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'IPV6') (Obsoleted by RFC 2460) Summary: 13 errors (**), 0 flaws (~~), 2 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPng Working Group Matt Crawford 3 Internet Draft Fermilab 4 March 21, 1997 6 Transmission of IPv6 Packets over FDDI Networks 7 9 Status of this Memo 11 This document is an Internet Draft. Internet Drafts are working 12 documents of the Internet Engineering Task Force (IETF), its Areas, 13 and its Working Groups. Note that other groups may also distribute 14 working documents as Internet Drafts. 16 Internet Drafts are draft documents valid for a maximum of six 17 months. Internet Drafts may be updated, replaced, or obsoleted by 18 other documents at any time. It is not appropriate to use Internet 19 Drafts as reference material or to cite them other than as a 20 "working draft" or "work in progress." 22 To learn the current status of any Internet-Draft, please check the 23 "1id-abstracts.txt" listing contained in the Internet Drafts Shadow 24 Directories on ds.internic.net (US East Coast), nic.nordu.net 25 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 26 Rim). 28 Distribution of this memo is unlimited. 30 1. Introduction 32 This memo specifies the MTU and frame format for transmission of 33 IPv6 packets on FDDI networks, including a method for MTU 34 determination in the presence of 802.1d bridges to other media. It 35 also specifies the method of forming IPv6 link-local addresses on 36 FDDI networks and the content of the Source/Target Link-layer 37 Address option used the Router Solicitation, Router Advertisement, 38 Neighbor Solicitation and Neighbor Advertisement messages when those 39 messages are transmitted on an FDDI network. 41 2. Maximum Transmission Unit 43 FDDI permits a frame length of 4500 octets (9000 symbols), including 44 at least 22 octets (44 symbols) of Data Link encapsulation when 45 long-format addresses are used. Subtracting 8 octets of LLC/SNAP 46 header, this would, in principle, allow the IPv6 [IPV6] packet in 47 the Information field to be up to 4470 octets. However, it is 48 desirable to allow for the variable sizes and possible future 49 extensions of the MAC header and frame status fields. The default 50 MTU size for IPv6 packets on an FDDI network is therefore 4352 51 octets. This size may be reduced by a Router Advertisement [DISC] 52 containing an MTU option which specifies a smaller MTU, or by manual 53 configuration of a smaller value on each node. If a Router 54 Advertisement is received with an MTU option specifying an MTU 55 larger than the default or the manually configured value, that MTU 56 option may be logged to system management but must be otherwise 57 ignored. 59 For purposes of this document, information received from DHCP is 60 considered "manually configured". 62 3. Frame Format 64 FDDI provides both synchronous and asynchronous transmission, with 65 the latter class further subdivided by the use of restricted and 66 unrestricted tokens. Only asynchronous transmission with 67 unrestricted tokens is required for FDDI interoperability. 68 Accordingly, IPv6 packets shall be sent in asynchronous frames using 69 unrestricted tokens. The robustness principle dictates that nodes 70 should be able to receive synchronous frames and asynchronous frames 71 sent using restricted tokens. 73 IPv6 packets are transmitted in LLC/SNAP frames, using long-format 74 (48 bit) addresses. The data field contains the IPv6 header and 75 payload and is followed by the FDDI Frame Check Sequence, Ending 76 Delimiter, and Frame Status symbols. 78 0 1 79 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 80 +-+-+-+-+-+-+-+-+ 81 | FC | 82 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 83 | Destination | 84 +- -+ 85 | FDDI | 86 +- -+ 87 | Address | 88 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 89 | Source | 90 +- -+ 91 | FDDI | 92 +- -+ 93 | Address | 94 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 95 | DSAP | SSAP | 96 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 97 | CTL | OUI ... | 98 +-+-+-+-+-+-+-+-+ + 99 | ... OUI | 100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 101 | Ethertype | 102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 103 | IPv6 | 104 +- -+ 105 | header | 106 +- -+ 107 | and | 108 +- -+ 109 / payload ... / 110 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 112 (Each tic mark represents one bit.) 114 FDDI Header Fields: 116 FC The Frame Code must be in the range 50 to 57 117 hexadecimal, inclusive, with the three low order bits 118 indicating the frame priority. The Frame Code should be 119 in the range 51 to 57 hexadecimal, inclusive, for 120 reasons given in the next section. 122 DSAP, SSAP Both the DSAP and SSAP fields shall contain the value AA 123 hexadecimal, indicating SNAP encapsulation. 125 CTL The Control field shall be set to 03 hexadecimal, 126 indicating Unnumbered Information. 128 OUI The Organizationally Unique Identifier shall be set to 129 000000 hexadecimal. 131 Ethertype The ethernet protocol type ("ethertype") shall be set to 132 the value 86DD hexadecimal. 134 4. Interaction with Bridges 136 802.1d MAC bridges which connect different media, for example 137 Ethernet and FDDI, have become very widespread. Some of them do 138 IPv4 packet fragmentation and/or support IPv4 Path MTU discovery 139 [PMTU], many others do not, or do so incorrectly. Use of IPv6 in a 140 bridged mixed-media environment should not depend on support from 141 MAC bridges. 143 For correct operation when mixed media are bridged together, the 144 smallest MTU of all the media must be advertised by routers in an 145 MTU option. If there are no routers present, this MTU must be 146 manually configured in each node which is connected to a medium with 147 larger default MTU. Multicast packets on such a bridged network 148 must not be larger than the smallest MTU of any of the bridged 149 media. Often, the subnetwork topology will support larger unicast 150 packets to be exchanged between certain pairs of nodes. To take 151 advantage of high-MTU paths when possible, nodes transmitting IPv6 152 on FDDI should implement the following simple mechanism for "FDDI 153 adjacency detection". 155 A node which implements FDDI adjacency detection and has it enabled 156 on an FDDI interface must set a non-zero LLC priority in all 157 Neighbor Advertisement, Neighbor Solicitation and, if applicable, 158 Router Advertisement frames transmitted on that interface. (In IEEE 159 802 language, the user_priority parameter of the M_UNITDATA.request 160 primitive must not be zero.) If FDDI adjacency detection has been 161 disabled on an FDDI interface, the priority field of those frames 162 must be zero. 164 Note that an IPv6 frame which originated on an Ethernet, or 165 traversed an Ethernet, before being translated by an 802.1d bridge 166 and delivered to a node's FDDI interface will have zero in the 167 priority field, as required by [BRIDGE]. (There's a fine point 168 here: a conforming bridge may provide a management-settable Outbound 169 User Priority parameter for each port. However, the author is 170 unaware of any product that provides this optional capability and, 171 in any case, the default value for the parameter is zero.) 172 If a node N1 receives, in an FDDI frame with a non-zero LLC 173 priority, a valid Router Advertisement, Neighbor Advertisement, or 174 Neighbor Solicitation from a node N2, then N1 may send unicast IPv6 175 packets to N2 with sizes up to the default IPv6 FDDI MTU (4352 176 octets), regardless of any smaller MTU configured manually or 177 received in a Router Advertisement MTU option. N2 may be the IPv6 178 destination or the next hop router to the destination. 180 Nodes implementing FDDI adjacency detection must provide a 181 configuration option to disable the mechanism. This option may be 182 used when a smaller MTU is desired for reasons other than mixed- 183 media bridging. By default, FDDI adjacency detection should be 184 enabled. 186 The only contemplated use of the LLC priority field of the FC octet 187 is to aid in per-destination MTU determination. It would be 188 sufficient for that purpose to require only that Router 189 Advertisements, Neighbor Advertisements, and Neighbor Solicitations 190 sent on FDDI always have non-zero priority. However, it may be 191 simpler or more useful to transmit all IPv6 packets on FDDI with 192 non-zero priority. 194 5. Stateless Autoconfiguration 196 The interface token [CONF] for an FDDI interface is the EUI-64 197 identifier [EUI64] derived from the interface's built-in 48-bit IEEE 198 802 address. The OUI of the Ethernet address (the first three 199 octets) becomes the company_id of the EUI-64 (the first three 200 octets). The fourth and fifth octets of the EUI are set to the 201 fixed value FFFE hexadecimal. The last three octets of the Ethernet 202 address become the last three octets of the EUI-64. 204 For example, the interface token for an Ethernet interface whose 205 built-in address is, in hexadecimal and in canonical bit order, 207 34-56-78-9A-BC-DE 209 would be 211 34-56-78-FF-FE-9A-BC-DE. 213 A different MAC address set manually or by software should not be 214 used to derive the interface token. 216 An IPv6 address prefix used for stateless autoconfiguration of an 217 FDDI interface must have a length of 64 bits. 219 6. Link-Local Addresses 221 The IPv6 link-local address [AARCH] for an FDDI interface is formed 222 by appending the interface token, as defined above, to the prefix 223 FE80::/64. 225 10 bits 54 bits 64 bits 226 +----------+-----------------------+----------------------------+ 227 |1111111010| (zeros) | Interface Token | 228 +----------+-----------------------+----------------------------+ 230 7. Address Mapping -- Unicast 232 The procedure for mapping IPv6 addresses into FDDI link-layer 233 addresses is described in [DISC]. The Source/Target Link-layer 234 Address option has the following form when the link layer is FDDI. 236 0 1 237 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 239 | Type | Length | 240 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 241 | | 242 +- FDDI -+ 243 | | 244 +- Address -+ 245 | | 246 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 248 Option fields: 250 Type 1 for Source Link-layer address. 251 2 for Target Link-layer address. 253 Length 1 (in units of 8 octets). 255 FDDI Address 256 The 48 bit FDDI IEEE 802 address, in canonical bit 257 order. This is the address the interface currently 258 responds to, and may be different from the built-in 259 address used as the address token. 261 8. Address Mapping -- Multicast 263 An IPv6 packet with a multicast destination address DST, consisting 264 of the sixteen octets DST[1] through DST[16], is transmitted to the 265 FDDI multicast address whose first two octets are the value 3333 266 hexadecimal and whose last four octets are the last four octets of 267 DST. 269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 270 |0 0 1 1 0 0 1 1|0 0 1 1 0 0 1 1| 271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 272 | DST[13] | DST[14] | 273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 274 | DST[15] | DST[16] | 275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 9. Security Considerations 279 Security considerations are not addressed in this memo. 281 10. Acknowledgments 283 Erik Nordmark and Matt Thomas contributed to the method for 284 interaction with bridges. 286 11. References 288 [AARCH] R. Hinden, S. Deering "IP Version 6 Addressing 289 Architecture", RFC 1884. 291 [BRIDGE]ISO/IEC 10038 : 1993 [ANSI/IEEE Std 802.1D] Media access 292 control (MAC) bridges. 294 [CONF] S. Thomson, T. Narten, "IPv6 Stateless Address 295 Autoconfiguration", RFC 1971. 297 [DISC] T. Narten, E. Nordmark, W. A. Simpson, "Neighbor Discovery 298 for IP Version 6 (IPv6)", RFC 1970. 300 [EUI64] "64-Bit Global Identifier Format Tutorial", 301 http://standards.ieee.org/db/oui/tutorials/EUI64.html. 303 [IPV6] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) 304 Specification", RFC 1883. 306 [PMTU] J. Mogul, S. Deering "Path MTU Discovery", RFC 1191. 308 12. Author's Address 310 Matt Crawford 311 Fermilab MS 368 312 PO Box 500 313 Batavia, IL 60510 314 USA 316 Phone: +1 630 840-3461 318 EMail: crawdad@fnal.gov