RFC 2019 (rfc2019) - Page 1 of 6

Transmission of IPv6 Packets Over FDDI

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Network Working Group                                        M. Crawford
Request for Comments: 2019                                      Fermilab
Category: Standards Track                                   October 1996



    A Method for the Transmission of IPv6 Packets over FDDI Networks

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Introduction

   This memo specifies the MTU and frame format for transmission of IPv6
   [IPV6] packets on FDDI networks, including a method for MTU
   determination in the presence of 802.1d bridges to other media.  It
   also specifies the method of forming IPv6 link-local addresses on
   FDDI networks and 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

   FDDI permits a frame length of 4500 octets (9000 symbols), including
   at least 22 octets (44 symbols) of Data Link encapsulation when
   long-format addresses are used.  Subtracting 8 octets of LLC/SNAP
   header, this would, in principle, allow the IPv6 packet in the
   Information field to be up to 4470 octets.  However, it is desirable
   to allow for the variable sizes and possible future extensions to the
   MAC header and frame status fields.  The default MTU size for IPv6
   packets on an FDDI network is therefore 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 a
   smaller value on each node.  If a Router Advertisement is received
   with an MTU option specifying an MTU larger than the default or the
   manually configured value, that MTU option may be logged to system
   management but must be otherwise ignored.

   For purposes of this document, information received from DHCP is
   considered "manually configured".





Crawford                    Standards Track
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