Internet Engineering Task Force (IETF) D. Evans
Request for Comments: 6644 IPfonix, Inc.
Updates: 3315 R. Droms
Category: Standards Track Cisco Systems, Inc.
ISSN: 2070-1721 S. Jiang
Huawei Technologies Co., Ltd
July 2012
Rebind Capability in DHCPv6 Reconfigure Messages
Abstract
This document updates RFC 3315 (DHCPv6) to allow the Rebind message
type to appear in the Reconfigure Message option of a Reconfigure
message. It extends the Reconfigure message to allow a DHCPv6 server
to cause a DHCPv6 client to send a Rebind message. The document also
clarifies how a DHCPv6 client responds to a received Reconfigure
message.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 5741.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6644.
Evans, et al. Standards Track [Page 1]RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
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Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................3
3. The Reconfigure Message Option of the DHCPv6 Reconfigure
Message .........................................................3
4. Server Behavior .................................................4
5. Client Behavior .................................................7
6. Clarification of Section 19.4.2, RFC 3315 .......................8
7. Security Considerations .........................................8
8. Acknowledgements ................................................9
9. References ......................................................9
9.1. Normative References .......................................9
9.2. Informative References.....................................9
Evans, et al. Standards Track [Page 2]RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
1. Introduction
DHCPv6 [RFC3315] allows a server to send an unsolicited Reconfigure
message to a client. The client's response to a Reconfigure message,
according to Section 19 of RFC 3315, is either a Renew or an
Information-request message, depending on the contents of the
msg-type field in the Reconfigure Message option of the Reconfigure
message. If the client sends a Renew message, it includes a Server
Identifier option in the Renew message to specify the server that
should respond to the Renew message. The specification defined in
RFC 3315 is suitable only for scenarios in which the client would
communicate with the same DHCPv6 servers.
There are also scenarios where the client must communicate with a
different server; for example, a network administrator may choose to
shut down a DHCPv6 server and move the clients who most recently
communicated with it to a different server. Hence, this document
expands the allowed values of the message type field within the
reconfiguration message to allow the server to indicate to the client
to send a Rebind message, which does not include a Server Identifier
option, and allows any server to respond to the client.
RFC 3315 does not specify that a Reconfigure message must be sent
from the server with which the client most recently communicated, and
it does not specify which server the client should identify with a
Server Identifier option when the client responds to the Reconfigure
message. This document clarifies that the client should send a Renew
message in response to a Reconfigure message with a Server Identifier
option identifying the same server that the client would have
identified if the client had sent the Renew message after expiration
of the timer T1.
2. Terminology
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].
This document uses IPv6 and DHCPv6 terms as defined in Section 4 of
[RFC3315].
3. The Reconfigure Message Option of the DHCPv6 Reconfigure Message
This section modifies Section 22.19 of RFC 3315 to allow the
specification of the Rebind message in a Reconfigure message.
Evans, et al. Standards Track [Page 3]
RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
A server includes a Reconfigure Message option in a Reconfigure
message to indicate to the client whether the client responds with a
Renew, an Information-request, or a Rebind message.
The format of this 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_RECONF_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type |
+-+-+-+-+-+-+-+-+
option-code OPTION_RECONF_MSG (19).
option-len 1.
msg-type 5 for Renew message, 6 for Rebind, 11 for
Information-request message.
4. Server Behavior
This section updates specific text in Sections 19.1 and 19.2 of RFC
3315.
Section 19.1.1:
OLD:
The server MUST include a Reconfigure Message option (defined in
section 22.19) to select whether the client responds with a Renew
message or an Information-Request message.
The server MUST NOT include any other options in the Reconfigure
except as specifically allowed in the definition of individual
options.
A server sends each Reconfigure message to a single DHCP client,
using an IPv6 unicast address of sufficient scope belonging to the
DHCP client. If the server does not have an address to which it can
send the Reconfigure message directly to the client, the server uses
a Relay-reply message (as described in section 20.3) to send the
Reconfigure message to a relay agent that will relay the message to
the client. The server may obtain the address of the client (and the
appropriate relay agent, if required) through the information the
server has about clients that have been in contact with the server,
or through some external agent.
Evans, et al. Standards Track [Page 4]RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
To reconfigure more than one client, the server unicasts a separate
message to each client. The server may initiate the reconfiguration
of multiple clients concurrently; for example, a server may send a
Reconfigure message to additional clients while previous
reconfiguration message exchanges are still in progress.
The Reconfigure message causes the client to initiate a Renew/Reply
or Information-request/Reply message exchange with the server. The
server interprets the receipt of a Renew or Information-request
message (whichever was specified in the original Reconfigure message)
from the client as satisfying the Reconfigure message request.
NEW:
The server MUST include a Reconfigure Message option (as defined in
Section 3 of RFC 6644) to select whether the client responds with a
Renew message, a Rebind message, or an Information-request message.
The server MUST NOT include any other options in the Reconfigure,
except as specifically allowed in the definition of individual
options.
A server sends each Reconfigure message to a single DHCP client,
using an IPv6 unicast address of sufficient scope belonging to the
DHCP client. If the server does not have an address to which it can
send the Reconfigure message directly to the client, the server uses
a Relay-reply message (as described in Section 20.3) to send the
Reconfigure message to a relay agent that will relay the message to
the client. The server may obtain the address of the client (and the
appropriate relay agent, if required) through the information the
server has about clients that have been in contact with the server,
or through some external agent.
To reconfigure more than one client, the server unicasts a separate
message to each client. The server may initiate the reconfiguration
of multiple clients concurrently; for example, a server may send a
Reconfigure message to additional clients while previous
reconfiguration message exchanges are still in progress.
The Reconfigure message causes the client to initiate a Renew/Reply,
a Rebind/Reply message exchange, or an Information-request/Reply
message exchange. The server interprets the receipt of a Renew, a
Rebind, or an Information-request message (whichever was specified in
the original Reconfigure message) from the client as satisfying the
Reconfigure message request.
Evans, et al. Standards Track [Page 5]
RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
Section 19.1.2:
OLD:
If the server does not receive a Renew or Information-request message
from the client in REC_TIMEOUT milliseconds, the server retransmits
the Reconfigure message, doubles the REC_TIMEOUT value and waits
again. The server continues this process until REC_MAX_RC
unsuccessful attempts have been made, at which point the server
SHOULD abort the reconfigure process for that client.
NEW:
If the server does not receive a Renew, Rebind, or Information-
request message from the client in REC_TIMEOUT milliseconds, the
server retransmits the Reconfigure message, doubles the REC_TIMEOUT
value, and waits again. The server continues this process until
REC_MAX_RC unsuccessful attempts have been made, at which point the
server SHOULD abort the reconfigure process for that client.
Section 19.2:
OLD:
19.2. Receipt of Renew or Rebind Messages
The server generates and sends a Reply message to the client as
described in sections 18.2.3 and 18.2.8, including options for
configuration parameters.
The server MAY include options containing the IAs and new values for
other configuration parameters in the Reply message, even if those
IAs and parameters were not requested in the Renew message from the
client.
NEW:
19.2. Receipt of Renew Messages
In response to a Renew message, the server generates and sends a
Reply message to the client as described in Sections 18.2.3 and
18.2.8, including options for configuration parameters.
In response to a Rebind message, the server generates and sends a
Reply message to the client as described in Sections 18.2.4 and
18.2.8, including options for configuration parameters.
Evans, et al. Standards Track [Page 6]
RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
The server MAY include options containing the identity associations
(IAs) and new values for other configuration parameters in the Reply
message, even if those IAs and parameters were not requested in the
Renew or Rebind message from the client.
5. Client Behavior
This section updates specific text in Section 19.4 of RFC 3315.
Section 19.4.1:
OLD:
Upon receipt of a valid Reconfigure message, the client responds with
either a Renew message or an Information-request message as indicated
by the Reconfigure Message option (as defined in section 22.19). The
client ignores the transaction-id field in the received Reconfigure
message. While the transaction is in progress, the client silently
discards any Reconfigure messages it receives.
NEW:
Upon receipt of a valid Reconfigure message, the client responds with
a Renew message, a Rebind message, or an Information-request message
as indicated by the Reconfigure Message option (as defined in Section
3 of RFC 6644). The client ignores the transaction-id field in the
received Reconfigure message. While the transaction is in progress,
the client silently discards any Reconfigure messages it receives.
Section 19.4.2:
ADD new second and third paragraphs:
When responding to a Reconfigure, the client creates and sends the
Rebind message in exactly the same manner as outlined in Section
18.1.4 of RFC 3315, with the exception that the client copies the
Option Request option and any IA options from the Reconfigure message
into the Rebind message.
If a client is currently sending Rebind messages, as described in
Section 18.1.4 of RFC 3315, the client ignores any received
Reconfigure messages.
Evans, et al. Standards Track [Page 7]
RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
Section 19.4.4:
OLD:
The client uses the same variables and retransmission algorithm as it
does with Renew or Information-request messages generated as part of
a client-initiated configuration exchange. See sections 18.1.3 and
18.1.5 for details. If the client does not receive a response from
the server by the end of the retransmission process, the client
ignores and discards the Reconfigure message.
NEW:
The client uses the same variables and retransmission algorithm as it
does with Renew, Rebind, or Information-request messages generated as
part of a client-initiated configuration exchange. See Sections
18.1.3, 18.1.4, and 18.1.5 of RFC 3315 for details. If the client
does not receive a response from the server by the end of the
retransmission process, the client ignores and discards the
Reconfigure message.
6. Clarification of Section 19.4.2, RFC 3315
When sending a Renew message in response to the receipt of a
Reconfigure message, the client MUST include a Server Identifier
option, identifying the server with which the client most recently
communicated.
7. Security Considerations
This document allows the Rebind message type to appear in the
Reconfigure Message option of a Reconfigure message so that the
client rebinds to a different DHCPv6 server. A malicious attacker
may use a faked Reconfigure message to force the client to disconnect
from the current server and relink to a faked server by quickly
responding to the client's Rebind message. A similar attack is
available in DHCPv6 by an attacker spoofing itself as a valid DHCPv6
server in response to a Solicit or Request message. These attacks
can be prevented by using the AUTH option [RFC3315]. DHCPv6 clients
that support Reconfigure-Rebind MUST implement the Reconfigure Key
authentication protocol as described in [RFC3315], Section 21.5.
Other authentication mechanisms may optionally be implemented. For
example, the Secure DHCPv6 [SEC-DHCPv6], based on Cryptographically
Generated Addresses (CGA) [RFC3972], can provide source address (for
the DHCP server/relay) ownership validation, message origin
authentication, and message integrity without requiring symmetric key
pairs or support from a key management system.
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RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
8. Acknowledgements
Valuable comments were made by Jari Arkko, Sean Turner, Ted Lemon,
and Stephen Farrell.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
9.2. Informative References
[SEC-DHCPv6]
Jiang, S. and S. Shen, "Secure DHCPv6 Using CGAs", Work in
Progress, March 2012.
Evans, et al. Standards Track [Page 9]RFC 6644 DHCPv6 Reconfigure with Rebind July 2012
Authors' Addresses
D. R. Evans
IPfonix, Inc.
330 WCR 16 1/2
Longmont, CO 80504-9467
USA
Phone: +1 303.682.2412
EMail: N7DR@ipfonix.com
Ralph Droms
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Phone: +1 978.936.1674
EMail: rdroms@cisco.com
Sheng Jiang
Huawei Technologies Co., Ltd
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
EMail: jiangsheng@huawei.com
Evans, et al. Standards Track [Page 10]
