VLAN Aggregation for Efficient IP Address Allocation
RFC 3069

Document Type RFC - Informational (February 2001; Errata)
Last updated 2013-03-02
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Network Working Group                                       D. McPherson
Request for Comments: 3069                          Amber Networks, Inc.
Category: Informational                                         B. Dykes
                                                         Onesecure, Inc.
                                                           February 2001

          VLAN Aggregation for Efficient IP Address Allocation

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 (2001).  All Rights Reserved.

Abstract

   This document introduces the concept of Virtual Local Area Network
   (VLAN) aggregation as it relates to IPv4 address allocation.  A
   mechanism is described by which hosts that reside in the same
   physical switched infrastructure, but separate virtual broadcast
   domains, are addressed from the same IPv4 subnet and share a common
   default gateway IP address, thereby removing the requirement of a
   dedicated IP subnet for each virtual Local Area Network (LAN) or
   Metropolitan Area Network (MAN).

   Employing such a mechanism significantly decreases IPv4 address
   consumption in virtual LANs and MANs.  It may also ease
   administration of IPv4 addresses within the network.

1. Introduction

   The VLAN [802.1Q] aggregation technique described in this document
   provides a mechanism by which hosts that reside within the same
   physical switched infrastructure, but separate virtual broadcast
   domains, may be addressed from the same IPv4 subnet and may share a
   common default gateway IPv4 address.

   Such a mechanism provides several advantages over traditional IPv4
   addressing architectures employed in large switched LANs today.  The
   primary advantage, that of IPv4 address space conservation, can be
   realized when considering the diagram in Figure 1:

McPherson & Dykes            Informational                      [Page 1]
RFC 3069       VLAN Aggregation for IP Address Allocation  February 2001

   Figure 1:

    +------+    +------+    +------+    +------+    +------+
    |      |    |      |    |      |    |      |    |      |
    | A.1  |    | A.2  |    | B.1  |    | C.1  |    | B.2  |
    |      |    |      |    |      |    |      |    |      |
    +------+    +------+    +------+    +------+    +------+
        \          |           |           |            /
          \        |           |           |          /
            \ +-----------------------------------+ /
              |                                   |
              |          Ethernet Switch(es)      |
              |                                   |
              +-----------------------------------+
                               |
                               |
                          +--------+
                          |        |
                          | Router |
                          |        |
                          +--------+

   In the Figure 1 hosts A.1 and A.2 belong to customer A, VLAN A.
   Hosts B.1 and B.2 belong to customer B, VLAN B.  Host C.1 belongs to
   customer C and resides in it's own virtual LAN, VLAN C.

   Traditionally, an IP subnet would be allocated for each customer,
   based on initial IP requirements for address space utilization, as
   well as on projections of future utilization.  For example, a scheme
   such as that illustrated in Table 1 may be used.

   Table 1:
                                Gateway     Usable   Customer
     Customer   IP Subnet       Address     Hosts    Hosts
     ========   ============    =======     ======   ========
     A          1.1.1.0/28      1.1.1.1     14       13
     B          1.1.1.16/29     1.1.1.17    6        5
     C          1.1.1.24/30     1.1.1.25    2        1

   Customer A's initial deployment consists of 2 hosts, though they
   project growth of up to 10 hosts.  As a result, they're allocated the
   IP subnet 1.1.1.0/28 which provides 16 IP addresses.  The first IP
   address, 1.1.1.0, represents the subnetwork number.  The last IP
   address, 1.1.1.15, represents the directed broadcast address.  The
   first usable address of the subnet, 1.1.1.1, is assigned to the
   router and serves as the default gateway IP address for the subnet.
   The customer is left 13 IP addresses, even though their requirement
   was only for 10 IP addresses.

McPherson & Dykes            Informational                      [Page 2]
RFC 3069       VLAN Aggregation for IP Address Allocation  February 2001

   Customer B's initial deployment consists of 2 hosts, though they
   project growth of up to 5 hosts.  As a result, they're allocated the
   IP subnet 1.1.1.16/29 which provides 8 IP addresses.  The first IP
   address, 1.1.1.16, represents the subnetwork number.  The last IP
   address, 1.1.1.23, represents the directed broadcast address.  The
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