadecimal, inclusive, with the three low order bits 123 indicating the frame priority. The Frame Code should be 124 in the range 51 to 57 hexadecimal, inclusive, for 125 reasons given in the next section. 127 DSAP, SSAP Both the DSAP and SSAP fields shall contain the value AA 128 hexadecimal, indicating SNAP encapsulation. 130 CTL The Control field shall be set to 03 hexadecimal, 131 indicating Unnumbered Information. 133 OUI The Organizationally Unique Identifier shall be set to 134 000000 hexadecimal. 136 Ethertype The ethernet protocol type ("ethertype") shall be set to 137 the value 86DD hexadecimal. 139 4. Interaction with Bridges 141 802.1d MAC bridges which connect different media, for example 142 Ethernet and FDDI, have become very widespread. Some of them do 143 IPv4 packet fragmentation and/or support IPv4 Path MTU discovery 144 [PMTU], many others do not, or do so incorrectly. Use of IPv6 in a 145 bridged mixed-media environment should not depend on support from 146 MAC bridges. 148 For correct operation when mixed media are bridged together, the 149 smallest MTU of all the media must be advertised by routers in an 150 MTU option. If there are no routers present, this MTU must be 151 manually configured in each node which is connected to a medium with 152 larger default MTU. Multicast packets on such a bridged network 153 must not be larger than the smallest MTU of any of the bridged 154 media. Often, the subnetwork topology will support larger unicast 155 packets to be exchanged between certain pairs of nodes. To take 156 advantage of high-MTU paths when possible, nodes transmitting IPv6 157 on FDDI should implement the following simple mechanism for "FDDI 158 adjacency detection". 160 A node which implements FDDI adjacency detection and has it enabled 161 on an FDDI interface must set a non-zero LLC priority in all 162 Neighbor Advertisement, Neighbor Solicitation and, if applicable, 163 Router Advertisement frames transmitted on that interface. (In IEEE 164 802 language, the user_priority parameter of the M_UNITDATA.request 165 primitive must not be zero.) If FDDI adjacency detection has been 166 disabled on an FDDI interface, the priority field of those frames 167 must be zero. 169 Note that an IPv6 frame which originated on an Ethernet, or 170 traversed an Ethernet, before being translated by an 802.1d bridge 171 and delivered to a node's FDDI interface will have zero in the 172 priority field, as required by [BRIDGE]. (There's a fine point 173 here: a conforming bridge may provide a management-settable Outbound 174 User Priority parameter for each port. However, the author is 175 unaware of any product that provides this optional capability and, 176 in any case, when the parameter is available its default value is 177 zero.) 179 If a node N1 receives, in an FDDI frame with a non-zero LLC 180 priority, a valid Router Advertisement, Neighbor Advertisement, or 181 Neighbor Solicitation from a node N2, then N1 may send unicast IPv6 182 packets to N2 with sizes up to the default IPv6 FDDI MTU (4352 183 octets), regardless of any smaller MTU configured manually or 184 received in a Router Advertisement MTU option. N2 may be the IPv6 185 destination or the next hop router to the destination. 187 Nodes implementing FDDI adjacency detection must provide a 188 configuration option to disable the mechanism. This option may be 189 used when a smaller MTU is desired for reasons other than mixed- 190 media bridging. By default, FDDI adjacency detection should be 191 enabled. 193 The only contemplated use of the LLC priority field of the FC octet 194 is to aid in per-destination MTU determination. It would be 195 sufficient for that purpose to require only that Router 196 Advertisements, Neighbor Advertisements, and Neighbor Solicitations 197 sent on FDDI always have non-zero priority. However, it may be 198 simpler or more useful to transmit all IPv6 packets on FDDI with 199 non-zero priority. 201 5. Stateless Autoconfiguration 203 The Interface Identifier [AARCH] for an FDDI interface is based on 204 the EUI-64 identifier [EUI64] derived from the interface's built-in 205 48-bit IEEE 802 address. The EUI-64 is formed as follows. 206 (Canonical bit order is assumed throughout.) 208 The OUI of the FDDI MAC address (the first three octets) becomes the 209 company_id of the EUI-64 (the first three octets). The fourth and 210 fifth octets of the EUI are set to the fixed value FFFE hexadecimal. 211 The last three octets of the FDDI MAC address become the last three 212 octets of the EUI-64. 214 The Interface Identifier is then formed from the EUI-64 by 215 complementing the "Universal/Local" (U/L) bit, which is the next- 216 to-lowest order bit of the first octet of the EUI-64. For futher 217 discussion on this point, see [ETHER] and [AARCH]. 219 For example, the Interface Identifier for an FDDI interface whose 220 built-in address is, in hexadecimal, 222 34-56-78-9A-BC-DE 224 would be 226 36-56-78-FF-FE-9A-BC-DE. 228 A different MAC address set manually or by software should not be 229 used to derive the Interface Identifier. If such a MAC address must 230 be used, its global uniqueness property should be reflected in the 231 value of the U/L bit. 233 An IPv6 address prefix used for stateless autoconfiguration [AARCH] 234 of an FDDI interface must have a length of 64 bits. 236 6. Link-Local Addresses 238 The IPv6 link-local address [AARCH] for an FDDI interface is formed 239 by appending the Interface Identifier, as defined above, to the 240 prefix FE80::/64. 242 10 bits 54 bits 64 bits 243 +----------+-----------------------+----------------------------+ 244 |1111111010| (zeros) | Interface Identifier | 245 +----------+-----------------------+----------------------------+ 247 7. Address Mapping -- Unicast 249 The procedure for mapping IPv6 unicast addresses into FDDI link- 250 layer addresses is described in [DISC]. The Source/Target Link- 251 layer Address option has the following form when the link layer is 252 FDDI. 254 0 1 255 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 257 | Type | Length | 258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 259 | | 260 +- FDDI -+ 261 | | 262 +- Address -+ 263 | | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 Option fields: 268 Type 1 for Source Link-layer address. 269 2 for Target Link-layer address. 271 Length 1 (in units of 8 octets). 273 FDDI Address 274 The 48 bit FDDI IEEE 802 address, in canonical bit 275 order. This is the address the interface currently 276 responds to, and may be different from the built-in 277 address used to derive the Interface Identifier. 279 8. Address Mapping -- Multicast 281 An IPv6 packet with a multicast destination address DST, consisting 282 of the sixteen octets DST[1] through DST[16], is transmitted to the 283 FDDI multicast address whose first two octets are the value 3333 284 hexadecimal and whose last four octets are the last four octets of 285 DST. 287 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 288 |0 0 1 1 0 0 1 1|0 0 1 1 0 0 1 1| 289 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 290 | DST[13] | DST[14] | 291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 | DST[15] | DST[16] | 293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 295 9. Security Considerations 297 The method of derivation of Interface Identifiers from MAC addresses 298 is intended to preserve global uniqueness when possible. However, 299 there is no protection from duplication through accident or forgery. 301 10. Acknowledgments 303 Erik Nordmark and Matt Thomas contributed to the method for 304 interaction with bridges. 306 11. References 308 [AARCH] R. Hinden, S. Deering "IP Version 6 Addressing 309 Architecture", Currently draft-ietf-ipngwg-addr-arch-v2- 310 02.txt. 312 [ACONF] S. Thomson, T. Narten, "IPv6 Stateless Address 313 Autoconfiguration", RFC 1971. 315 [BRIDGE]ISO/IEC 10038 : 1993 [ANSI/IEEE Std 802.1D, 1993 Edition] 316 "Media access control (MAC) bridges." 318 [DISC] T. Narten, E. Nordmark, W. A. Simpson, "Neighbor Discovery 319 for IP Version 6 (IPv6)", RFC 1970. 321 [ETHER] M. Crawford, "Transmission of IPv6 Packets over Ethernet 322 Networks", currently draft-ietf-ipngwg-trans-ethernet- 323 01.txt. 325 [EUI64] "64-Bit Global Identifier Format Tutorial", 326 http://standards.ieee.org/db/oui/tutorials/EUI64.html. 328 [IPV6] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) 329 Specification", RFC 1883. 331 [KWORD] S. Bradner, "Key words for use in RFCs to Indicate 332 Requirement Levels," RFC 2119. 334 [PMTU] J. Mogul, S. Deering "Path MTU Discovery", RFC 1191. 336 12. Author's Address 338 Matt Crawford 339 Fermilab MS 368 340 PO Box 500 341 Batavia, IL 60510 342 USA 344 Phone: +1 630 840-3461 346 EMail: crawdad@fnal.gov