One document matched: draft-ietf-ipngwg-token-ring-00.txt
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,
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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.
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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)
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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
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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.
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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
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