Provisioning IPv4 Configuration Over IPv6 Only Networks
draft-ietf-dhc-v4configuration-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
|
|
|---|---|---|---|
| Authors | Branimir Rajtar, Ian Farrer | ||
| Last updated | 2013-12-06 | ||
| Replaces | draft-rajtar-dhc-v4configuration | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Tomek Mrugalski | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-dhc-v4configuration-03
DHC WG B. Rajtar
Internet-Draft Hrvatski Telekom
Intended status: Informational I. Farrer
Expires: June 9, 2014 Deutsche Telekom AG
December 06, 2013
Provisioning IPv4 Configuration Over IPv6 Only Networks
draft-ietf-dhc-v4configuration-03
Abstract
As IPv6 becomes more widely adopted, some service providers are
choosing to deploy IPv6 only networks without dual-stack
functionality for IPv4. However, as access to IPv4 based services
will continue to be a requirement for the foreseeable future, IPv4
over IPv6 mechanisms, such as softwire tunnels are being developed.
In order to provision end-user's hosts with the IPv4 configuration
necessary for such mechanisms, a number of different approaches have
been proposed. This memo discusses each of the proposals, identifies
the benefits and drawbacks and recommends a single approach as the
basis for future deployment and development.
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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 9, 2014.
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Copyright Notice
Copyright (c) 2013 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
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview of IPv4 Parameter Configuration Approaches . . . 4
1.2. DHCPv4o6 Based Provisioning - Functional Overview . . . . 5
1.3. DHCPv6 Based Provisioning - Functional Overview . . . . . 6
1.4. DHCPv6 + Stateless DHCPv4oSW Based Provisioning -
Functional Overview . . . . . . . . . . . . . . . . . . . 6
1.5. DHCPv4oSW Based Provisioning - Functional Overview . . . 7
1.6. DHCPv4oDHCPv6 Based Provisioning - Functional Overview . 8
2. Requirements for the Solution Evaluation . . . . . . . . . . 9
3. Comparison of the Five Approaches . . . . . . . . . . . . . . 10
3.1. DHCPv4o6 Based Provisioning . . . . . . . . . . . . . . . 10
3.1.1. Pros . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.2. Cons . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. DHCPv6 Based Provisioning . . . . . . . . . . . . . . . . 11
3.2.1. Pros . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.2. Cons . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. DHCPv6 + Stateless DHCPv4oSW Based Provisioning . . . . . 12
3.3.1. Pros . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.2. Cons . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4. DHCPv4oSW Based Provisioning . . . . . . . . . . . . . . 13
3.4.1. Pros . . . . . . . . . . . . . . . . . . . . . . . . 13
3.4.2. Cons . . . . . . . . . . . . . . . . . . . . . . . . 13
3.5. DHCPv4oDHCPv6 Based Provisioning . . . . . . . . . . . . 14
3.5.1. Pros . . . . . . . . . . . . . . . . . . . . . . . . 14
3.5.2. Cons . . . . . . . . . . . . . . . . . . . . . . . . 14
4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 14
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6.1. DHCPv4oIPv6 . . . . . . . . . . . . . . . . . . . . . . . 15
6.2. DHCPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.3. DHCPv6+DHCPv4oSW . . . . . . . . . . . . . . . . . . . . 15
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6.4. DHCPv4oSW . . . . . . . . . . . . . . . . . . . . . . . . 15
6.5. DHCPv4oDHCPv6 . . . . . . . . . . . . . . . . . . . . . . 16
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
A service provider with an IPv6-only network must also be able to
provide customers with access to the IPv4 Internet and other
IPv4-only services. IPv4 over IPv6 tunneling / translation
mechanisms are an obvious example of this, such as the ones described
in:
o [I-D.ietf-softwire-lw4over6]
o [I-D.ietf-softwire-map]
o [I-D.ietf-softwire-map-t]
In todays home networks, each residential user is allocated a single
global IPv4 address which is used for NAT44. Decentralizing NAT44
allows for much better scaling and, when combined with stateless
network functions, can simplify redundancy and logging. This results
in the need to provision a number of configuration parameters to the
CPE, such as the external public IPv4 address and a restricted port-
range to use for NAT. Other parameters may also be necessary,
depending on the underlying transport technology that is in use. In
IPv4 only networks, DHCPv4 has often been used to provide IPv4
configuration, but in an IPv6 only network, DHCPv4 messages cannot be
transported natively.
For the most simple IPv4 provisioning case, where the client only
needs to receive a static IPv4 address assignment (with no dynamic
address leasing or additional IPv4 configuration), DHCPv6 based
approaches (e.g. [I-D.ietf-softwire-map-dhcp]) may provide a suitable
solution.
This document is concerned with more complex IPv4 configuration
scenarios, to bring IPv4 configuration over IPv6-only networks in
line with the functionality offered by DHCPv4 in IPv4 native
networks. DHCPv4 options may also need to be conveyed to clients for
configuring IPv4 based services, e.g. SIP server addresses.
Although IPv4-in-IPv6 softwire tunnel and translation clients are
currently the only use-case for DHCP based configuration of IPv4
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parameters in IPv6 only networks, a suitable approach must not be
limited to only supporting softwires configuration or be reliant on
specific underlying IPv4 over IPv6 architectures or mechanisms.
This document describes and compares five different methods which
have been proposed as solutions to this problem.
1.1. Overview of IPv4 Parameter Configuration Approaches
The following approaches for transporting IPv4 configuration
parameters over IPv6 only networks have been suggested:
1. Adapt DHCPv4 format messages to be transported over IPv6 as
described in [I-D.ietf-dhc-dhcpv4-over-ipv6]. For brevity, this
is referred to as DHCPv4o6.
2. Extend DHCPv6 to support IPv4 address leasing and other DHCPv4
options.
3. Use DHCPv6 as above for external IPv4 address and source port
configuration. Use DHCPv4 over IPv4 messages within an IPv6
softwire for configuring additional parameters. This is referred
to as DHCPv6 + Stateless DHCPv4oSW.
4. Use DHCPv4 over IPv4 messages transported over a broadcast
capable IPv4overIPv6 transport (e.g. a softwire) for all IPv4
configuration including the external IPv4 address and source port
configuration. This is referred to as DHCPv4oSW.
5. Use DHCPv4 format messages, transporting them within a new DHCPv6
message type as described in [I-D.ietf-dhc-dhcpv4-over-dhcpv6].
This is referred to as DHCPv4oDHCPv6.
At the time of writing, working examples of the first two methods
have been developed and successfully tested in several different
operators networks. The fourth approach has been tested successfully
in a lab environment. The remaining two methods are still
theoretical.
The following sections provide describe each of the approaches in
more detail.
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1.2. DHCPv4o6 Based Provisioning - Functional Overview
In order to receive IPv4 configuration parameters, IPv4-only clients
initiate and exchange DHCPv4 messages with the DHCPv4 server. To
adapt this for an IPv6-only network, an existing DHCPv4 client
implements a 'Host Client Relay' (HCRA) function, which takes DHCPv4
messages and puts them into UDPv6 and IPv6.
As the mechanism involves unicast based communications, the IPv6
address of the server must be provisioned to the client. This option
is described in [I-D.mrugalski-softwire-dhcpv4-over-v6-option].
The IPv6 Transport Server (TSV) provides an IPv6 interface to the
client. This interface may be directly on the server and/or via an
intermediary 'Transport Relay Agent' (TRA) device acting as the
gateway between the IPv4 and IPv6 domains.
For the dynamic allocation of IPv4 addresses, the DHCPv4 server
function needs to be extended to add DHCPv4o6 TSV capabilities, such
as the storing the IPv6 address of DHCPv4o6 clients and implementing
the CRA6ADDR option.
This approach currently uses functional elements for ingress and
egress of the IPv6-only transport domain - the HCRA on the host and
the TRA or TSV on the server. As a result, this approach has
sometimes been referred to as a tunneling approach. However, relay
agent encapsulation is not a tunnel, since it carries only DHCP
traffic; it would be more accurate to describe it as an encapsulation
based transport.
[I-D.ietf-dhc-dhcpv4-over-ipv6] also defines an On-Link Client Relay
agent (LCRA), which is a Client Relay Agent located on the same link
as an unmodified DHCPv4 client. It is worth noting that there is no
technical reason for using relay encapsulation for DHCPv4o6; this
approach was taken because the authors of the draft originally
imagined that it might be used to provide configuration information
for an unmodified DHCPv4 client. However, this turns out not to be a
viable approach: in order for this to work, there would have to be
IPv4 routing on the local link to which the client is connected. In
that case, there's no need for DHCPv4o6.
Given that this is the case, there is no technical reason why
DHCPv4o6 can't simply use the IPv6 transport directly, without any
relay encapsulation. This would greatly simplify the specification
and the implementation, and would still address the requirements
stated in this document.
[I-D.ietf-dhc-dhcpv4-over-ipv6] describes this solution in detail.
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The protocol stack is as follows:
DHCPv4/UDPv6/IPv6
1.3. DHCPv6 Based Provisioning - Functional Overview
In this approach, DHCPv6 [RFC3315] would be extended with new DHCPv6
options for configuring all IPv4 based services and functions (i.e.
IPv4 address assignment and any necessary DHCPv4 options). DHCPv4
options needed by IPv4 clients connected to the IPv6 network are
updated as new DHCPv6 native options carrying IPv4 configuration
parameters. IPv4 address leasing would also need to be managed by
the DHCPv6 server.
At the time of writing, it is not known which or how many such
options would need to be ported from DHCPv4 to DHCPv6.
The protocol stack is as follows:
DHCPv6/UDPv6/IPv6
1.4. DHCPv6 + Stateless DHCPv4oSW Based Provisioning - Functional
Overview
In this approach, the configuration of IPv4 address and source ports
(if required) is carried out using DHCPv6, e.g. using
[I-D.ietf-softwire-map-dhcp]. Any additional IPv4 configuration
parameters which are required are then provisioned using DHCPv4
messages transported within IPv6 in the configured softwire in the
same manner as any other IPv4 based traffic. Broadcast based DHCPv4
DHCPDISCOVER messages (necessary for IPv4 address assignment) can not
be transported as they are not compatible with the softwire
architecture.
On receipt by the tunnel concentrator (e.g. MAP Border Router or a
Lightweight 4over6 lwAFTR), the DHCPv4 message is removed from the
softwire and forwarded to the DHCPv4 server in the same way as any
other IPv4 packet is handled.
As the client is already configured with its external IPv4 address
and source ports (using DHCPv6 or a well-known IPv4 address for DS-
Lite clients), the messages exchanged between the DHCPv4 client and
server would be strictly DHCPINFORM/DHCPACK messages. These would be
used for the configuration of any additional IPv4 parameters.
For this approach to function, a mechanism for the DHCPv4 client to
learn the IPv4 address of the DHCPv4 server is also required. This
could be via a well-known IPv4 address for the DHCPv4 server, a
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DHCPv4 relay function within the tunnel concentrator or other
methods.
From a transport perspective, the key difference between this method
and DHCPv4o6 (described above) is the protocol stack. Here the
DHCPv4 message is first put into UDPv4 and IPv4 and then into the
IPv6 softwire, instead of placing the DHCPv4 message directly into
UDPv6 and IPv6.
Currently, this approach is only theoretical and does not have a
corresponding Internet Draft providing more detail.
The protocol stack used for obtaining an IPv4 address and source
ports (if required) is as follows:
DHCPv6/UDPv6/IPv6
The protocol stack used for obtaining additional IPv4 configuration
is as follows:
DHCPv4/UDPv4/IPv4/IPv6
1.5. DHCPv4oSW Based Provisioning - Functional Overview
[I-D.troan-dhc-dhcpv4osw] describes a method for complete client
configuration using DHCPv4 transported across a broadcast capable
link layer transport, such as a softwire. It differs from stateless
DHCPv6+DHCPv4oSW in that it is capable of supporting all DHCPv4
message types and is not limited solely to DHCPINFORM/DHCPACK
messages. This means that it is also suitable the assignment of IPv4
addresses as well as other DHCPv4 options.
Functionally, a DHCPv4 client operates on the link layer interface
(e.g. the softwire tunnel interface). As the link layer must support
broadcasts, DHCPDISCOVER and other broadcast DHCPv4 messages can be
transported. The DHCPv4 message flow is then the same as described
in section 3.1 of [RFC2131].
In this approach, either the tunnel concentrator must also be the
DHCPv4 server or it must act as a DHCPv4 relay. This allows
broadcast DHCPDISCOVER/DHCPREQUEST messages to be decapsulated and
forwarded to the DHCPv4 server. If the concentrator is functioning
as a relay, then the DHCPv4 Relay Information Option (option 82) is
used to convey the client's source IPv6 address. This is also used
by the relay for routing return DHCPv4 packets.
A DHCPv4oSW client may be configured with a shared IPv4 address with
restricted layer 4 source ports. This will normally exclude the
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well-known TCP/UDP ports in the range 0-1023, so the UDPv4 DHCP
client port (68) would not be available. This problem could be
resolved using one of the following two methods:
o The DHCPv4oSW client is updated to source BOOTP/DHCP requests
using a port taken from the client's allocated range. Likewise,
the DHCPv4oSW server must use the L4 source port from a client's
message as the destination port for the response.
o The DHCP Server Identifier Override Suboption described in
[RFC5107] could be used to direct all DHCPv4 messages through the
DHCPv4 relay. As option 82 is being used to identify the
destination IPv6 address for messages from the DHCPv4 server to
the client, the L4 destination port is not necessary for the
lookup process and could be left unchanged.
The protocol stack used for obtaining DHCPv4 based configuration is:
DHCPv4/UDPv4/IPv4/IPv6
1.6. DHCPv4oDHCPv6 Based Provisioning - Functional Overview
[I-D.ietf-dhc-dhcpv4-over-dhcpv6] describes transporting DHCPv4
messages within two new DHCPv6 messages types: BOOTREQUESTV6 and
BOOTREPLYV6. These new messages types must be implemented in both
the DHCPv4oDHCPv6 client and server.
In this approach, the configuration of stateless IPv4 addresses and
source ports (if required) is carried out using DHCPv6 as described
in section 1.3 above. Dynamic IPv4 addressing, and/or any additional
IPv4 configuration, is provided using DHCPv4 messages carried
(without IPv4/UDPv4 headers) within a new OPTION_BOOTP_MSG DHCPv6
option.
OPTION_BOOTP_MSG enables the client and server to send BOOTP/DHCPv4
messages verbatim across the IPv6 network. When a DHCPv4oDHCPv6
server receives a DHCPv6 request containing OPTION_BOOT_MSG within a
BOOTREQUESTV6 message, it passes it to the DHCPv4 server engine.
Likewise, the DHCPv4 server place its DHCPv4 response in the payload
of OPTION_BOOTP_MSG and puts this into a BOOTPRPLYV6 message.
DHCPv4 messages can be carried within DHCPv6 multicast messages,
using the All_DHCP_Relay_Agents_and_Servers multicast address. These
can be relayed in exactly the same way as any other DHCPv6
multicasted messages.
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Optionally, DHCPv6 relays could be updated so that they forward the
BOOTREQUESTV6 message to a different destination address, allowing
for the separation of DHCPv4 and DHCPv6 provisioning infrastructure.
If the DHCPv4oDHCPv6 client is provision with a unicast IPv6
address(es) for the server(s), then an entirely unicast message flow
between the client and server is also possible without the need for
relaying.
The protocol stack used for obtaining dynamic v4 addressing or
additional IPv4 configuration is as follows:
DHCPv4/DHCPv6/UDPv6/IPv6
2. Requirements for the Solution Evaluation
The following requirements have been defined to evaluate the
different approaches:
1. Minimize the amount of work necessary to implement the solution
through re-use of existing standards and implementations as much
as possible.
2. Provide a method of supporting all DHCPv4 options so that they
can be utilized without the need for further standardization.
3. Allow for the dynamic leasing of IPv4 addresses to clients. This
allows for more efficient use of limited IPv4 resources.
4. Enable the separation of IPv4 and IPv6 host configuration
infrastructure, i.e. independent DHCPv4 and DHCPv6 server
functions to restrict provisioning domains to the relevant
protocol and allow the removal of IPv4 infrastructure in the
future.
5. Avoid leaving legacy IPv4 options in DHCPv6.
6. Provide a flexible architecture to give operators the option of
only deploying the functional elements necessary for their
specific requirements.
7. Not restricted to specific IPv4 over IPv6 transport mechanisms or
architectures.
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3. Comparison of the Five Approaches
The table below provides a comparative evaluation showing how the
different approaches meet the solution requirements described above.
+-------+----------+--------+-----------+-----------+---------------+
| Req. | DHCPv4o6 | DHCPv6 | DHCPv6 + | DHCPv4oSW | DHCPv4oDHCPv6 |
| No. | | | Stateless | | |
| | | | DHCPv4oSW | | |
+-------+----------+--------+-----------+-----------+---------------+
| 1 | No | Yes | No | Yes | Yes |
| 2 | Yes | No | Yes | Yes | Yes |
| 3 | Yes | No | No | Yes | Yes |
| 4 | Yes | No | Yes | Yes | Yes |
| 5 | Yes | No | Yes | Yes | Yes |
| 6 | No | No | Yes | Yes | Yes |
| 7 | Yes | Yes | No | No | Yes |
+-------+----------+--------+-----------+-----------+---------------+
Table 1: Approach Comparison
The following sections of the document provide more detail on the
pros and cons of each of the approaches.
3.1. DHCPv4o6 Based Provisioning
3.1.1. Pros
1. Implementation makes all existing DHCPv4 options available with
no further ongoing development work necessary.
2. IPv4 and IPv6 based provisioning can be separated from each other
if required, allowing flexibility in network design.
3. Easy to implement through minor adaptation of existing DHCPv4
client, relay and server code.
4. No additional functional elements are necessary except the
DHCPv4o6 client relay agent and server. If a TSV is used, then a
TRA is not required.
5. Suitable for dynamic IPv4 address leases where the IPv4 address
lifetime is not linked to the lifetime of a DHCPv6 lease.
6. Implementations already exist, proving that the approach works.
3.1.2. Cons
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1. More new functional elements required within the architecture
(CRA, DHCPv4o6 server and optionally TRA) than are necessary in
DHCPv6 based provisioning.
2. A new DHCPv6 option is necessary in order to provision the IPv6
address of the DHCPv4 server to the end device.
3. The DHCPv4 client host needs to be updated to implement the IPv6
encapsulation and decapsulation function (i.e. An HCRA).
Otherwise a separate On-Link CRA (LCRA) functional element must
be deployed.
4. A DHCPv4 server must be deployed and maintained.
5. The DHCPv4 server needs to be updated to implement new DHCPv4o6
functionality.
3.2. DHCPv6 Based Provisioning
3.2.1. Pros
1. No additional functional elements are required except the DHCPv6
client and server.
2. A single protocol is used to deliver configuration information
for IPv4 and IPv6.
3. Single provisioning point for all configuration parameters.
4. Implementations already exist, proving that the approach works.
3.2.2. Cons
1. Any required DHCPv4 options must be ported to DHCPv6, which will
require re-development work for each option.
2. Means that DHCPv4 'legacy' options (which will be of decreasing
relevance in the future) will remain in DHCPv6 for the lifetime
of the protocol.
3. Each time that a DHCPv4 option is ported to DHCPv6, all clients
and servers and possibly relays would need to be updated to
implement the new option.
4. Architecture does not allow for the separation of IPv4 and IPv6
domains.
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5. Does not provide a mechanism for dynamic IPv4 address leasing,
where the lifetime of IPv4 addresses is not linked to the
lifetime of a DHCPv6 lease. A DHCPv4 lease lifetime management
mechanism would need to be added to DHCPv6 to implement this.
3.3. DHCPv6 + Stateless DHCPv4oSW Based Provisioning
3.3.1. Pros
1. Once implemented, all existing DHCPv4 options will be available
with no ongoing development work necessary.
2. Uses existing DHCPv4 and DHCPv6 architectures in order to provide
IPv4 configuration in an IPv6 only environment.
3. DHCPv4 and DHCPv6 based provisioning can be separated from each
other if required, allowing flexibility in network design.
3.3.2. Cons
1. More new functional elements required than are necessary in
DHCPv6 based provisioning.
2. IPv4 over IPv6 softwire approaches that distribute NAT to the CPE
and allow for IP address sharing (MAP-E & LW4o6) forbid the use
of reserved TCP/UDP ports (e.g. 0-1024). Every DHCPv4 client
sharing the same address needs to have a UDP listener running on
UDP port 68. To resolve this would require significant rework to
either the softwire mechanisms and/or the DHCPv4 client
implementation.
3. From the current specification, DHCPINFORM is not suitable for
use over a softwire. Additional work, such as the development of
'shims' would be necessary.
4. The current DHCPINFORM specification has a number of unclear
points, such as those described in
[I-D.ietf-dhc-dhcpinform-clarify]. Substantial work would be
required to resolve this.
5. Links the deployment of IPv4 configuration over IPv6 to a
softwire implementation (e.g. requiring a softwire concentrator
to act as a DHCPv4 relay). Whilst softwires are the only
application for this functionality at the moment, this may not be
the case in the future, meaning another solution may be required.
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6. A new mechanism must be defined in order to provide the DHCPv4
client with the IPv4 address of the DHCPv4 server so that unicast
DHCPINFORM messages can be sent.
7. As only the DHCPINFORM/DHCPACK DHCPv4 message types are
supported, dynamic IPv4 address leasing (using DHCPDISCOVER
messages) can not be used.
8. Restricted to underlying hub-and-spoke IPv4 over IPv6
architectures. The 'hub' is necessary for the location of the
DHCPv4 relay, as all traffic must pass through it. An underlying
mesh architecture does not have such a location to deploy the
relay function.
9. The approach is unproven as no existing implementations exist.
3.4. DHCPv4oSW Based Provisioning
3.4.1. Pros
1. Once implemented, all existing DHCPv4 options will be available
with no ongoing development work necessary.
2. Uses existing DHCPv4 architecture in order to provide IPv4
configuration in an IPv6 only environment.
3. DHCPv4 and DHCPv6 based provisioning can be separated from each
other if required, allowing flexibility in network design.
3.4.2. Cons
1. Requires the DHCPv4 client, DHCPv4 server and softwire
concentrator (or other relaying device) to be modified.
2. May require the DHCPv4 client and server to be updated to use
dynamic ports taken from the restricted port set allocated to the
client instead of the well-known DHCPv4 ports.
3. The DHCPv4 client must be modified to identify the properties of
the interface it is configuring and request parameters
accordingly (e.g. restricted port-sets cannot be used on Ethernet
transport interfaces but are allowed for a softwire transport)
4. Restricted to underlying hub-and-spoke IPv4 over IPv6
architectures. The 'hub' is necessary for the location of the
DHCPv4 relay, as all traffic, including DHCPDISCOVER messages
will pass through it. An underlying mesh architecture does not
have such a location to deploy the relay.
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3.5. DHCPv4oDHCPv6 Based Provisioning
3.5.1. Pros
1. Once implemented, all existing DHCPv4 options will be available
with no ongoing development work necessary.
2. Uses existing DHCPv4 and DHCPv6 architectures in order to provide
IPv4 configuration in an IPv6 only environment.
3. DHCPv4 and DHCPv6 based provisioning can be separated from each
other if required, allowing flexibility in network design.
4. Suitable for the provisioning of dynamic IPv4 configuration as
the existing DHCPv4 leasing mechanism can be used.
3.5.2. Cons
1. More new functional elements within the architecture than are
necessary in DHCPv6 based provisioning.
2. DHCPv6 clients needs to be updated to implement the new DHCPv6
message types (BOOTPREQUESTv6 and BOOTPREPLYv6).
3. The DHCPv6 server needs to be updated to implement new
DHCPv4oDHCPv6 message types and functionality.
4. The approach is currently unproven as no existing implementations
exist.
4. Conclusion
Whilst all of the approaches described here will require some
development work to realize, it is clear from the above analysis that
the most sustainable approach capitalizes on existing DHCPv4
implementations and include them as new DHCPv6 message types. The
main rationale for this is that it enables all of DHCPv4's existing
options to be migrated for use over IPv6 in a single step.
Porting of all necessary DHCPv4 options to DHCPv6 would require
ongoing development work, re-implementing existing DHCPv4
functionality in DHCPv6. This will result in having legacy DHCPv4
options in DHCPv6, which will no longer be useful once IPv4 is
completely abandoned.
Therefore, the DHCPv6 approach is not suitable for delivering IPv4
configuration parameters in an efficient, ongoing manner.
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The dynamic leasing of IPv4 addresses is fundamental to the efficient
use of remaining IPv4 resources. This will become increasingly
important in the future, so a mechanism which supports this is
necessary. DHCPv6 + Stateless DHCPv4oSW does not provide this
function and so is not recommended.
The DHCPv4o6 approach requires a DHCPv4 server (with DHCPv4o6
functionality) for all deployment scenarios, even when DHCPv4
specific functionality (e.g. sending DHCPv4 options) is not required
by the operator.
DHCPv4o6 requires that there is a tunnel concentrator, or similar
'hub' in the underlying architecture so that a DHCP relay can be
deployed. This does not meet Requirement 7.
Therefore, this memo recommends DHCPv4oDHCPv6
[I-D.ietf-dhc-dhcpv4-over-dhcpv6] as the best underlying approach for
provisioning IPv4 parameters over an IPv6 only network.
5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
The following sections provide pointers to the documented security
considerations associated with each approach.
6.1. DHCPv4oIPv6
Security considerations associated with this approach are described
in Section 8 of [I-D.ietf-dhc-dhcpv4-over-ipv6].
6.2. DHCPv6
Security considerations associated with this approach are described
in Section 23 of [RFC3315].
6.3. DHCPv6+DHCPv4oSW
There is currently no document describing this mechanism, so no
security considerations have been documented.
6.4. DHCPv4oSW
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At the time of writing, [I-D.troan-dhc-dhcpv4osw] does not list any
security considerations.
6.5. DHCPv4oDHCPv6
Security considerations associated with this approach are described
in Section 10 of [RFC3315].
7. Acknowledgements
Thanks to Ted Lemon, Tomek Mrugalski, Ole Troan and Francis Dupont
for their input and reviews.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[I-D.ietf-dhc-dhcpinform-clarify]
Hankins, D., "Dynamic Host Configuration Protocol
DHCPINFORM Message Clarifications", draft-ietf-dhc-
dhcpinform-clarify-06 (work in progress), October 2011.
[I-D.ietf-dhc-dhcpv4-over-dhcpv6]
Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4 over DHCPv6 Transport", draft-ietf-dhc-
dhcpv4-over-dhcpv6-02 (work in progress), October 2013.
[I-D.ietf-dhc-dhcpv4-over-ipv6]
Cui, Y., Wu, P., Wu, J., Lemon, T., and Q. Sun, "DHCPv4
over IPv6 Transport", draft-ietf-dhc-dhcpv4-over-ipv6-08
(work in progress), October 2013.
[I-D.ietf-softwire-lw4over6]
Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and
I. Farrer, "Lightweight 4over6: An Extension to the DS-
Lite Architecture", draft-ietf-softwire-lw4over6-03 (work
in progress), November 2013.
[I-D.ietf-softwire-map-dhcp]
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Mrugalski, T., Troan, O., Dec, W., Bao, C.,
leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options
for configuration of Softwire Address and Port Mapped
Clients", draft-ietf-softwire-map-dhcp-06 (work in
progress), November 2013.
[I-D.ietf-softwire-map-t]
Li, X., Bao, C., Dec, W., Troan, O., Matsushima, S., and
T. Murakami, "Mapping of Address and Port using
Translation (MAP-T)", draft-ietf-softwire-map-t-04 (work
in progress), September 2013.
[I-D.ietf-softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, "Mapping of Address and Port
with Encapsulation (MAP)", draft-ietf-softwire-map-08
(work in progress), August 2013.
[I-D.mrugalski-softwire-dhcpv4-over-v6-option]
Mrugalski, T. and P. Wu, "Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) Option for DHCPv4 over IPv6
Endpoint", draft-mrugalski-softwire-
dhcpv4-over-v6-option-01 (work in progress), September
2012.
[I-D.troan-dhc-dhcpv4osw]
Troan, O., "DHCPv4 over A+P softwires", draft-troan-dhc-
dhcpv4osw-00 (work in progress), June 2013.
[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.
[RFC5107] Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,
"DHCP Server Identifier Override Suboption", RFC 5107,
February 2008.
Authors' Addresses
Branimir Rajtar
Hrvatski Telekom
Zagreb
Croatia
Email: branimir.rajtar@t.ht.hr
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Ian Farrer
Deutsche Telekom AG
Bonn
Germany
Email: ian.farrer@telekom.de
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