Customizing DHCP Configuration on the Basis of Network Topology
RFC 7969

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Internet Engineering Task Force (IETF)                          T. Lemon
Request for Comments: 7969                                 Nominum, Inc.
Category: Informational                                     T. Mrugalski
ISSN: 2070-1721                                                      ISC
                                                            October 2016

    Customizing DHCP Configuration on the Basis of Network Topology

Abstract

   DHCP servers have evolved over the years to provide significant
   functionality beyond that described in the DHCP base specifications.
   One aspect of this functionality is support for context-specific
   configuration information.  This memo describes some such features
   and explains their operation.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7969.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Lemon & Mrugalski             Informational                     [Page 1]
RFC 7969               DHCP Topology Customization          October 2016

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Identifying Client's Location by DHCP Servers . . . . . . . .   3
     3.1.  DHCPv4-Specific Behavior  . . . . . . . . . . . . . . . .   7
     3.2.  DHCPv6-Specific Behavior  . . . . . . . . . . . . . . . .   7
   4.  Simple Subnetted Network  . . . . . . . . . . . . . . . . . .  10
   5.  Relay Agent Running on a Host . . . . . . . . . . . . . . . .  12
   6.  Cascaded Relays . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  Regional Configuration Example  . . . . . . . . . . . . . . .  13
   8.  Multiple Subnets on the Same Link . . . . . . . . . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     10.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   The DHCPv4 [RFC2131] and DHCPv6 [RFC3315] protocol specifications
   describe how addresses can be allocated to clients based on network
   topology information provided by the DHCP relay infrastructure.
   Address allocation decisions are integral to the allocation of
   addresses and prefixes in DHCP.

   The DHCP protocol also describes mechanisms for provisioning devices
   with additional configuration information, for example, DNS [RFC1034]
   server addresses, default DNS search domains, and similar
   information.

   Although it was the intent of the authors of these specifications
   that DHCP servers would provision devices with configuration
   information appropriate to each device's location on the network,
   this practice was never documented, much less described in detail.

   Existing DHCP server implementations do in fact provide such
   capabilities; the goal of this document is to describe those
   capabilities for the benefit of both operators and protocol designers
   who may wish to use DHCP as a means for configuring their own
   services but may not be aware of the capabilities provided by most
   modern DHCP servers.

Lemon & Mrugalski             Informational                     [Page 2]
RFC 7969               DHCP Topology Customization          October 2016

2.  Terminology

   o  CPE device: Customer Premise Equipment device.  Typically a router
      belonging to the customer that connects directly to the provider
      link.