Thoughts on Address Resolution for Dual MAC FDDI Networks
RFC 1329

Document Type RFC - Informational (May 1992; No errata)
Updated by RFC 5494
Last updated 2013-03-02
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Network Working Group                                           P. Kuehn
Request for Comments: 1329                                      May 1992

       Thoughts on Address Resolution for Dual MAC FDDI Networks

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard.  Distribution of this memo is

1. Abstract

   In this document an idea is submitted how IP and ARP can be used on
   inhomogeneous FDDI networks (FDDI networks with single MAC and dual
   MAC stations) by introducing a new protocol layer in the protocol
   suite of the dual MAC stations.  Thus two dual MAC stations are able
   to do a load splitting across the two rings and use the double
   bandwidth of 200 Mbits/s as single MAC stations.  The new layer is an
   extension of layer 3.  For the user, the higher layer protocols, IP
   and ARP the property "dual MAC" is transparent.  No modification is
   required in the protocol suite of single MAC stations and transparent

2. Acknowledgements

   This paper is a result of a diploma thesis prepared at the Technical
   University of Munich, Lehrstuhl fuer Kommunikationsnetze, in co-
   operation with the Siemens Nixdorf AG.  The author would like to
   thank Jrg Eberspher and Bernhard Edmaier from the university, Andreas
   Thimmel and Jens Horstmeier from the SNI AG at Augsburg for the
   helpful comments and discussions.

3. Conventions

   Primary MAC, P-MAC           MAC, placed on the primary ring
   Secondary MAC, S-MAC         MAC, placed on the secondary ring
   Inhomogeneous ring           configuration of a dual FDDI ring with
                                single MAC and dual MAC stations

   DMARP                        Dual MAC Address Resolution Protocol

4. Assumptions

   When a dual FDDI ring wraps, both MACs in a dual MAC station are
   assumed to remain connected to the ring.  ANSI is just investigating
   whether the Configuration Management in the Station Management of a

Kuehn                                                           [Page 1]
RFC 1329     Address Resolution for Dual MAC FDDI Networks      May 1992

   FDDI station can be modified to allow this.  According to the FDDI
   SMT standard [1], different addresses are required for all MACs on
   the primary and the secondary ring.

   In this paper, the MAC in a single MAC station is assumed to reside
   on the primary ring.  The application of single MAC stations which
   have their MAC attached to the secondary ring is not precluded, but
   therefor additional connectivity between the two rings is required.
   These configurations are beyond the scope of this document.

5. The Application of Transparent Bridges

   Transparent bridges can provide links to other 802 LANs or further
   inhomogeneous FDDI rings.  The connection between two inhomogeneous
   FDDI rings can be realized by one or two transparent bridges. When
   two transparent bridges are used, one transparent bridge links the
   primary rings, the other the secondary rings.  If two secondary rings
   are connected by a transparent bridge, a path of transparent bridges
   must exist between the two primary rings.  No transparent bridges are
   allowed between the primary and the secondary ring.

6. Protocol Layers in Single MAC Stations

   The new protocol layer, named load sharing layer, is drafted to be
   introduced only in dual MAC stations.  In single MAC stations, IP and
   ARP are working on top of the Subnetwork Access Protocol (SNAP) 04]
   and the Logical Link Control protocol (802.2 LLC) [3].  LLC type 1 is
   used because connectionless services are investigated only.

Kuehn                                                           [Page 2]
RFC 1329     Address Resolution for Dual MAC FDDI Networks      May 1992

      |   IP                     |
      |   ARP                    |
       |             |
       | ARP frames  | IP frames
       |             |
      |   SNAP                   |
      |   LLC                    |
      |   FDDI-MAC               || F     |
      +--------------------------+| D  S  |
      +--------------------------+| D  M  |
      |   FDDI PHY and PMD       || I  T  |

   For the ARP layer, the following model is assumed:
   |  - ARP entity -                                       |           |
   |                                                       | IP frames |
   | +----------------+   +----------------+ read          |           |
   | | Cache          |   |                | entries +-------------+   |
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