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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 1884 (ref. 'AARCH') (Obsoleted by RFC 2373) == Outdated reference: A later version (-06) exists of draft-ietf-ipngwg-discovery-05 ** Obsolete normative reference: RFC 1883 (ref. 'IPV6') (Obsoleted by RFC 2460) Summary: 11 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Engineering Task Force Matt Crawford 2 INTERNET-DRAFT Fermilab 3 February 26, 1996 5 A Method for the Transmission of IPv6 Packets over FDDI Networks 7 Status of this Memo 9 This document is an Internet Draft. Internet Drafts are working 10 documents of the Internet Engineering Task Force (IETF), its Areas, 11 and its Working Groups. Note that other groups may also distribute 12 working documents as Internet Drafts. 14 Internet Drafts are draft documents valid for a maximum of six 15 months. Internet Drafts may be updated, replaced, or obsoleted by 16 other documents at any time. It is not appropriate to use Internet 17 Drafts as reference material or to cite them other than as a "working 18 draft" or "work in progress." 20 To learn the current status of any Internet-Draft, please check the 21 ``1id-abstracts.txt'' listing contained in the Internet Drafts Shadow 22 Directories on ds.internic.net (US East Coast), nic.nordu.net 23 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 24 Rim). 26 Distribution of this memo is unlimited. 28 Introduction 30 This memo specifies the MTU and frame format for transmission of IPv6 31 [IPV6] packets on FDDI networks, including a method for MTU 32 determination in the presence of 802.1d bridges to other media. It 33 also specifies the method of forming IPv6 link-local addresses on 34 FDDI networks and the content of the Source/Target Link-layer Address 35 option used the the Router Solicitation, Router Advertisement, 36 Neighbor Solicitation, and Neighbor Advertisement messages described 37 in [DISC], when those messages are transmitted on an FDDI network. 39 Maximum Transmission Unit 41 FDDI permits a frame length of 4500 octets (9000 symbols), including 42 at least 22 octets (44 symbols) of Data Link encapsulation when 43 long-format addresses are used. Subtracting 8 octets of LLC/SNAP 45 INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 1996-02-26 47 header, this would, in principle, allow the IPv6 packet in the 48 Information field to be up to 4470 octets. However, it is desirable 49 to allow for the variable sizes and possible future extensions to the 50 MAC header and frame status fields. The default MTU size for IPv6 51 packets on an FDDI network is therefore 4352 octets. This size may 52 be reduced by a Router Advertisement [DISC] containing an MTU option 53 which specifies a smaller MTU, or by manual configuration of a 54 smaller value on each node. If a Router Advertisement is received 55 with an MTU option specifying an MTU larger than the default or the 56 manually configured value, that MTU option may be logged to system 57 management but must be otherwise ignored. 59 For purposes of this document, information received from DHCP is 60 considered ``manually configured''. 62 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 +-------+ ^ 79 | FC | | 80 +-------+-------+-------+-------+-------+-------+ | 81 | Destination FDDI address | | 82 +-------+-------+-------+-------+-------+-------+ FDDI 83 | Source FDDI address | header 84 +-------+-------+-------+-------+-------+-------+ | 85 | DSAP | SSAP | CTL | OUI | | 86 +-------+-------+-------+-------+-------+-------+ | 87 | Ethertype | v 88 +-------+-------+-------+-------+-------+------+------+ 89 | IPv6 header and payload ... / 90 +-------+-------+-------+-------+-------+------+------+ 92 INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 1996-02-26 94 FDDI Header Fields: 96 FC The Frame Code must be in the range 50 to 57 hexadecimal, 97 inclusive, with the three low order bits indicating the 98 frame priority. The Frame Code should be in the range 51 to 99 57 hexadecimal, inclusive, for reasons given in the next 100 section. 102 DSAP, SSAP Both the DSAP and SSAP fields shall contain the value AA 103 hexadecimal, indictating SNAP encapsulation. 105 CTL The Control field shall be set to 03 hexadecimal, indicating 106 Unnumbered Information. 108 OUI The Organizationally Unique Identifier shall be set to 109 000000 hexadecimal. 111 Ethertype The ethernet protocol type ("ethertype") shall be set to the 112 value 86DD hexadecimal. 114 Interaction with Bridges 116 For correct operation when mixed media are bridged together, the 117 smallest MTU of all the media must be manually configured in each 118 node or advertised by routers in an MTU option. Nodes transmitting 119 IPv6 on FDDI should implement the following simple mechanism for 120 ``FDDI adjacency detection''. 122 If a node N1 receives, in an FDDI frame with a non-zero LLC priority, 123 a valid Router Advertisement, Neighbor Advertisement, or Neighbor 124 Solicitation from a node N2, then N1 may send unicast IPv6 packets to 125 N2 with sizes up to the default IPv6 FDDI MTU (4352 octets), 126 regardless of any smaller MTU configured manually or received in a 127 Router Advertisement MTU option. N2 may be the IPv6 destination or 128 the next hop router to the destination. 130 Nodes implementing FDDI adjacency detection must provide a 131 configuration option to disable the mechanism. This option may be 132 used when a smaller MTU is desired for reasons other than mixed-media 133 bridging. By default, FDDI adjacency detection should be enabled. 135 The only contemplated use of the LLC priority field of the FC octet 136 is to aid in per-destination MTU determination. It would be 137 sufficient for that purpose to require only that Router 138 Advertisements, Neighbor Advertisements, and Neighbor Solicitations 139 sent on FDDI always have non-zero priority. However, it may be 140 simpler or more useful to transmit all IPv6 packets on FDDI with 142 INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 1996-02-26 144 non-zero priority. 146 Stateless Autoconfiguration and Link-Local Addresses 148 The address token [CONF] for an FDDI interface is the interface's 149 built-in 48-bit IEEE 802 address, in canonical bit order and with the 150 octet in the same order in which they would appear in the header of 151 an ethernet frame. (The individual/group bit is in the first octet 152 and the OUI is in the first three octets.) A different MAC address 153 set manually or by software should not be used as the address token. 155 An IPv6 address prefix used for stateless autoconfiguration of an 156 FDDI interface must be 80 bits in length. 158 The IPv6 Link-local address [AARCH] for an FDDI interface is formed 159 by appending the interface's IEEE 802 address to the 80-bit prefix 160 FE80::. 162 +-------+-------+-------+-------+-------+-------+------+------+ 163 | FE 80 00 00 00 00 00 00 | 164 +-------+-------+-------+-------+-------+-------+------+------+ 165 | 00 00 | FDDI Address | 166 +-------+-------+-------+-------+-------+-------+------+------+ 168 Address Mapping -- Unicast 170 The procedure for mapping IPv6 addresses into FDDI link-layer 171 addresses is described in [DISC]. The Source/Target Link-layer 172 Address option has the following form when the link layer is FDDI. 174 +-------+-------+-------+-------+-------+-------+------+------+ 175 | Type |Length | FDDI Address | 176 +-------+-------+-------+-------+-------+-------+------+------+ 178 Option fields: 180 Type 1 for Source Link-layer address. 181 2 for Target Link-layer address. 183 Length 1 (in units of 8 octets). 185 FDDI Address 186 The 48 bit FDDI IEEE 802 address, in canonical bit order. 187 This is the address the interface currently responds to, and 188 may be different from the built-in address used as the 190 INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 1996-02-26 192 address token. 194 Address Mapping -- Multicast 196 An IPv6 packet with a multicast destination address DST is 197 transmitted to the FDDI multicast address whose first two octets are 198 the value 3333 hexadecimal and whose last four octets are the last 199 four octets of DST, ordered from more to least significant. 201 +-------+-------+-------+-------+-------+-------+ 202 | 33 | 33 | DST13 | DST14 | DST15 | DST16 | 203 +-------+-------+-------+-------+-------+-------+ 205 Security Considerations 207 Security considerations are not addressed in this memo. 209 Acknowledgments 211 Erik Nordmark contributed to the method for interaction with bridges. 213 References 215 [AARCH] R. Hinden, S. Deering, IP Version 6 Addressing Architecture. 216 RFC1884. 218 [CONF] S. Thomson, IPv6 Stateless Address Autoconfiguration. Currently 219 draft-ietf-addrconf-ipv6-auto-07.txt. 221 [DISC] T. Narten, E. Nordmark, W. A. Simpson, Neighbor Discovery for IP 222 Version 6 (IPv6). Currently draft-ietf-ipngwg-discovery-05.txt. 224 [IPV6] S. Deering, R. Hinden, Internet Protocol, Version 6 (IPv6) 225 Specification. RFC1883. 227 INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 1996-02-26 229 Author's Address 231 Matt Crawford 232 Fermilab MS 368 233 PO Box 500 234 Batavia, IL 60510 235 USA 237 Phone: +1 708 840-3461 239 EMail: crawdad@fnal.gov