MAC-Forced Forwarding: A Method for Subscriber Separation on an Ethernet Access Network
RFC 4562

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Network Working Group                                          T. Melsen
Request for Comments: 4562                                      S. Blake
Category: Informational                                         Ericsson
                                                               June 2006

                         MAC-Forced Forwarding:
    A Method for Subscriber Separation on an Ethernet Access Network

Status of This Memo

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

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes a mechanism to ensure layer-2 separation of
   Local Area Network (LAN) stations accessing an IPv4 gateway over a
   bridged Ethernet segment.

   The mechanism - called "MAC-Forced Forwarding" - implements an
   Address Resolution Protocol (ARP) proxy function that prohibits
   Ethernet Media Access Control (MAC) address resolution between hosts
   located within the same IPv4 subnet but at different customer
   premises, and in effect directs all upstream traffic to an IPv4
   gateway.  The IPv4 gateway provides IP-layer connectivity between
   these same hosts.

Melsen & Blake               Informational                      [Page 1]
RFC 4562                 MAC-Forced Forwarding                 June 2006

Table of Contents

   1. Introduction ....................................................2
      1.1. Access Network Requirements ................................3
      1.2. Using Ethernet as an Access Network Technology .............4
   2. Terminology .....................................................5
   3. Solution Aspects ................................................6
      3.1. Obtaining the IP and MAC Addresses of the Access Routers ...6
      3.2. Responding to ARP Requests .................................7
      3.3. Filtering Upstream Traffic .................................8
      3.4. Restricted Access to Application Servers ...................8
   4. Access Router Considerations ....................................8
   5. Resiliency Considerations .......................................9
   6. Multicast Considerations ........................................9
   7. IPv6 Considerations ............................................10
   8. Security Considerations ........................................10
   9. Acknowledgements ...............................................11
   10. References ....................................................11
      10.1. Normative References .....................................11
      10.2. Informative References ...................................12

1.  Introduction

   The main purpose of an access network is to provide connectivity
   between customer hosts and service provider access routers (ARs),
   typically offering reachability to the Internet and other IP networks
   and/or IP-based applications.

   An access network may be decomposed into a subscriber line part and
   an aggregation network part.  The subscriber line - often referred to
   as "the first mile" - is characterized by an individual physical (or
   logical, in the case of some wireless technologies) connection to
   each customer premises.  The aggregation network - "the second mile"
   - performs aggregation and concentration of customer traffic.

   The subscriber line and the aggregation network are interconnected by
   an Access Node (AN).  Thus, the AN constitutes the border between
   individual subscriber lines and the common aggregation network.  This
   is illustrated in the following figure.

Melsen & Blake               Informational                      [Page 2]
RFC 4562                 MAC-Forced Forwarding                 June 2006

        Access       Aggregation  Access    Subscriber    Customer
        Routers      Network      Nodes     Lines         Premises
                                                          Networks
        +----+           |
      --+ AR +-----------|        +----+
        +----+           |        |    +----------------[]--------
                         |--------+ AN |
                         |        |    +----------------[]--------
                         |        +----+
                         |
                         |        +----+
                         |        |    +----------------[]--------
                         |--------+ AN |
                         |        |    +----------------[]--------
                         |        +----+
                         |
                         |        +----+
                         |        |    +----------------[]--------
                         |--------+ AN |
        +----+           |        |    +----------------[]--------
      --+ AR +-----------|        +----+
        +----+           |

1.1.  Access Network Requirements