Internet Engineering Task Force Matt Crawford INTERNET-DRAFT Fermilab <draft-ietf-ipngwg-fddi-ntwrks-00.txt> August 15, 1995 A Method for the 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. Introduction This memo specifies the frame format for transmission of IPv6 [IPV6] packets and the method of forming IPv6 link-local addresses on FDDI networks. It also specifies the content of the Source/Target Link- layer Address option used the the Router Solicitation, Router Advertisement, Neighbor Solicitation, and Neighbor Advertisement messages described in [DISC], when those messages are transmitted on an FDDI network. Maximum Transmission Unit Although FDDI permits a frame length of 4500 octets (9000 symbols), including Data Link encapsulation, it is desirable to allow for future extensions to the MAC header and frame status fields. The default MTU size for IPv6 packets on an FDDI network is therefore Crawford Expires February 1996 [Page 1]
INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 15 August 1995 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 is received with an MTU option specifying an MTU larger than 4352, or larger than a manually configured value less than 4352, that MTU option must be ignored. 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. +-------+ ^ | FC | | +-------+-------+-------+-------+-------+-------+ | | Destination FDDI address | | +-------+-------+-------+-------+-------+-------+ FDDI | Source FDDI address | header +-------+-------+-------+-------+-------+-------+ | | DSAP | SSAP | CTL | OUI | | +-------+-------+-------+-------+-------+-------+ | | Ethertype | v +-------+-------+-------+-------+-------+------+------+ | IPv6 header and payload ... / +-------+-------+-------+-------+-------+------+------+ FDDI Header Fields: FC The Frame Code shall be in the range 50 to 57 hexadecimal, inclusive, with the three low order bits indicating the frame priority. Transmission by hosts and routers of frames Crawford Expires February 1996 [Page 2]
INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 15 August 1995 with priority zero (FC =3D 50 hex) is discouraged in order to= aid implementors who wish to distinguish on-ring nodes from off-ring nodes. DSAP, SSAP Both the DSAP and SSAP fields shall contain the value AA hexadecimal, indictating SNAP encapsulation. 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. Stateless Autoconfiguration and Link-Local Addresses The address token [CONF] for an FDDI interface is the interface's built-in 48-bit IEEE 802 address, in canonical bit order. A different MAC address set manually or by software should not be used as the address token. An IPv6 address prefix used for stateless autoconfiguration of an FDDI interface must be 80 bits in length. The IPv6 Link-local address [AARCH] for an FDDI interface is formed by appending the interface's IEEE 802 address to the 80-bit prefix FE80::. +-------+-------+-------+-------+-------+-------+------+------+ | FE 80 00 00 00 00 00 00 | +-------+-------+-------+-------+-------+-------+------+------+ | 00 00 | FDDI Address | +-------+-------+-------+-------+-------+-------+------+------+ Address Mapping -- Unicast The procedure for mapping IPv6 addresses into FDDI link-layer addresses is described in [DISC]. The Source/Target Link-layer Crawford Expires February 1996 [Page 3]
INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 15 August 1995 Address option has the following form when the link layer is FDDI. +-------+-------+-------+-------+-------+-------+------+------+ | Type |Length | FDDI Address | +-------+-------+-------+-------+-------+-------+------+------+ 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. Address Mapping -- Multicast An IPv6 packet with a multicast destination address DST 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, ordered from more to least significant. +-------+-------+-------+-------+-------+-------+ | 33 | 33 | DST13 | DST14 | DST15 | DST16 | +-------+-------+-------+-------+-------+-------+ Open Issues What about subnets bridged together with different MTU? For example, Ethernet and FDDI. This will be addressed in a separate document. Security Considerations Security considerations are not addressed in this memo. Crawford Expires February 1996 [Page 4]
INTERNET-DRAFT Transmission of IPv6 Packets Over FDDI 15 August 1995 References [AARCH] R. Hinden, S. Deering, IP Version 6 Addressing Architecture. Currently draft-ietf-ipngwg-addr-arch-03.txt. [CONF] S. Thomson, IPv6 Stateless Address Autoconfiguration. Currently draft-ietf-addrconf-ipv6-03.txt. [DISC] T. Narten, E. Nordmark, W. A. Simpson, Neighbor Discovery for IP Version 6 (IPv6). Currently draft-ietf-ipngwg-discovery-01.txt. [IPV6] S. Deering, R. Hinden, Internet Protocol, Version 6 (IPv6) Specification. Currently draft-ietf-ipngwg-ipv6-spec-02.txt. Author's Address Matt Crawford Fermilab MS 368 PO Box 500 Batavia, IL 60510 USA Phone: +1 708 840-3461 EMail: crawdad@fnal.gov Crawford Expires February 1996 [Page 5]
