Internet DRAFT - draft-cadar-dhc-dhcpv6-v4options
draft-cadar-dhc-dhcpv6-v4options
Network Working Group C. Cadar
Internet-Draft NEC (Netlab)
Expires: August 9, 2004 C. Strauf
JOIN (WWU)
February 9, 2004
DHCPv6 IPv4 Information Options
draft-cadar-dhc-dhcpv6-v4options-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on August 9, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
To ease the management of a site, the Dynamic Host Configuration
Protocol (DHCP) is often used. DHCP exists both for the Internet
Protocol Version 4 (DHCPv4 for IPv4) and Version 6 (DHCPv6 for IPv6).
To avoid possible pitfalls that occur if both DHCP versions are used
and to avoid redundancy, IPv4 Information Options may be transmitted
using DHCPv6 as described in this document. In dual-stack IPv4/IPv6
scenarios that employ DHCPv6, DHCPv4 can be completely replaced by
using the DHCPv6 IPv4 Information Options.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements notation & Naming Conventions . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Simultaneous DHCPv6 & DHCPv4: Issues . . . . . . . . . . . . . 7
5. Prerequisites & Scenarios . . . . . . . . . . . . . . . . . . 8
6. Integrating DHCPv4 options into DHCPv6 . . . . . . . . . . . . 9
7. State Machine/Protocol Machinery . . . . . . . . . . . . . . . 10
8. IPv4 Information Option Message Format . . . . . . . . . . . . 11
8.1 IPv4 Address Option . . . . . . . . . . . . . . . . . . . . . 11
8.2 The Broadcast Address Option . . . . . . . . . . . . . . . . . 11
8.3 IPv4 Netmask Option . . . . . . . . . . . . . . . . . . . . . 12
8.4 IPv4 Router Option . . . . . . . . . . . . . . . . . . . . . . 12
8.5 The Host Name Option . . . . . . . . . . . . . . . . . . . . . 13
8.6 World Wide Web Server Option . . . . . . . . . . . . . . . . . 14
8.7 IPv4 DNS Servers & Search Domains . . . . . . . . . . . . . . 14
8.8 IPv4 Forwarding Enable/Disable Option . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . 20
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1. Introduction
The Dynamic Host Configuration Protocol (DHCP) is used in both
domains of IPv4 and IPv6 to configure hosts automatically. Currently
DHCP for IPv4 (DHCPv4) [RFC2131] and DHCP for IPv6 (DHCPv6) [RFC3315]
are defined and deployed. One phase during the transition from IPv4
to IPv6 can be the deployment of IPv4 and IPv6 at the same time
("dual-stack"). In particular, a host in a specific broadcast domain
has both IPv4 and IPv6 connectivity on the same port and has both an
IPv4 and IPv6 stack provided by its operating system. Networks
running IPv4 or IPv6 protocol use either DHCPv4 or DHCPv6, but
running both version of DHCP in parallel may cause problems that are
going to be identified in this document. Hosts being configured
using both mechanisms at the same time may end up with a non-useful
configuration.
This document discusses the integration of DHCPv4 functionality into
DHCPv6, and so enabling the configuration of both address domains
with a single dynamic host configuration protocol. This is achieved
by adapting DHCPv4 options to DHCPv6 option format and by using
existing DHCPv6 transport mechanisms.
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2. Requirements notation & Naming Conventions
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 [RFC2119].
The following conventions and abbreviations will be used within this
document:
o "DHCPv4" denotes the Dynamic Host Configuration Protocol according
to [RFC2131].
o "DHCPv6" denotes the Dynamic Host Configuration Protocol according
to [RFC3315].
o "Dual-stack" networks provide both IPv4 and IPv6 connectivity to
hosts.
o "Dual-stack" hosts have both IPv4 and IPv6 stacks in their
operating system and both stacks are enabled.
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3. Overview
The Dynamic Host Configuration Protocol is a common management tool
to automatically configure clients in a particular site without the
need of the administrator's interaction. This configuration includes
but is not limited to IP addresses, default routers (IPv4) and
netmasks (IPv4). DHCPv4 or DHCPv6 are the transport and exchange
protocols for this information. DHCP is not only used for large
sites. It is also commonly used in SOHO sites e.g. on small broadband
access routers to automatically configure clients that are attached
to the local network. There are two, in some scenarios three
different components in DHCP exchanges: there are always a client and
a server involved. In some sites, there also exist relay agents that
relay DHCP messages between different broadcast domains. However,
relay agents do not alter the information conveyed with the DHCP
protocols and hence do not need special attention in this document.
As stated before, there are two different DHCP standards: DHCPv4 and
DHCPv6. Both exist independently, and DHCPv6 is not backward
compatible with regards to the protocol. The message and option sizes
differ and the client identification is handled in a different way
(DHCPv4 uses MAC addresses to identify a client, DHCPv6 uses DHCP
Unique Identifiers (DUIDs) and Identity Association Identifiers
(IAIDs)). In theory, both DHCP versions could exist in parallel in
the same site and a host may be both a DHCPv4 and DHCPv6 client. But
there are certain pitfalls described in Section 4, which complicate
this co-existence. Therefore it is convenient in a number of
scenarios that are identified in Section 5 to use either DHCPv4 or
DHCPv6 but not both on the same host. This is only possible if DHCPv6
is capable of transporting information that is normally transported
using DHCPv4. The purpose of this document is to present a practical
solution to this problem by defining DHCPv6 options that contain IPv4
information. Choosing DHCPv6 over DHCPv4 instead of DHCPv4 over
DHCPv6 is done for the following reasons:
o DHCPv6 is more sophisticated in a number of ways (authentication,
identification of clients, etc.)
o DHCPv6 options can easily be adapted to hold IPv4 information
o New DHCPv6 options are easily created to convey IPv4 information
o The client's identity is independent of the client's hardware. A
change of the MAC address of a client has no impact on the
client's identity stored on the server
It is important to note that this document does not introduce
backward compatibility to DHCPv4 in DHCPv6 on the protocol level. The
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state machinery and option format of DHCPv6 stays untouched and fully
compliant with [RFC3315]. Furthermore, it is not the intention of
this document to render DHCPv4 obsolete e.g. in IPv4-only sites.
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4. Simultaneous DHCPv6 & DHCPv4: Issues
Issues that occur when employing DHCPv4 and DHCPv6 simultaneously are
identified in the document: "IPv4 and IPv6 Dual-Stack Issues for
DHCPv6", T. Chown, S. Venaas, C. Strauf, February 2004,
draft-chown-dhc-dual-stack-00 (work in progress).
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5. Prerequisites & Scenarios
To use DHCPv6 IPv4 Information Options, the following prerequisites
must be met:
o A DHCPv6 client MUST have both IPv4 and IPv6 stacks in their
operating systems. IPv4 Information Options MUST NOT be used if an
IPv4 stack is not present.
o A DHCPv6 client that requests IPv4 Information Options SHOULD NOT
additionally use DHCPv4.
o Neither DHCPv6-clients nor -servers that use IPv4 Information
Options need to ensure the existence of IPv4 connectivity.
The usage of IPv4 Information Options is the preferred method of
providing IPv4 information to clients in a dual-stack network where
DHCPv6 is deployed. In such dual-stack networks, the following
differentiation is made:
1. IPv4-only clients that use DHCPv4.
2. Dual-stack or IPv6-only clients that use DHCPv6.
Dual-stack clients that use DHCPv6 SHOULD NOT additionally use
DHCPv4. Instead, IPv4 Information Options SHOULD be requested using
DHCPv6. Information like IPv4 address, IPv4 netmask and IPv4 default
router is then transmitted using DHCPv6 transport. DHCPv6 can even be
used if no global IPv6 connectivity is present but site scoped IPv6
multicast addresses can be used by clients to contact DHCPv6 servers.
Contrary to DHCPv4, MAC addresses are not used to identify a client.
Instead, the DHCP Unique Identifier (DUID) and Identity Association
Identifier (IAID) as defined in [RFC3315] are used in the usual
manner for all DHCPv6 exchanges. This reduces the overhead of
managing MAC addresses additionally to DUID and IAID.
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6. Integrating DHCPv4 options into DHCPv6
There are two ways of integrating IPv4 specific options into DHCPv6.
Existing DHCPv4 options can be converted to match the DHCPv6 option
format or existing DHCPv6 options can be modified to transport IPv4
information. The latter method is preferred if DHCPv6 offers more
convenient management methods or if it facilitates the option's
implementation. In every case, a new option code needs to be assigned
by the IANA.
For DHCPv6 options, the address field that normally carries IPv6
addresses can be reduced from a 128 bits to a 32 bits length. Other
IPv6 specific parts also need to be adjusted.
DHCPv4 options need to be reworked to fit the DHCPv6 option format.
The modified DHCPv4 options can be put into a different context in
some cases, e.g. as a sub-option of another option. The necessity for
this has to be decided for each case.
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7. State Machine/Protocol Machinery
The impact of introducing IPv4 options in the DHCPv6 protocol stack
is minimal. The OPTION_IAADDR_IPv4 option MAY be encapsulated in a
IA_NA or IA_TA option and its behavior is the same as for IA Address
Option described in [RFC3315]. As for the other options they MAY be
requested by the clients using the Option Request option described in
Section 22.7 of [RFC3315]. The IPv6 address lifetime extension
procedure described in [RFC3315] applies to IPv4 addresses as well,
the other IPv4 related options, such as DNS and Default Routers, MUST
be included in the RENEW/REBIND messages, the IAADDR_IPv4 option
containing the IPv4 address for renewal MAY coexist together with an
IPv6 IAADDR option in the same IA_TA or IA_NA option of the DHCPv6
message. On reception of an IA option which contains both
OPTION_IAADDR option and an OPTION_IAADDR_IPv4 option, the client
SHOULD process both options by attaching the IPv6 address to the IPv6
stack of the interface it was intended to and the IPv4 address to its
IPv4 stack of the same interface. Also, if the client requested the
DNS option the server SHOULD send a DNS server address list
containing the DNS servers in order of preference; the list MAY
contain both IPv6 addresses and IPv4 addresses in the form of IPv6
compatibility addresses. The server MAY change the IPv4/IPv6
addresses and/or DNS settings of the client at any moment with the
RECONFIGURE message. Message relaying SHOULD use IPv6 addresses only
as described in [RFC3315].
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8. IPv4 Information Option Message Format
8.1 IPv4 Address Option
The IAADDR_IPv4 option must be embedded in an IA_NA or IA_TA field as
defined in [RFC3315], sections 22.4 and 22.5. The OPTION_IAADDR_IPv4
is depicted in Figure 1.
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_IAADDR_IPv4 | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| preferred-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. IAaddr-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: OPTION_IAADDR_IPv4
option-code: OPTION_IAADDR_IPv4.
option-len: 24 + length of IAaddr-options field.
IPv4 address: An IPv4 address.
preferred-lifetime: The preferred lifetime for the IPv4 address in
the option, expressed in units of seconds.
valid-lifetime: The valid lifetime for the IPv4 address in the
option, expressed in units of seconds.
IAaddr-options: Options associated with this address.
8.2 The Broadcast Address Option
The IAaddr-options address field of OPTION_IAADDR_IPv4 MAY contain a
broadcast options related to the specified IPv4 address. This option
specifies the broadcast address in use on the client's subnet
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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_BROADCAST | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| broadcast-address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: OPTION_BROADCAST
option-code: OPTION_BROADCAST.
option-len: 4 octets.
broadcast-address: The specification of the broadcast address given
by the server.
8.3 IPv4 Netmask Option
The IAaddr-options address field of OPTION_IAADDR_IPv4 may contain a
netmask options related to the specified IPv4 address:
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_NETMASK | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Netmask-address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: OPTION_NETMASK
option-code: OPTION_NETMASK.
option-len: 4.
Netmask-address: The netmask for the IPv4 address.
8.4 IPv4 Router Option
The router option specifies a list of IP addresses for routers on the
client's subnet. Routers SHOULD be listed in order of preference.
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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_ROUTER | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ................ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: OPTION_ROUTER
option-code: OPTION_ROUTER.
option-len: 4*(number of router addresses).
Router-address: Address of the router for the IAID.
8.5 The Host Name Option
This option specifies the name of the client. The name may or may not
be qualified with the local domain name. See [RFC1035] for character
set restrictions. The format of the Host Name option is:
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_HOST_NAME | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| hostname |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: OPTION_HOST_NAME
option-code: OPTION_HOST_NAME.
option-len: Length of the "hostname" field in octets.
hostname: The specification of the host name given by the server.
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8.6 World Wide Web Server Option
The WWW server option specifies a list of WWW available to the
client. Servers SHOULD be listed in order of preference.
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_WWW | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| server-address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| server-address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ................ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: OPTION_WWW
option-code: OPTION_WWW.
option-len: 4*(number of server addresses).
server-address: The server address.
8.7 IPv4 DNS Servers & Search Domains
The DNS Configuration options described in [RFC3646] may be used to
carry IPv4 addresses in the form of IPv6 compatibility addresses in
OPTION_DNS_SERVERS. The DHCPv6 client should convert IPv6
compatibility addresses back to IPv4 addresses on reception before
using them for configuration purposes. This is mandatory on host
operating systems that cannot handle IPv6 compatibility addresses.
All search domains that are necessary for normal operation can be
transmitted using OPTION_DOMAIN_LIST in [RFC3646]. No additional
client modifications or interactions are necessary.
8.8 IPv4 Forwarding Enable/Disable Option
This option specifies whether the client should configure its IPv4
layer for packet forwarding. A value of 0 means disable IP
forwarding, and a value of 1 means enable IP forwarding.
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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_FORWARDING | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| value |
+-+-+-+-+-+-+-+-+
Figure 7: OPTION_FORWARDING
option-code: OPTION_FORWARDING.
option-len: 1 octet.
value Value of Forwarding Enable/Disable Option.
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9. Security Considerations
There are no additional or other security considerations than already
mentioned in [RFC3315] and [RFC3646].
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10. IANA Considerations
The Internet Assigned Numbers Authority (IANA) needs to assign
numbers to the following option codes from the DHCP option code space
defined in section "IANA Considerations" of [RFC3315]:
o OPTION_IAADDR_IPv4
o OPTION_NETMASK
o OPTION_ROUTER
o OPTION_HOST_NAME
o OPTION_FORWARDING
o OPTION_BROADCAST
o OPTION_WWW
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11. Acknowledgments
The authors would like to thank the following individuals for their
input and comments (no particular order): Martin Stiemerling (NEC),
Juergen Quittek (NEC), Christian Schild (JOIN), Tina Strauf (JOIN),
Andre Stolze (JOIN), Ralph Droms (Cisco), Gunther Van de Velde
(Cisco), Tim Chown (University of Southampton), Stig Venaas
(UNINETT).
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References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
M. Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[RFC3646] Droms, R., "DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
December 2003.
Authors' Addresses
Cristian Cadar
Netlab, NEC Europe Ltd.
Kurfuersten-Anlage 36
Heidelberg D-69115
DE
EMail: cristian.cadar@netlab.nec.de
URI: http://www.netlab.nec.de
Christian Strauf
JOIN (University of Muenster)
Roentgenstr. 9-13
Muenster D-48149
DE
EMail: strauf@uni-muenster.de
URI: http://www.join.uni-muenster.de
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