IP Multicast over Token-Ring Local Area Networks (RFC1469)
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
This document specifies a method for the transmission of IP multicast datagrams over Token-Ring Local Area Networks. Although an interim solution has emerged and is currently being used, it is the intention of this document to specify a more efficient means of transmission using an assigned Token-Ring functional address.
Network Working Group T. Pusateri
Request for Comments: 1469 Consultant
IP Multicast over Token-Ring Local Area Networks
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet
community, and requests discussion and suggestions for improvements.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
Distribution of this memo is unlimited.
This document specifies a method for the transmission of IP multicast
datagrams over Token-Ring Local Area Networks. Although an interim
solution has emerged and is currently being used, it is the intention
of this document to specify a more efficient means of transmission
using an assigned Token-Ring functional address.
IP multicasting provides a means of transmitting IP datagrams to a
group of hosts. A group IP address is used as the destination
address in the IP datagram as documented in STD 5, RFC 1112 .
These group addresses, also referred to as Class D addresses, fall in
the range from 126.96.36.199 to 188.8.131.52. A standard method of
mapping IP multicast addresses to media types such as ethernet and
fddi exist in  and RFC 1188 . This document attempts to define
the mapping for an IP multicast address to the corresponding Token-
Ring MAC address.
The Token-Ring Network Architecture Reference  provides several
types of addressing mechanisms. These include both individual
(unicast) and group addresses (multicast). A special subtype of
group addresses are called functional addresses and are indicated by
a bit in the destination MAC address. They were designed for widely
used functions such as ring monitoring, NETBIOS, Bridge, and Lan
Manager frames. There are a limited number of functional addresses,
31 in all, and therefore several unrelated functions must share the
same functional address.
It would be most desirable if Token-Ring could use the same mapping
as ethernet and fddi for IP multicast to hardware multicast
addressing. However, current implementations of Token-Ring
controller chips cannot support this. To see why, we must first
examine the Destination MAC address format.
Destination Address Format
The destination MAC address consists of six octets. In the following
diagram of a MAC address, the order of transmission of the octets is
from top to bottom (octet 0 to octet 5), and the order of
transmission of the bits within each octet is from right to left (bit
0 to bit 7). This is the so-called "canonical" bit order for IEEE
802.2 addresses. Addresses supplied to or received from token ring
interfaces are usually laid out in memory with the bits of each octet
in the opposite order from that illustrated, i...