IPng Working Group Matt Crawford Internet Draft Fermilab September 26, 1997 Transmission of IPv6 Packets over FDDI Networks Status of this Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). Distribution of this memo is unlimited. 1. Introduction This document specifies the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on FDDI networks. It also specifies the content of the Source/Target Link-layer Address option used in Router Solicitation, Router Advertisement, Neighbor Solicitation, Neighbor Advertisement and Redirect messages when those messages are transmitted on an FDDI network. This document replaces RFC 2019, 'Transmission of IPv6 Packets Over FDDI', which will become historic. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [KWORD]. Expires March 26, 1998 Crawford [Page 1] Internet Draft IPv6 Over FDDI September 26, 1997 2. Maximum Transmission Unit FDDI permits a frame length of 4500 octets (9000 symbols), including at least 22 octets (44 symbols) of Data Link encapsulation when long-format addresses are used. Subtracting 8 octets of LLC/SNAP header, this would, in principle, allow the IPv6 [IPV6] packet in the Information field to be up to 4470 octets. However, it is desirable to allow for the variable sizes and possible future extensions of the MAC header and frame status fields. The default MTU size for IPv6 packets on an FDDI network is therefore 4352 octets. This size may be reduced by a Router Advertisement [DISC] containing an MTU option which specifies a smaller MTU, or by manual configuration of each node. If a Router Advertisement received on an FDDI interface has an MTU option specifying an MTU larger than 4352, or larger than a manually configured value, that MTU option may be logged to system management but must be otherwise ignored. For purposes of this document, information received from DHCP is considered "manually configured" and the term FDDI includes CDDI. 3. Frame Format FDDI provides both synchronous and asynchronous transmission, with the latter class further subdivided by the use of restricted and unrestricted tokens. Only asynchronous transmission with unrestricted tokens is required for FDDI interoperability. Accordingly, IPv6 packets shall be sent in asynchronous frames using unrestricted tokens. The robustness principle dictates that nodes should be able to receive synchronous frames and asynchronous frames sent using restricted tokens. IPv6 packets are transmitted in LLC/SNAP frames, using long-format (48 bit) addresses. The data field contains the IPv6 header and payload and is followed by the FDDI Frame Check Sequence, Ending Delimiter, and Frame Status symbols. Expires March 26, 1998 Crawford [Page 2] Internet Draft IPv6 Over FDDI September 26, 1997 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+ | FC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination | +- -+ | FDDI | +- -+ | Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source | +- -+ | FDDI | +- -+ | Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DSAP | SSAP | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CTL | OUI ... | +-+-+-+-+-+-+-+-+ + | ... OUI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ethertype | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 | +- -+ | header | +- -+ | and | +- -+ / payload ... / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (Each tic mark represents one bit.) FDDI Header Fields: FC The Frame Code must be in the range 50 to 57 hexadecimal, inclusive, with the three low order bits indicating the frame priority. The Frame Code should be in the range 51 to 57 hexadecimal, inclusive, for reasons given in the next section. DSAP, SSAP Both the DSAP and SSAP fields shall contain the value AA hexadecimal, indicating SNAP encapsulation. Expires March 26, 1998 Crawford [Page 3] Internet Draft IPv6 Over FDDI September 26, 1997 CTL The Control field shall be set to 03 hexadecimal, indicating Unnumbered Information. OUI The Organizationally Unique Identifier shall be set to 000000 hexadecimal. Ethertype The Ethernet protocol type ("ethertype") shall be set to the value 86DD hexadecimal. 4. Interaction with Bridges 802.1d MAC bridges which connect different media, for example Ethernet and FDDI, have become very widespread. Some of them do IPv4 packet fragmentation and/or support IPv4 Path MTU discovery [PMTU], many others do not, or do so incorrectly. Use of IPv6 in a bridged mixed-media environment must not depend on support from MAC bridges, unless those bridges are known to correctly implement IPv6 Path MTU Discovery [PMTU, ICMPV6]. For correct operation when mixed media are bridged together by bridges which do not support IPv6 Path MTU Discovery, the smallest MTU of all the media must be advertised by routers in an MTU option. If there are no routers present, this MTU must be manually configured in each node which is connected to a medium with a default MTU larger than the smallest MTU. 5. Stateless Autoconfiguration The Interface Identifier [AARCH] for an FDDI interface is based on the EUI-64 identifier [EUI64] derived from the interface's built-in 48-bit IEEE 802 address. The EUI-64 is formed as follows. (Canonical bit order is assumed throughout.) The OUI of the FDDI MAC address (the first three octets) becomes the company_id of the EUI-64 (the first three octets). The fourth and fifth octets of the EUI are set to the fixed value FFFE hexadecimal. The last three octets of the FDDI MAC address become the last three octets of the EUI-64. The Interface Identifier is then formed from the EUI-64 by complementing the "Universal/Local" (U/L) bit, which is the next- to-lowest order bit of the first octet of the EUI-64. For further discussion on this point, see [ETHER] and [AARCH]. For example, the Interface Identifier for an FDDI interface whose built-in address is, in hexadecimal, Expires March 26, 1998 Crawford [Page 4] Internet Draft IPv6 Over FDDI September 26, 1997 34-56-78-9A-BC-DE would be 36-56-78-FF-FE-9A-BC-DE. A different MAC address set manually or by software should not be used to derive the Interface Identifier. If such a MAC address must be used, its global uniqueness property should be reflected in the value of the U/L bit. An IPv6 address prefix used for stateless autoconfiguration [ACONF] of an FDDI interface must have a length of 64 bits. 6. Link-Local Addresses The IPv6 link-local address [AARCH] for an FDDI interface is formed by appending the Interface Identifier, as defined above, to the prefix FE80::/64. 10 bits 54 bits 64 bits +----------+-----------------------+----------------------------+ |1111111010| (zeros) | Interface Identifier | +----------+-----------------------+----------------------------+ 7. Address Mapping -- Unicast The procedure for mapping IPv6 unicast addresses into FDDI link- layer addresses is described in [DISC]. The Source/Target Link- layer Address option has the following form when the link layer is FDDI. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- FDDI -+ | | +- Address -+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Expires March 26, 1998 Crawford [Page 5] Internet Draft IPv6 Over FDDI September 26, 1997 Option fields: Type 1 for Source Link-layer address. 2 for Target Link-layer address. Length 1 (in units of 8 octets). FDDI Address The 48 bit FDDI IEEE 802 address, in canonical bit order. This is the address the interface currently responds to, and may be different from the built-in address used to derive the Interface Identifier. 8. Address Mapping -- Multicast An IPv6 packet with a multicast destination address DST, consisting of the sixteen octets DST[1] through DST[16], is transmitted to the FDDI multicast address whose first two octets are the value 3333 hexadecimal and whose last four octets are the last four octets of DST. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 1 1 0 0 1 1|0 0 1 1 0 0 1 1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DST[13] | DST[14] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DST[15] | DST[16] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 9. Security Considerations The method of derivation of Interface Identifiers from MAC addresses is intended to preserve global uniqueness when possible. However, there is no protection from duplication through accident or forgery. 10. References [AARCH] R. Hinden, S. Deering "IP Version 6 Addressing Architecture", Currently draft-ietf-ipngwg-addr-arch-v2- 02.txt. [ACONF] S. Thomson, T. Narten, "IPv6 Stateless Address Autoconfiguration", currently draft-ietf-ipngwg-addrconf- Expires March 26, 1998 Crawford [Page 6] Internet Draft IPv6 Over FDDI September 26, 1997 v2-00.txt. [DISC] T. Narten, E. Nordmark, W. A. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", currently draft-ietf-ipngwg- discovery-v2-00.txt. [ETHER] M. Crawford, "Transmission of IPv6 Packets over Ethernet Networks", currently draft-ietf-ipngwg-trans-ethernet- 02.txt. [EUI64] "64-Bit Global Identifier Format Tutorial", http://standards.ieee.org/db/oui/tutorials/EUI64.html. [ICMPV6]A. Conta, S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6)", RFC 1885 [IPV6] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", currently draft-ietf-ipngwg-ipv6-spec-v2- 00.txt. [KWORD] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels," RFC 2119. [PMTU] J. Mogul, S. Deering "Path MTU Discovery", RFC 1191. 11. Author's Address Matt Crawford Fermilab MS 368 PO Box 500 Batavia, IL 60510 USA Phone: +1 630 840-3461 EMail: crawdad@fnal.gov Expires March 26, 1998 Crawford [Page 7]