DHCPv6 class based prefix
draft-bhandari-dhc-class-based-prefix-05

Abstract

This document introduces options to communicate property and associate meta data with prefixes. It extends DHCPv6 prefix delegation and address allocation using the meta data for selection of prefixes and addresses.

Status of This Memo

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Copyright Notice

Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 1.1. Motivation
• 1.1.1. Mobile networks
• 1.1.2. Home networks
• 1.2. Terminology
• 1.3. Requirements Language
• 2. Overview
• 2.1. Prefix Property and Class Options
• 2.2. Consideration for different DHCPv6 entities
• 2.2.1. Requesting Router Behavior for IA_PD allocation
• 2.2.2. Delegating Router Behavior for IA_PD allocation
• 2.2.3. DHCPv6 Client Behavior for IA_NA allocation
• 2.2.4. DHCPv6 Server Behavior for IA_NA allocation
• 2.3. Usage
• 2.3.1. Class based prefix and IA_NA allocation
• 2.3.2. Class based prefix and IA_PD allocation
• 2.3.3. Class based prefix and SLAAC
• 2.3.4. Class based prefix and applications
• 3. Example Application
• 3.1. Mobile gateway example
• 3.1.1. Class based prefix delegation
• 3.1.2. IPv6 address assignment from class based prefix
• 3.2. Homenet Example
• 3.2.1. Class based prefix delegation to the HGW
• 3.2.2. IPv6 Assignment to Homenet hosts using stateful DHCPv6
• 4. Acknowledgements
• 5. Contributors
• 6. IANA Considerations
• 6.1. OPTION_PREFIX_PROPERTY values
• 7. Security Considerations
• 8. Change History (to be removed prior to publication as an RFC)
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Authors' Addresses

1. Introduction

In IPv6 a network interface can acquire multiple addresses from the same scope. In such a multi-prefix network each of the multiple prefixes can have a specific property and purpose associated with it. Example: In a mobile network a mobile device can be assigned a prefix from its home network and another from the visiting network that it is attached to. Another example is a prefix may provide free Internet access without offering any quality of service guarantees while another prefix may be charged along with providing quality of service guarantees for network service access. A prefix can have well defined properties that is universal and have a meta data associated with it that communicates its local significance. The properties and meta data of prefix will be relevant for prefix delegation, source address selection as elaborated in the subsequent sections.

This document defines OPTION_PREFIX_PROPERTY option that communicates property of the prefix that is universally understood. This document defines OPTION_PREFIX_CLASS option to communicate meta data of the prefix that communicates the prefix's local significance.

This document discusses usage of OPTION_PREFIX_CLASS to request and select prefixes with specific meta data via IA_PD and IA_NA as defined in [RFC3633] and[RFC3315] respectively. This document defines the behavior of the DHCPv6 server, the DHCPv6 prefix requesting router and the DHCPv6 client to use OPTION_PREFIX_CLASS option for requesting and selecting prefixes and addresses.

The network address can be configured via DHCPv6 as defined in [RFC3315] or via Stateless Address Autoconfiguration (SLAAC) as defined in [RFC4862], additional information of a prefix can be provided via DHCPv6 or via IPv6 Router Advertisement (RA). The information provided in the options defined in this document OPTION_PREFIX_PROPERTY and OPTION_PREFIX_CLASS can be used for source address selection. Communicated property and meta data information about the prefix via IPv6 Router Advertisement (RA) will be dealt with in separate document [I-D.korhonen-6man-prefix-properties].

1.1. Motivation

In this section motivation for class based prefix delegation that qualifies the delegated prefix with additional class information is described in the context of mobile networks and home networks. The property information attached to a delegated prefix helps to distinguish a delegated IPv6 prefix and selection of the prefix by different applications using it.

1.1.1. Mobile networks

In the mobile network architecture, there is a mobile router which functions as a IP network gateway and provides IP connectivity to mobile nodes. Mobile router can be the requesting router requesting delegated IPv6 prefix using DHCPv6. Mobile router can assume the role of DHCPv6 server for mobile nodes(DHCPv6 clients) attached to it. A mobile node in mobile network architecture can be associated with multiple IPv6 prefixes belonging to different domains for e.g. home address prefix, care of address prefix as specified in [RFC3775].

The delegated prefixes when seen from the mobile router perspective appear to be like any other prefix, but each prefixes have different meta data referred to as "Prefix Color" in the mobile networks. Some delegated prefixes may be topologically local and some may be remote prefixes anchored on a global anchor, but available to the local anchor by means of tunnel setup in the network between the local and global anchor. Some may be local with low latency characteristics suitable for voice call break-out, some may have global mobility support. So, the prefixes have different properties and it is required for the application using the prefix to learn about this property in order to use it intelligently. There is currently no semantics in DHCPv6 prefix delegation that can carry this information to specify properties of a delegated prefix. In this scenario, the mobile router is unable to further delegate a longer prefix intelligently based on properties of the prefix learnt. Neither is a mobile device able to learn about the property of the prefix assigned to influence source address selection. Example to determine if the prefix is a home address or care of address.

1.1.2. Home networks

In a fixed network environment, the homenet CPE may also function as both a DHCPv6 client (requesting the IA_PD(s)) and a DHCPv6 server allocating prefixes from delegated prefix(es) to downstream home network hosts. Some service providers may wish to delegate multiple prefixes to the CPE for use by different services classes and traffic types.

Motivations for this include:

• Using source prefix to identify the service class / traffic type that is being transported. The source prefix may then reliably be used as a parameter for differentiated services or other purposes. E.g. [I-D.jiang-v6ops-semantic-prefix]
• Using the specific source prefix as a host identifier for other services. E.g. as an input parameter to a DHCPv4 over IPv6 server [I-D.ietf-dhc-dhcpv4-over-ipv6]

To meet these requirements, when the CPE (functioning as a DHCPv6 server) receives an IA_NA or IA_TA request from a homenet host, a mechanism is required so that the correct prefix for requested service class can be selected for allocation. Likewise for DHCPv6 clients located in the homenet, a mechanism is necessary so that the intended service class for a requested prefix can be signalled to the DHCPv6 server.

1.2. Terminology

This document uses the terminology defined in [RFC2460], [RFC3315] and [RFC3633].

1.3. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

2. Overview

This section defines prefix property and prefix class options in IA_PD and IA_NA. This section defines the behavior of the delegating router, the requesting router and the DHCPv6 client. It discusses these options in the context of a DHCPv6 information request from a DHCPv6 client to a DHCPv6 server.

2.1. Prefix Property and Class Options

The format of the DHCPv6 prefix property and prefix class options are shown below.

   
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      OPTION_PREFIX_PROPERTY   |         option-length(2)      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Properties        |                 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code:       OPTION_PREFIX_PROPERTY (TBD1)
   option-length:     2 
   Properties:        16 bits  maintained as
                      OPTION_PREFIX_PROPERTY in 
                      IANA registered namespace.
                      Each value in the registry represents a property.
                      Multiple properties can be represented by bitwise
                      ORing of the individual property values in this
                      field.
      
 

Prefix Property Option

Along with the OPTION_PREFIX_PROPERTY a meta data associated with the prefix that is of local relevance is communicated using OPTION_PREFIX_CLASS defined below:

  
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    OPTION_PREFIX_CLASS      |          option-length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Prefix Class           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   
   option-code:          OPTION_PREFIX_CLASS (TBD2)
   option-length:        2     
   Prefix Class:         16 bit integer with the integer value
                         of local significance.
  

Prefix Class Option

2.2. Consideration for different DHCPv6 entities

The model of operation of communicating prefixes to be used by a DHCPv6 server is as follows. A requesting router requests prefix(es) from the delegating router, as described in Section 2.2.1. A delegating router is provided IPv6 prefixes to be delegated to the requesting router. Examples of ways in which the delegating router is provided these prefixes are:

• Configuration
• Prefix delegated via a DHCPv6 request to another DHCPv6 server
• Using a Authentication Authorization Accounting (AAA) protocol like RADIUS [RFC2865]

The delegating router chooses prefix(es) for delegation, and responds with prefix(es) to the requesting router along with additional options in the allocated prefix as described in Section 2.2.2. The requesting router is then responsible for the delegated prefix(es) after the DHCPv6 REQUEST message exchange. For example, the requesting router may create DHCPv6 server configuration pools from the delegated prefix, and function as a DHCPv6 Server. When the requesting router then receives a DHCPv6 IA_NA requests it can select the address to be allocated based on the OPTION_PREFIX_CLASS option received in IA_NA request or any of the other method as described in Section 2.3.1.

2.2.1. Requesting Router Behavior for IA_PD allocation

DHCPv6 requesting router can request for prefixes in the following ways:

• In the SOLICIT message within the IA_PD Prefix option, it MAY include OPTION_PREFIX_CLASS requesting prefix delegation for the specific class indicated in the OPTION_PREFIX_CLASS option. It can include multiple IA_PD Prefix options to indicate it's preference for more than one prefix class. The class of prefix it requests is learnt via configuration or any other out of band mechanism not defined in this document.
• In the SOLICIT message include an OPTION_ORO option with the OPTION_PREFIX_CLASS option code to request prefixes from all the classes that the DHCPv6 server can provide to this requesting Router.

The requesting router parses the OPTION_PREFIX_CLASS option in the OPTION_IAPREFIX option area of the corresponding IA_PD Prefix option in the ADVERTISE message. The Requesting router MUST then include all or subset of the received class based prefix(es) in the REQUEST message so that it will be responsible for the prefixes selected.

The requesting router parses and stores OPTION_PREFIX_PROPERTY if received with the prefix.

2.2.2. Delegating Router Behavior for IA_PD allocation

If the Delegating router supports class based prefix allocation by supporting the OPTION_PREFIX_CLASS option and it is configured to assign prefixes from different classes, it selects prefixes for class based prefix allocation in the following way:

• If requesting router includes OPTION_PREFIX_CLASS within the IA_PD Prefix option, it selects prefixes to be offered from that specific class.
• If requesting router includes OPTION_PREFIX_CLASS within OPTION_ORO, then based on its configuration and policy it MAY offer prefixes from multiple classes available.

The delegating router responds with an ADVERTISE message after populating the IP_PD option with prefixes from different classes. Along with including the IA_PD prefix options in the IA_PD option, it MAY include the OPTION_PREFIX_CLASS option in the OPTION_IAPREFIX option area of the corresponding IA_PD prefix option with the class information of the prefix.

If neither the OPTION_ORO nor the IA_PD option in the SOLICIT message include the OPTION_PREFIX_CLASS option, then the delegating router MAY allocate the prefix as specified in [RFC3633] without including the class option in the IA_PD prefix option in the response.

If OPTION_ORO option in the Solicit message includes the OPTION_PREFIX_CLASS option code but the delegating router does not support the solution described in this specification, then the delegating router acts as specified in [RFC3633]. The requesting router MUST in this case also fall back to the behavior specified in [RFC3633].

If both delegating and requesting routers support class-based prefix allocation, but the delegating router cannot offer prefixes for any other reason, it MUST respond to requesting router with appropriate status code as specified in [RFC3633]. For e.g., if no prefixes are available in the specified class then the delegating router MUST include the status code NoPrefixAvail in the response message.

In addition if the delegating router has additional property associated with the prefix it will be provided in OPTION_PREFIX_PROPERTY option.

2.2.3. DHCPv6 Client Behavior for IA_NA allocation

DHCPv6 client MAY request for an IA_NA address allocation from a specific prefix class in the following way:

• In the SOLICIT message within the IA_NA option, it MAY include the OPTION_PREFIX_CLASS requesting address to be allocated from a specific class indicated in that option. The class information to be requested can be learnt via configuration or any other out of band mechanism not described in this document.

If DHCPv6 client receives OPTION_PREFIX_CLASS, OPTION_PREFIX_PROPERTY options in the IAaddr-options area of the corresponding IA_NA but does not support one or both of these options, it SHOULD ignore the received option(s).

2.2.4. DHCPv6 Server Behavior for IA_NA allocation

The DHCPv6 server parses OPTION_PREFIX_CLASS option received and when it supports allocation within the requested OPTION_PREFIX_CLASS responds with an ADVERTISE message after populating the IA_NA option with address information from the requested prefix class. Along with including the IA Address options in the IA_NA option, it also includes the OPTION_PREFIX_CLASS option in the corresponding IAaddr-options area.

Even though the IA_NA option in the SOLICIT message does not include the OPTION_PREFIX_CLASS option, based on local policies, the DHCP server MAY select a default OPTION_PREFIX_CLASS value for the client and then SHOULD include the OPTION_PREFIX_CLASS option in the IAaddr-options area of the corresponding IA_NA it sends to the client. If both DHCP client and server support class based address allocation, but the DHCP server cannot offer addresses in the specified Usage class then the DHCP server MUST include the status code NoAddrsAvail (as defined in [RFC3315]) in the response message. If the DHCP server cannot offer addresses for any other reason, it MUST respond to client with appropriate status code as specified in [RFC3315]. In addition if the server has additional property associated with the prefix by means of configuration or learnt from DHCPv6 prefix delegation or derived via any other means it MUST be sent as OPTION_PREFIX_PROPERTY option.

2.3. Usage

Class based prefix delegation can be used by the requesting router to configure itself as a DHCPv6 server to serve its DHCPv6 clients. It can allocate longer prefixes from a delegated shorter prefix it received, for serving IA_NA and IA_PD requests. Prefix property and class can be used for source address selection by applications using the prefix for communication.

2.3.1. Class based prefix and IA_NA allocation

The requesting router can use the delegated prefix(es) from different classes (for example "video" (1), "guest"(2), "voice" (3) etc), for assigning the IPv6 addresses to the end hosts through DHCPv6 IA_NA based on a preconfigured mapping with OPTION_PREFIX_CLASS option, the following conditions MAY be observed:

• It MAY have a pre-configured mapping between the prefix class and OPTION_USER_CLASS option received in IA_NA.
• It MAY match the OPTION_PREFIX_CLASS if the IA_NA request received contains OPTION_PREFIX_CLASS.
• It MAY have a pre-configured mapping between the prefix class and the client DUID received in DHCPv6 message.
• It MAY have a pre-configured mapping between the prefix class and its network interface on which the IA_NA request was received.

The requesting router playing the role of a DHCPv6 server can ADVERTISE IA_NA from a class of prefix(es) thus selected.

2.3.2. Class based prefix and IA_PD allocation

If the requesting router, receives prefix(es) for different classes (for example "video"(1), "guest"(2), "voice"(3) etc), it can use these prefix(es) for assigning the longer IPv6 prefixes to requesting routers it serves through DHCPv6 IA_PD by assuming the role of delegating router, its behavior is explained in Section 2.2.2.

2.3.3. Class based prefix and SLAAC

DHCPv6 IA_NA and IPv6 Stateless Address Autoconfiguration (SLAAC as defined in [RFC4862]) are two ways by IPv6 addresses can be dynamically assigned to end hosts. Making SLAAC class aware is outside the scope of this document, it is specified in [I-D.korhonen-6man-prefix-properties].

2.3.4. Class based prefix and applications

Applications within a host can do source address selection based on the class of the prefix learnt in OPTION_PREFIX_PROPERTY and OPTION_PREFIX_CLASS using rules defined in [RFC6724]. The internal data structure and interface for source address selection used by application to choose source prefix with specific property and class in a host is beyond the scope of this document.

3. Example Application

3.1. Mobile gateway example

The following sub-sections provide examples of class based prefix delegation and how it is used in a mobile network. Each of the examples will refer to the below network:

The example network consists of :

Mobile Gateway It is network entity anchoring IP traffic in the mobile core network. This entity allocates an IP address which is topologically valid in the mobile network and may act as a mobility anchor if handover between mobile and Wi-Fi is supported.

Mobile Nodes (MN) A host or router that changes its point of attachment from one network or subnetwork to another. A mobile node may change its location without changing its IP address; it may continue to communicate with other Internet nodes at any location using its (constant) IP address, assuming link-layer connectivity to a point of attachment is available.

Access Point (AP) A wireless access point, identified by a MAC address, providing service to the wired network for wireless nodes.

Access Router (AR) An IP router residing in an access network and connected to one or more Access Point(AP)s. An AR offers IP connectivity to MNs.

WLAN controller (WLC) The entity that provides the centralized forwarding, routing function for the user traffic.

       _----_           _----_           _----_
     _(      )_       _(      )_       _(      )_
    (Operator-1)     (Operator-2)     (Operator-3)
     (_      _)       (_      _)       (_      _)
        -+--             -+--            '-+--'
    +--------+       +--------+       +--------+
    | Mobile |       | Mobile |       | Mobile |
    |gateway |       |gateway |       |gateway |
    +--------+       +--------+       +--------+
         |                |                |
         +-------------.  |  .-------------+
                       |  |  |
                       |  |  |
                       |  |  |P1:"global-anchor"(1)
                       |  |  |
                     +--------+                        _----_
  +---+              |        |P2:"local-breakout"(2)_(      )_
  |AAA|. . . . . . . | Access |---------------------( Internet )
  +---+              | Aggreg |-----------+          (_      _)
                     | Gateway| P3:"guest"|            '----'
                     +--------+           |
                         |   |             +----- Guest Access 
                         |   |                      Network
                         |   +-------------+
                         |                 |
                         |              +-----+
                         |              | AR  |
                      +-----+           +-----+
                      | WLC |        * ---------*
                      |     |        (    LAN    )
                      +-----+        * ---------*
                      /    \             /    \
                   +----+  +----+     +----+  +----+
                   |WiFi|  |WiFi|     |WiFi|  |WiFi|
                   | AP |  | AP |     | AP |  | AP |
                   +----+  +----+     +----+  +----+
                     .                  .
                    / \                / \
                  MN1 MN2            MN3 MN4(guest)

 +-----------+    _----+----_      +----------+
 |Application|  _(           )_    | Video on |
 |central    |-(   Internet    )---|  Demand  |       
 |           |  (_           _)    |  Service |
 +-----------+    '----+----'      +----------+
                       |
                  _----+----_     +----------+       \
                _(           )_   |ISP Video |        \
              (Service Provider)--| on Demand|         \
                (_  Network  _)   | Service  |         |  ISP
                  '----+----'     +----------+         |  Network
                       |                               |
                +------+-----+                         |
                | Delegating |                         |
                |   Router   |                         |
                +------+-----+                         |
                       |                               |
                       | Customer                      |
                       | Internet connection           /
                       |                              /
                       |                             /
                +------+--------+  ^                 \
                |     IPv6      |  | DHCPv6 Client    \
                | Home gateway  |                      \
                |  Device (CPE) |  | DHCPv6 Server     |
                +------+--------+  v                   |  Home
                       |                               |  Network
          Home Network |                               |
                 +-----+-------+                       |
                 |             |                       |
            +----+-----+ +-----+----+                  |
            |IPv6 Host | |IPv6 Host |                  |
            | (Set top | |   (PC)   |  DHCPv6 Clients  /
            |    box)  | |          |                 /
            +----------+ +----------+                /