Transmission of IPv6 Packets over FDDI Networks
obsoletes
- rfc-2019 — Transmission of IPv6 Packets Over FDDI
updated by
- rfc-8064 — Recommendation on Stable IPv6 Interface Identifiers
Extracted elements (21)
RFC 2467 obsoletes RFC 2019 with three functional changes: removal of 'FDDI adjacency detection' (due to IEEE 802.1p work), replacement of the 48-bit Address Token with the 64-bit EUI-64-based Interface Identifier, and shortening of the autoconfiguration prefix from 80 to 64 bits.
The default MTU of 4352 is chosen conservatively below the theoretical maximum of 4470 to accommodate variable sizes and possible future extensions of the MAC header and frame status fields, rather than using the largest possible value.
For purposes of this document, information received from DHCP is considered 'manually configured', and the term FDDI includes CDDI (copper-based FDDI).
A manually or software-set MAC address should not be used to derive the Interface Identifier. If such an 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 of an FDDI interface must have a length of 64 bits.
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.
IPv6 packets shall be sent in asynchronous frames using unrestricted tokens. Nodes should also be able to receive synchronous frames and asynchronous frames sent using restricted tokens (robustness principle).
The 48-bit FDDI address in the Source/Target Link-layer Address option is the address the interface currently responds to and may differ from the built-in address used to derive the Interface Identifier.
The default MTU size for IPv6 packets on an FDDI network is 4352 octets. This is smaller than the theoretical maximum of 4470 octets to allow for variable sizes and possible future extensions of the MAC header and frame status fields.
The DSAP and SSAP fields shall both be set to AA hexadecimal (indicating SNAP encapsulation), and the CTL field shall be set to 03 hexadecimal (Unnumbered Information).
The Interface Identifier is 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.
The OUI field in the LLC/SNAP header shall be set to 000000 hexadecimal, and the Ethertype shall be set to 86DD hexadecimal to identify IPv6.
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.
When mixed media are bridged together by bridges that do not support IPv6 Path MTU Discovery, the smallest MTU of all the media must be advertised by routers in an MTU option. If no routers are present, this MTU must be manually configured in each node connected to a medium with a default MTU larger than the smallest MTU.
An IPv6 packet with a multicast destination address DST is transmitted to the FDDI multicast address whose first two octets are 3333 hexadecimal and whose last four octets are the last four octets of DST (DST[13]–DST[16]).
The Frame Code (FC) field must be in the range 50 to 57 hexadecimal inclusive, with the three low-order bits indicating the frame priority.
The Interface Identifier for an FDDI interface is derived from the EUI-64 identifier formed from the 48-bit IEEE 802 MAC address: the OUI (first 3 octets) becomes the company_id, octets 4–5 are set to FFFE hexadecimal, and the last 3 octets of the MAC address become the last 3 octets of the EUI-64.
The IPv6 link-local address for an FDDI interface is formed by appending the 64-bit Interface Identifier to the prefix FE80::/64 (10 bits 1111111010 followed by 54 zero bits).
The method of deriving Interface Identifiers from MAC addresses is intended to preserve global uniqueness when possible. However, there is no protection from duplication through accident or forgery.
IPv6 packets are transmitted in LLC/SNAP frames using long-format (48-bit) FDDI addresses. The frame contains FC, Destination Address (48-bit), Source Address (48-bit), DSAP, SSAP, CTL, OUI (3 octets), Ethertype, and IPv6 header and payload.
The Source/Target Link-layer Address option for FDDI has a Type field (1=source, 2=target), a Length field of 1 (in units of 8 octets), and a 48-bit FDDI IEEE 802 address in canonical bit order.