Internet Engineering Task Force Stephen Thomas INTERNET DRAFT AT&T Tridom <draft-ietf-ipngwg-token-ring-00.txt> August 24, 1995 A Method for the Transmission of IPv6 Packets over Token Ring 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 Token Ring networks [8025]. 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 a Token Ring. IPv6 Encapsulation IPv6 packets are transmitted in LLC/SNAP frames, using long-format (48 bit) addresses. The data field contains the IPv6 header and payload. The following figure shows a complete IPv6 frame. Thomas Expires February 1996 [Page 1]
INTERNET-DRAFT IPv6 over Token Ring August 24, 1995 +-------+-------+-------+-------+ | SD | AC | FC | | +-----------------------+ | | Destination Address | | +-----------------------+ | | Source | +-------+ Address +-------+ | | DSAP | +-------+-------+-------+-------+ | SSAP | CTL | OUI | +-------+-------+-------+-------+ | OUI | EtherType | | +-------+---------------+ | | | ~ IPv6 header and payload... ~ | | +-------------------------------+ | FCS | +-------+-------+---------------+ | ED | FS | +-------+-------+ In the presence of source route bridges, a routing information field (RIF) may appear immediately after the source address. A RIF is present in frames when the most signficant bit of the source address is set to one. Token Ring Header Fields SD - Starting Delimiter AC - Access Control FC - Frame Control Destination Address - 48-bit IEEE address of destination station Source Address - 48-bit IEEE address of source station DSAP - Destination Service Access Point (for LLC/SNAP format, shall always contain the value 0xAA) SSAP - Source Service Access Point (for LLC/SNAP format, shall always contain the value 0xAA) CTL - Control Field (for Unnumbered Information, shall always contain the value 0x03) Thomas Expires February 1996 [Page 2]
INTERNET-DRAFT IPv6 over Token Ring August 24, 1995 OUI - Organizationally Unique Identifier (for EtherType encoding, shall always contain the value 0x000000) EtherType - Protocol type of encapsulated payload (for IPv6, shall always contain the value 0x86DD) FCS - Frame Check Sequence ED - Ending Delimiter FS - Frame Status Maximum Transmission Unit IEEE 802.5 networks have a maximum packet size based on the maximum time a node may hold the token. This time depends on many factors including the data signalling rate and the number of nodes on the ring. The determination of maximum packet size becomes even more complex when multi-ring networks with bridges are considered. The possible ranges for MTU sizes are 256-4472 octets (for 4 Mbit/s rings) and 256-17800 octets (for 16 Mbit/s rings). This variation suggests that implementations must rely on static configuration or router advertisements [DISC] to determine actual MTU sizes. Common default values include 2002 octets (4 Mbit/s rings) and 8188 octets (16 Mbit/s rings). In a environment using source route bridging, the process of discovering the MAC-level route to a neighbor can yield the MTU for the path to that neighbor. The information is contained in the largest frame subfield of the routing information field. The following table lists the possible values of that subfield, and the IPv6 MTU size that results. If an implementation uses this information to determine MTU sizes, it must maintain separate MTU values for each neighbor. LF (binary) MAC MTU IP MTU 000 552 508 001 1064 1020 010 2088 2044 011 4136 4092 100 8232 8188 Thomas Expires February 1996 [Page 3]
INTERNET-DRAFT IPv6 over Token Ring August 24, 1995 Stateless Autoconfiguration and Link-local Addresses The address token [CONF] for a Token Ring 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 a Token Ring interface must be 80 bits in length. The IPv6 Link-local address [AARCH] for a Token Ring 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 | | +-------+-------+ | | Token Ring Address | +-------+-------+-------+-------+ Address Mapping - Unicast The procedure for mapping IPv6 addresses into Token Ring link layer addresses is described in [DISC]. The Source/Target Link Layer Address option has the following form when the link layer is Token Ring. +-------+-------+-------+-------+ | Type |Length | | +-------+-------+ | | Token Ring Address | +-------+-------+-------+-------+ Option Fields: Type 1 for Source Link Layer Address 2 for Target Link Layer Address Length 1 (in units of 8 octets) Token Ring Address The 48-bit IEEE 802 address, in canonical bit order. Thomas Expires February 1996 [Page 4]
INTERNET-DRAFT IPv6 over Token Ring August 24, 1995 Address Mapping - Multicast All IPv6 packets with multicast destination addresses are transmitted to the Token Ring functional address 03-00-00-20-00-00 (in canonical form). Note that protocols other than IPv6 may use this same functional address, so all frames destined to this address are not guaranteed to be IPv6 packets. Security Considerations Security considerations are not addressed in this memo. References [8025] IEEE Standards for Local Area Networks: Token Ring Access Method and Physical Layer Specifications. IEEE Std 802.5-1989. [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 Stephen Thomas AT&T Tridom Phone: (770) 514-3522 840 Franklin Court Fax: (770) 514-3491 Marietta, GA 30067 USA Email: stephen.thomas@tridom.com Thomas Expires February 1996 [Page 5]
