Internet DRAFT - draft-ietf-dhc-dhcpv4-over-dhcpv6
draft-ietf-dhc-dhcpv4-over-dhcpv6
DHC Working Group Q. Sun
Internet-Draft Y. Cui
Intended status: Standards Track Tsinghua University
Expires: December 13, 2014 M. Siodelski
ISC
S. Krishnan
Ericsson
I. Farrer
Deutsche Telekom AG
June 11, 2014
DHCPv4 over DHCPv6 Transport
draft-ietf-dhc-dhcpv4-over-dhcpv6-09
Abstract
IPv4 connectivity is still needed as networks migrate towards IPv6.
Users require IPv4 configuration even if the uplink to their service
provider supports IPv6 only. This document describes a mechanism for
obtaining IPv4 configuration information dynamically in IPv6 networks
by carrying DHCPv4 messages over DHCPv6 transport. Two new DHCPv6
messages and two new DHCPv6 options are defined for this purpose.
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
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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 December 13, 2014.
Copyright Notice
Copyright (c) 2014 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Architecture Overview . . . . . . . . . . . . . . . . . . . . 4
6. New DHCPv6 Messages . . . . . . . . . . . . . . . . . . . . . 5
6.1. Message Types . . . . . . . . . . . . . . . . . . . . . . 6
6.2. Message Formats . . . . . . . . . . . . . . . . . . . . . 6
6.3. DHCPv4-query Message Flags . . . . . . . . . . . . . . . 7
6.4. DHCPv4-response Message Flags . . . . . . . . . . . . . . 7
7. New DHCPv6 Options . . . . . . . . . . . . . . . . . . . . . 7
7.1. DHCPv4 Message Option Format . . . . . . . . . . . . . . 7
7.2. 4o6 Server Address Option Format . . . . . . . . . . . . 8
8. Use of the DHCPv4-query Unicast Flag . . . . . . . . . . . . 9
9. DHCP 4o6 Client Behavior . . . . . . . . . . . . . . . . . . 10
10. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . 12
11. DHCP 4o6 Server Behavior . . . . . . . . . . . . . . . . . . 12
12. Security Considerations . . . . . . . . . . . . . . . . . . . 13
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
14. Contributors List . . . . . . . . . . . . . . . . . . . . . . 14
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
15.1. Normative References . . . . . . . . . . . . . . . . . . 14
15.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
As the migration towards IPv6 continues, IPv6-only networks will
become more prevalent. In such networks, IPv4 connectivity will
continue to be provided as a service over IPv6-only networks. In
addition to provisioning IPv4 addresses for clients of this service,
other IPv4 configuration parameters may also be needed (e.g.
addresses of IPv4-only services).
This document describes a transport mechanism to carry DHCPv4
messages using the DHCPv6 protocol for the dynamic provisioning of
IPv4 addresses and other DHCPv4 specific configuration parameters
across IPv6-only networks. It leverages the existing DHCPv4
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infrastructure, e.g. failover, DNS updates, DHCP Leasequery, etc.
When IPv6 multicast is used to transport 4o6 messages, another
benefit is that the operator can gain information about the
underlying IPv6 network the 4o6 client is connected to from the the
DHCPv6 relay agents the request has passed through.
2. 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 [RFC2119].
3. Terminology
This document makes use of the following terms:
CPE: Customer Premises Equipment (also
known as Customer Provided
Equipment), which provides access for
devices connected to a Local Area
Network (typically at the customer's
site/home) to the Internet Service
Provider's network.
DHCP 4o6 client (or client): A DHCP client supporting both the
DHCPv6 protocol [RFC3315] as well as
the DHCPv4 over DHCPv6 protocol
described in this document. Such a
client is capable of requesting IPv6
configuration using DHCPv6 and IPv4
configuration using DHCPv4 over
DHCPv6.
DHCP 4o6 server (or server): A DHCP server that is capable of
processing DHCPv4 packets
encapsulated in the DHCPv4 Message
option (defined below).
DHCPv4 over DHCPv6: A protocol described in this
document, used to carry DHCPv4
messages in the payload of DHCPv6
messages.
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4. Applicability
The mechanism described in this document is not universally
applicable. This is intended as a special-purpose mechanism that
will be implemented on nodes that must obtain IPv4 configuration
information using DHCPv4 in specific environments where native DHCPv4
is not available. Such nodes are expected to follow the advice in
the "client behavior" section; nodes that do not require this
functionality are expected not to implement it, or not to enable it
by default. This mechanism may be enabled using an administrative
control, or may be enabled automatically in accordance with the needs
of some dual-stack transition mechanism such as
[I-D.ietf-softwire-lw4over6]. Such mechanisms are beyond the scope
of this document.
5. Architecture Overview
The architecture described here addresses a typical use case, where a
DHCP client's uplink supports IPv6 only and the Service Provider's
network supports IPv6 and limited IPv4 services. In this scenario,
the client can only use the IPv6 network to access IPv4 services, so
IPv4 services must be configured using IPv6 as the underlying network
protocol.
Although the purpose of this document is to address the problem of
communication between the DHCPv4 client and the DHCPv4 server, the
mechanism that it describes does not restrict the transported
messages types to DHCPv4 only. As the DHCPv4 message is a special
type of BOOTP message, BOOTP messages [RFC0951] MAY also be
transported using the same mechanism.
DHCP clients may be running on CPE devices, end hosts or any other
device that supports the DHCP client function. This document uses
the CPE as an example for describing the mechanism. This does not
preclude any end-host, or other device requiring IPv4 configuration,
from implementing DHCPv4 over DHCPv6 in the future.
This mechanism works by carrying DHCPv4 messages encapsulated within
the newly defined DHCPv6 messages. The DHCPv6 relay encapsulation is
used solely to deliver DHCPv4 packets to a DHCPv4-capable server, and
do not allocate any IPv6 addresses nor provide IPv6 configuration
information to the client. Figure 1, below, illustrates one possible
deployment architecture of this mechanism.
The DHCP 4o6 client implements a new DHCPv6 message called
DHCPv4-query, which contains a new option called the DHCPv4 Message
option encapsulating a DHCPv4 message sent by the client. The format
of this option is described in Section 7.1.
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The DHCPv6 message can be transmitted either via DHCPv6 Relay Agents
or directly to the DHCP 4o6 server. The server replies with a
DHCPv4-response message, which is a new DHCPv6 message carrying the
DHCPv4 response encapsulated in the DHCPv4 Message option.
_____________ _____________
/ \ / \
| | | |
+--------+-+ IPv6 +-+-----------+-+ IPv6 +-+--------+
| DHCP 4o6 | network | DHCPv6 | network | DHCP 4o6 |
| client +---------+ Relay Agent +---------+ Server |
| (on CPE) | | | | |
+--------+-+ +-+-----------+-+ +-+--------+
| | | |
\_____________/ \_____________/
Figure 1: Architecture Overview
Before the client can use DHCPv4 over DHCPv6, it MUST obtain the
necessary IPv6 configuration. The client requests the 4o6 Server
Address option from the server by sending the option code in Option
Request option as described in [RFC3315]. If the server responds
with the 4o6 Server Address option, it is an indication to the client
to attempt using DHCPv4 over DHCPv6 to obtain IPv4 configuration.
Otherwise, the client MUST NOT use DHCPv4 over DHCPv6 to request IPv4
configuration.
The client obtains the address(es) of the DHCP 4o6 server(s) from the
4o6 Server Address option and uses them to communicate with the DHCP
4o6 servers as described in Section 9. If the 4o6 Server Address
option contains no addresses (is empty), the client uses the well-
known All_DHCP_Relay_Agents_and_Servers multicast address to
communicate with the DHCP 4o6 server(s).
Before applying for an IPv4 address via a DHCPv4-query message, the
client must identify a suitable network interface for the address.
Once the request is acknowledged by the server, the client can
configure the address and other relevant parameters on this
interface. The mechanism for determining a suitable interface is out
of the scope of the document.
6. New DHCPv6 Messages
Two new DHCPv6 messages carry DHCPv4 messages between the client and
the server using the DHCPv6 protocol: DHCPv4-query and
DHCPv4-response. This section describes the structures of these
messages.
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6.1. Message Types
DHCPV4-QUERY (TBD): The DHCP 4o6 client sends a DHCPv4-query
message to a DHCP 4o6 server. The DHCPv4
Message option carried by this message
contains a DHCPv4 message that the DHCP 4o6
client uses to request IPv4 configuration
parameters from the server.
DHCPv4-RESPONSE (TBD): A DHCP 4o6 server sends a DHCPv4-response
message to a DHCP 4o6 client. It contains a
DHCPv4 Message option carrying a DHCPv4
message in response to a DHCPv4 message
received by the server in the DHCPv4 Message
option of the DHCPv4-query message.
6.2. Message Formats
Both DHCPv6 messages defined in this document share the following
format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. options .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The format of DHCPv4-query and DHCPv4-response messages
msg-type Identifies the message type. It can be either
DHCPV4-QUERY (TBD) or DHCPV4-RESPONSE (TBD)
corresponding to the contained DHCPv4-query or
DHCPv4-response, respectively.
flags Specifies flags providing additional information
required by the server to process the DHCPv4 message
encapsulated in the DHCPv4-query message, or required
by the client to process a DHCPv4 message
encapsulated in the DHCPv4-response message.
options Options carried by the message. The DHCPv4 Message
Option (described in Section 7.1) MUST be carried by
the message. Only DHCPv6 options for IPv4
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configuration may be included in this field. It MUST
NOT contain DHCPv6 options related solely to IPv6, or
IPv6-only service configuration.
6.3. DHCPv4-query Message Flags
The "flags" field of the DHCPv4-query is used to carry additional
information that may be used by the server to process the
encapsulated DHCPv4 message. Currently only one bit of this field is
used. Remaining bits are reserved for the future use. The "flags"
field has the following format:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: DHCPv4-query flags format
U Unicast Flag. If set to 1, it indicates that the
DHCPv4 message encapsulated within the DHCPv4-query
message would be sent to a unicast address if it was
sent using IPv4. If this flag is set to 0, it
indicates that the DHCPv4 message would be sent to
the broadcast address if it was sent using IPv4. The
usage of the flag is described in detail in
Section 8.
MBZ Bits MUST be set to zero when sending and MUST be
ignored when receiving.
6.4. DHCPv4-response Message Flags
This document introduces no flags to be carried in the "flags" field
of the DHCPv4-response message. They are all reserved for the future
use. The DHCP 4o6 server MUST set all bits of this field to 0 and
the DHCP 4o6 client MUST ignore the content in this field.
7. New DHCPv6 Options
7.1. DHCPv4 Message Option Format
The DHCPv4 Message option carries a DHCPv4 message that is sent by
the client or the server. Such messages exclude any IP or UDP
headers.
The format of the DHCPv4 Message option is:
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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-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. DHCPv4-message .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: DHCPv4 Message option Format
option-code OPTION_DHCPV4_MSG (TBD).
option-len Length of the DHCPv4 message.
DHCPv4-message The DHCPv4 message sent by the client or the server.
In a DHCPv4-query message it contains a DHCPv4
message sent by a client. In a DHCPv4-response
message it contains a DHCPv4 message sent by a server
in response to a client.
7.2. 4o6 Server Address Option Format
The 4o6 Server Address option is sent by a server to a client
requesting IPv6 configuration using DHCPv6 [RFC3315]. It carries a
list of DHCP 4o6 servers' IPv6 addresses that the client should
contact to obtain IPv4 configuration. This list may include
multicast and unicast addresses. The client sends its requests to
all unique addresses carried in this option.
This option may also carry no IPv6 addresses, which instructs the
client to use the All_DHCP_Relay_Agents_and_Servers multicast address
as the destination address.
The presence of this option in the server's response indicates to the
client that it should use DHCPv4 over DHCPv6 to obtain IPv4
configuration. If the option is absent, the client MUST NOT enable
DHCPv4-over-DHCPv6 function.
The format of the 4o6 Server Address option is:
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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-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. IPv6 Address(es) .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: 4o6 Servers Address Option Format
option-code OPTION_DHCP4_O_DHCP6_SERVER (TBD).
option-len Length of the IPv6 address(es) carried by the option,
i.e. multiple of 16 octets. Minimal length of this
option is 0.
IPv6 Address Zero or more IPv6 addresses of the DHCP 4o6
Server(s).
8. Use of the DHCPv4-query Unicast Flag
A DHCPv4 client conforming to [RFC2131] may send its DHCPREQUEST
message to either a broadcast or unicast address depending on its
state. For example, a client in the RENEWING state uses a unicast
address to contact the DHCPv4 server to renew its lease. A client in
the REBINDING state uses a broadcast address.
In DHCPv4 over DHCPv6, IPv6 is used to deliver DHCPv4 messages to the
DHCP 4o6 server. There is no relation between the outer IPv6 address
and the inner DHCPv4 message. As a result, the server is unable to
determine whether the received DHCPv4 messages should have been sent
using broadcast or unicast in IPv4 by checking the IPv6 address.
In order to allow the server to determine the client's state, the
"Unicast" flag is carried in the DHCPv4-query message. The client
MUST set this flag to 1 when the DHCPv4 message would have been sent
to the unicast address if using DHCPv4 over IPv4. This flag MUST be
set to 0 if the DHCPv4 client would have sent the message to the
broadcast address in IPv4. The choice whether a given message should
be sent to a broadcast or unicast address is made based on the
[RFC2131] and its extensions.
Note: The "Unicast" flag reflects how the DHCPv4 packet would have
been sent; not how the DHCPv6 packet itself is sent.
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9. DHCP 4o6 Client Behavior
The client MUST obtain necessary IPv6 configuration from a DHCPv6
server before using DHCPv4 over DHCPv6. The client requests the 4o6
Server Address option using Option Request option (ORO) in every
Solicit, Request, Renew, Rebind and Information-request message. If
the DHCPv6 server includes the 4o6 Server Address option in its
response, it is an indication that the client can use DHCPv4 over
DHCPv6 to obtain the IPv4 configuration (by sending DHCPv4 messages
encapsulated in DHCPv4-query messages).
The client MUST NOT use DHCPv4 over DHCPv6 to request IPv4
configuration if the DHCPv6 server does not include the 4o6 Server
Address option. If the IPv6 configuration that contained the 4o6
Server Address option subsequently expires, or if the renewed IPv6
configuration does not contain the 4o6 Server Address option, the
client MUST stop using DHCPv4 over DHCPv6 to request or renew IPv4
configuration. However, the client continues to request 4o6 Server
Address option in the messages sent to the DHCPv6 server as long as
it desires to use DHCPv4 over DHCPv6.
It is possible in a multi-homed configuration for there to be more
than one DHCPv6 configuration active at the same time that contains a
4o6 Server Address option. In this case, the configurations are
treated as being independent, so that when any such configuration is
active, a DHCPv4-over-DHCPv6 function may be enabled for that
configuration.
An implementation may also treat such configurations as being
exclusive, such that only one is kept active at a time. In this
case, the client keeps the same configuration active continuously as
long as it is valid. If that configuration becomes invalid but one
or more other configurations remain valid, the client activates one
of the remaining valid configurations.
Which strategy to follow is dependent on the implementation: keeping
multiple configurations active at the same time may provide useful
redundancy in some applications, but may be needlessly complex in
other cases.
If the client receives the 4o6 Server Address option and DHCPv4
[RFC2131] is used on the interface over which the DHCPv6 option was
received, the client MUST stop using the IPv4 configuration received
using DHCPv4 on this interface. The client MAY send a DHCPRELEASE to
the DHCPv4 server to relinquish an existing lease as described in
[RFC2131] in section 4.4.6. The client MUST NOT use DHCPv4 on this
interface as long as it receives 4o6 Server Address option in the
messages received from the DHCPv6 server.
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If the client receives a 4o6 Server Address option that contains no
IP addresses, i.e. the option is empty, the client MUST send its
requests to the All_DHCP_Relay_Agents_and_Servers multicast address.
If there is a list of IP addresses in the option, the client SHOULD
send requests to each unique address carried by the option.
If the client obtained stateless IPv6 configuration by sending
Information-request message to the server, the client MUST follow the
rules in [RFC4242] to periodically refresh the DHCPv4-over-DHCPv6
configuration (i.e. list of DHCP 4o6 servers) as well as other
configuration data. The client which obtained stateful IPv6
configuration will refresh the status of DHCPv4-over-DHCPv6 function
when extending a lifetime of acquired IPv6 address (Renew and Rebind
messages).
The client MUST employ an IPv6 address of an appropriate scope to
source the DHCPv4-query message from. When the client sends a
DHCPv4-query message to the multicast address, it MUST use a link-
local address as the source address as described in [RFC3315]. When
the client sends a DHCPv4-query message using unicast, the source
address MUST be an address of appropriate scope, acquired in advance.
The client generates a DHCPv4 message and stores it verbatim in the
DHCPv4 Message option carried by the DHCPv4-query message. The
client MUST put exactly one DHCPv4 Message option into a single
DHCPv4-query message. The client MUST NOT request the 4o6 Server
Address option in the DHCPv4-query message.
The client MUST follow rules defined in Section 8 when setting the
Unicast flag based on the DHCPv4 destination.
On receiving a DHCPv4-response message, the client MUST look for the
DHCPv4 Message option within this message. If this option is not
found, the DHCPv4-response message is discarded. If the DHCPv4
Message option is present, the client extracts the DHCPv4 message it
contains and processes it as described in section 4.4 of [RFC2131].
When dealing with IPv4 configuration, the client MUST follow the
normal DHCPv4 retransmission requirements and strategy as specified
in section 4.1 of [RFC2131]. There are no explicit transmission
parameters associated with a DHCPv4-query message, as this is
governed by the DHCPv4 [RFC2131] "state machine".
The client MUST implement [RFC4361] to ensure that the device
correctly identifies itself. It MUST send a 'client identifier'
option when using DHCPv4 over DHCPv6.
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10. Relay Agent Behavior
When a DHCPv6 relay agent receives a DHCPv4-query message, it may not
recognize this message. The unknown message MUST be forwarded as
described in [I-D.ietf-dhc-dhcpv6-unknown-msg].
If it recognises the message, the DHCPv6 relay agent MAY allow the
configuration of a dedicated DHCPv4 over DHCPv6 specific destination
address(es), differing from the address(es) of the DHCPv6-only
server(s). To implement this function, the relay checks the received
DHCPv6 message type and forwards according to the following logic:
1. If the message type is DHCPV4-QUERY, the packet is relayed to the
configured DHCP 4o6 Server's address(es) in the form of normal
DHCPv6 packet (i.e. DHCPv6/UDP/IPv6).
2. For any other DHCPv6 message type, forward according to section
20 of [RFC3315].
The above logic only allows for separate relay destinations
configured on the relay agent closest to the client (single relay
hop). Multiple relaying hops are not considered in the case of
separate relay destinations.
11. DHCP 4o6 Server Behavior
When the server receives a DHCPv4-query message from a client, it
searches for the DHCPv4 Message option. The server discards a packet
without this option. In addition, the server MAY notify an
administrator about the receipt of this malformed packet. The
mechanism for this notification is out of scope for this document.
If the server finds a valid DHCPv4 Message option, it extracts the
original DHCPv4 message. Since the DHCPv4 message is encapsulated in
the DHCPv6 message, it lacks the information which is typically used
by the DHCPv4 server, implementing [RFC2131], to make address
allocation decisions, e.g. giaddr for relayed messages and IPv4
address of the interface which the server is using to communicate
with directly connected client. Therefore, the DHCP 4o6 server
allocates addresses according to the local address assignment
policies determined by the server administrator. For example, if the
DHCPv4-query message has been sent via a relay, the server MAY use
the link-address field of the Relay-forward message as a lookup for
the IPv4 subnet to assign DHCPv4 address from. If the DHCPv4-query
message has been sent from a directly connected client, the server
MAY use IPv6 source address of the message to determine the
appropriate IPv4 subnet to use for DHCPv4 address assignment.
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Alternatively, the server may act as a DHCPv4 relay agent and forward
the DHCPv4 packet to a "normal" DHCPv4 server. The details of such a
solution have not been considered by the working group; describing
that solution is out of scope of this document and is left as future
work should the need for it arise.
The server SHOULD use the "flags" field of the DHCPv4-query message
to create a response (server to client DHCPv4 message). The use of
this field is described in detail in Section 8.
When an appropriate DHCPv4 response is created, the server places it
in the payload of a DHCPv4 Message option, which it puts into the
DHCPv4-response message.
If the DHCPv4-query message was received directly by the server, the
DHCPv4-response message MUST be unicast from the interface on which
the original message was received.
If the DHCPv4-query message was received in a Relay-forward message,
the server creates a Relay-reply message with the DHCPv4-response
message in the payload of a Relay Message option, and responds as
described in section 20.3 of [RFC3315].
12. Security Considerations
In this specification, DHCPv4 messages are encapsulated in the newly
defined option and messages. This is similar to the handling of the
current relay agent messages. In order to bypass firewalls or
network authentication gateways, a malicious attacker may leverage
this feature to convey other messages using DHCPv6, i.e. use DHCPv6
as a form of encapsulation. However, the potential risk from this is
no more severe than that with the current DHCPv4 and DHCPv6 practice.
It is possible for a rogue server to reply with a 4o6 Server Address
Option containing duplicated IPv6 addresses, which could cause an
amplification attack. To avoid this, the client MUST check if there
are duplicate IPv6 addresses in a 4o6 Server Address Option when
receiving one. The client MUST ignore any but the first instance of
each address.
When considering whether to enable DHCPv4-over-DHCPv6, one important
consideration is that when it is enabled, this gives the DHCPv6
server the ability to shut off DHCPv4 traffic, and, consequently,
IPv4 traffic, on the interface that is configured to do DHCPv4-over-
DHCPv6. For this reason, DHCPv4-over-DHCPv6 should only be enabled
in situations where there is a clear trust relationship that
eliminates this concern. For instance, a CPE device can safely
enable this on its WAN interface, because it is reasonable to assume
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that an ISP will not accidentally configure DHCPv4 over DHCPv6
service on that link, and that it will be impractical for an attacker
to set up a rogue DHCPv6 server in the ISP's network.
13. IANA Considerations
IANA is requested to allocate two DHCPv6 option codes for use by
OPTION_DHCPV4_MSG and OPTION_DHCP4_O_DHCP6_SERVER from the "Option
Codes" table, and two DHCPv6 message type codes for the DHCPV4-QUERY
and DHCPV4-RESPONSE from the "Message Types" table of the Dynamic
Host Configuration Protocol for IPv6 (DHCPv6) Registry. Both tables
can be found at http://www.iana.org/assignments/dhcpv6-parameters/.
14. Contributors List
Many thanks to Ted Lemon, Bernie Volz, Tomek Mrugalski, Cong Liu and
Yuchi Chen, for their great contributions to the specification.
15. References
15.1. Normative References
[I-D.ietf-dhc-dhcpv6-unknown-msg]
Cui, Y., Sun, Q., and T. Lemon, "Handling Unknown DHCPv6
Messages", draft-ietf-dhc-dhcpv6-unknown-msg-08 (work in
progress), March 2014.
[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.
[RFC4242] Venaas, S., Chown, T., and B. Volz, "Information Refresh
Time Option for Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 4242, November 2005.
[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.
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15.2. Informative References
[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-lw4over6-10 (work
in progress), June 2014.
[RFC0951] Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
September 1985.
Authors' Addresses
Qi Sun
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5822
Email: sunqi@csnet1.cs.tsinghua.edu.cn
Yong Cui
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6260-3059
Email: yong@csnet1.cs.tsinghua.edu.cn
Marcin Siodelski
950 Charter Street
Redwood City, CA 94063
USA
Phone: +1 650 423 1431
Email: msiodelski@gmail.com
Suresh Krishnan
Ericsson
Email: suresh.krishnan@ericsson.com
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Ian Farrer
Deutsche Telekom AG
GTN-FM4,Landgrabenweg 151
Bonn, NRW 53227
Germany
Email: ian.farrer@telekom.de
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