Internet DRAFT - draft-ietf-dhc-triggered-reconfigure
draft-ietf-dhc-triggered-reconfigure
DHC Working Group M. Boucadair
Internet-Draft X. Pougnard
Intended status: Standards Track France Telecom
Expires: November 16, 2013 May 15, 2013
Reconfigure Triggered by DHCPv6 Relay Agents
draft-ietf-dhc-triggered-reconfigure-07
Abstract
This document defines new DHCPv6 messages: Reconfigure-Request and
Reconfigure-Reply. Reconfigure-Request message is sent by a DHCPv6
relay agent to notify a DHCPv6 server about a configuration
information change, so that the DHCPv6 server can send a Reconfigure
message accordingly. Reconfigure-Reply message is used by the server
to acknowledge the receipt of Reconfigure-Request.
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
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This Internet-Draft will expire on November 16, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4
5. Link Address Option . . . . . . . . . . . . . . . . . . . . . 6
6. Detailed Specification . . . . . . . . . . . . . . . . . . . 7
6.1. Messages Format . . . . . . . . . . . . . . . . . . . . . 7
6.2. Messages Validation . . . . . . . . . . . . . . . . . . . 7
6.2.1. RECONFIGURE-REQUEST . . . . . . . . . . . . . . . . . 7
6.2.2. RECONFIGURE-REPLY . . . . . . . . . . . . . . . . . . 7
6.3. Creation and Transmission of RECONFIGURE-REQUEST . . . . 8
6.4. Intermediate Relay Agents Behavior . . . . . . . . . . . 9
6.5. Server Behavior . . . . . . . . . . . . . . . . . . . . . 9
6.6. Receipt of RECONFIGURE-REPLY . . . . . . . . . . . . . . 10
7. Rate Limiting Considerations . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
This document specifies two new DHCPv6 messages [RFC3315]:
Reconfigure-Request and Reconfigure-Reply.
Section 3 describes a typical problem encountered to trigger the
DHCPv6 server to issue a Reconfigure message when the configuration
data is supplied by the relay agent. This problem may be encountered
in other contexts. It is out of scope of this document to list all
these cases.
Section 4 describes the proposed solution which relies on the use of
Reconfigure-Request and Reconfigure-Reply messages. Reconfigure-
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Request message is sent by a DHCPv6 relay agent to notify a DHCPv6
server about a configuration information change, so that the DHCPv6
server can send a Reconfigure message accordingly. Reconfigure-Reply
message is used by the server to acknowledge the receipt of
Reconfigure-Request.
Section 6 provides the detailed specification of the procedure to
trigger Reconfigure messages by DHCPv6 relay agents.
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. Problem Statement
For cases where the DHCPv6 relay agent possesses some information
that would be useful to the DHCPv6 client, [RFC6422] specifies a
mechanism whereby the DHCPv6 relay agent can provide such information
to the DHCPv6 server, which can, in turn, pass this information on to
the DHCP client. This is achieved owing to the use of RSOO (Relay-
Supplied Options option) which carries configuration data to the
DHCPv6 server. The data conveyed in an RSOO is then sent back by the
DHCPv6 server to the requesting DHCPv6 client.
An example of a RSOO context is shown in Figure 1; only a subset of
exchanged DHCPv6 and RADIUS messages is represented. Figure 1 shows
a broadband network scenario in which the Network Access Server (NAS)
embeds a DHCPv6 relay agent.
+-------+ +-------+ +-------+
|DHCPv6 | | NAS | |Radius |
|Client | |(DHCPv6| |Server |
| | | Relay)| | |
+-------+ +-------+ +-------+
| | |
|---Solicit---------------->| |
| |---Access-Request---------->|
|<--Access-Accept------------|
| (e.g. DS-Lite-Tunnel-Name)|
....
| +-------+
| |DHCPv6 |
| |Server |
| | |
| +-------+
| |
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|---Relay-Forward----------->|
| (RSOO(OPTION_AFTR_NAME)) |
| |
| |<--Relay-Reply--------------|
|<--Advertise---------------| (e.g., OPTION_AFTR_NAME) |
| (e.g., OPTION_AFTR_NAME) |
....
Figure 1: An Example of the RSOO Option Usage
A configuration change may result in an exchange of CoA (Change-of-
Authorization, [RFC5176]) messages between the NAS/DHCPv6 relay agent
and Dynamic Authorization Client (DAC) server as shown in Figure 2.
In this example, the NAS answers with a CoA-Ack message to notify the
DAC the CoA-Request is successfully handled.
Note the change of the configuration in the DHCPv6 relay agent can be
triggered by any other out-of-band mechanism.
+-------+ +-------+ +-------+
|DHCPv6 | | NAS | |Radius |
|Client | |(DHCPv6| |Server/|
| | | Relay)| | DAC |
+-------+ +-------+ +-------+
| | |
|<-----CoA-Request-----------|
| (e.g. DS-Lite-Tunnel-Name) |
|------CoA-Ack-------------->|
....
Figure 2: Change of configuration
Whenever the configuration information sent by the DHCPv6 relay agent
to the DHCPv6 server change, the DHCPv6 server has no means to detect
the change so that it can send a Reconfigure message accordingly. A
solution is sketched in Section 4.
4. Solution Overview
To solve the problem described in Section 3, this document proposes a
new DHCP message called Reconfigure-Request. In the example depicted
in Figure 3, a Reconfigure-Request message is sent by the DHCPv6
relay agent to a DHCPv6 server as soon as the configuration data
conveyed in an RSOO option have changed. Upon receipt of this
message, and if it is configured to support such mode, the DHCPv6
server must build Reconfigure-Reply and Reconfigure messages.
Reconfigure-Reply is used to acknowledge the receipt of Reconfigure-
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Request. Reconfigure message encapsulated in Relay-Reply is sent to
the DHCPv6 relay, which in turn will forward the message to the
appropriate DHCPv6 client.
This setup assumes the relay has a record of the client, so that it
has enough information to send the Reconfigure-Request message to the
server. How the state is recorded in the relay is out of scope. For
better resilience of the proposed solution, means to recover state in
failure events (e.g., use of stable storage, DHCPv6 Bulk Leasequery
[RFC5460]) need to be supported. These state recovery solutions are
not discussed in this document.
+-------+ +-------+ +-------+
|DHCPv6 | | NAS | |Radius |
|Client | |(DHCPv6| |Server/|
| | | Relay)| | DAC |
+-------+ +-------+ +-------+
| | |
|<-----CoA-Request-----------|
| (e.g. DS-Lite-Tunnel-Name) |
| |
|------CoA-Ack-------------->|
....
| +-------+
| |DHCPv6 |
| |Server |
| | |
| +-------+
| |
|---Reconfigure-Request----->|
|<--Reconfigure-Reply--------|
| |
| |<--Relay-Reply -------------|
|<--Reconfigure-------------| (Reconfigure) |
| | |
....
Figure 3: Flow Example with Reconfigure-Request
The support of Reconfigure-Reply simplifies the retransmission
procedure of the relay as it provides an explicit indication from the
server (see Section 6.3 for more details). An alternative approach
is the relay monitors Reconfigure messages received from the server
to conclude whether Reconfigure-Request was successfully handled or
not. Nevertheless, this implicit approach may fail to achieve its
goals in some cases: e.g., the server accepts the request but it
delays to generate the corresponding Reconfigure messages due to its
rate-limiting policies, the request was partially failed for some
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clients, etc. To avoid useless reconfigure cycles (e.g., due to the
loss of Reconfigure-Reply), the approach adopted in this document
allows the relay to correct the content of a re-transmitted
Reconfigure-Request based on some observed events (e.g., the client
has retrieved the updated configuration). If the relay has no client
to be reconfigured, it stops sending Reconfigure-Request messages.
The Reconfigure-Request message can also be used in other scenarios
than those that assume the use of RSOO. It is out of scope of this
document to describe all these scenarios.
5. Link Address Option
Figure 4 shows the format of the Link Address Option.
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_LINK_ADDRESS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| link-address (IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Message Format of Link Address Option
The description of the fields are as follows:
option-code: OPTION_LINK_ADDRESS (To be assigned by IANA, see
Section 8).
option-len: 16 (octets).
link-address: An IPv6 address used by the server to identify the
link on which the client is located.
The Link Address Option is used by the relay agent to indicate to the
server the link on which the client is located. The relay agent MUST
use a link-address value that is equivalent to the value used when
relaying messages from the client to the server. Two link-address
values are said to be equivalent if both values are IPv6 addresses
that are on-link for the network link to which the client is
connected.
To defend against poor implementations that do not correctly evaluate
equivalence, the relay agent SHOULD use the same value that was sent
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to the DHCPv6 server when relaying messages from the client to the
server, as in Section 20.1.1 of [RFC3315].
6. Detailed Specification
6.1. Messages Format
Two new message type codes are defined:
o RECONFIGURE-REQUEST (To be assigned by IANA, see Section 8).
o RECONFIGURE-REPLY (To be assigned by IANA, see Section 8).
RECONFIGURE-REQUEST and RECONFIGURE-REPLY use the same format as
defined in Section 6 of [RFC3315].
6.2. Messages Validation
6.2.1. RECONFIGURE-REQUEST
Clients MUST silently discard any received RECONFIGURE-REQUEST
messages.
Servers MUST discard any received RECONFIGURE-REQUEST messages that
meet any of the following conditions:
o the message does not include a Client Identifier Option [RFC3315].
o the message does not include a Link Address Option (Section 5).
o the message includes a Server Identifier Option [RFC3315] but the
contents of the Server Identifier Option does not match the
server's identifier.
6.2.2. RECONFIGURE-REPLY
Clients and Servers MUST silently discard any received RECONFIGURE-
REPLY messages.
The relay MUST silently discard any received RECONFIGURE-REPLY
messages that meet any of the following conditions:
o the "transaction-id" field in the message does not match the value
used in the original message.
o the message does not include a Server Identifier Option.
o the message does not include a Status Code Option [RFC3315].
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6.3. Creation and Transmission of RECONFIGURE-REQUEST
For any event (e.g., modification of the configuration information)
that requires the server to issue a Reconfigure message, the relay
agent determines the client(s) affected by the change and then builds
a Reconfigure-Request message: the relay agent sets the "msg-type"
field to RECONFIGURE-REQUEST, generates a transaction ID and inserts
it in the "transaction-id" field.
The relay agent MUST include one or more Client Identifier Options
[RFC3315] and a Link Address Option (Section 5) so that the DHCPv6
server can identify the corresponding client and the link on which
the client is located.
The relay agent MAY include a Relay Identifier Option [RFC5460].
The relay agent MAY supply the updated configuration in the RSOO
[RFC6422]. The relay agent MAY supply a Reconfigure Message Option
to indicate which form of Reconfigure to use. The relay agent MAY
include any option (e.g., Interface Identifier [RFC3315]) which it
might insert when relaying a message received from a client.
When several clients on the same link are affected by a configuration
change, the relay MUST include several Client Identifier Options,
each of them identifies a specific client. If including Client
Identifier Options of all impacted clients exceeds the maximum
message size (see Section 7), the relay MUST generate several
RECONFIGURE-REQUEST messages required to carry all Client Identifier
Options. Rate-limit considerations are discussed in Section 7.
The relay sets the destination address of the RECONFIGURE-REQUEST
message to the IP address it would have sent a Relay-Forw message
(see Section 20 of [RFC3315]).
In case multiple servers are configured to the relay agent, several
RECONFIGURE-REQUEST messages are to be built. The behavior of the
relay agent to disambiguate responses when multiple servers are
configured is implementation-specific. For example, an
implementation may generate distinct "transaction-id"s per server
while another implementation may use the content of the "transaction-
id" field and the Server Identifier Option to disambiguate the
responses.
The relay transmits RECONFIGURE-REQUEST messages according to
Section 14 of [RFC3315], using the following parameters:
IRT 1 sec
MRT 10 secs
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MRC 5
MRD 0
The relay MAY remove clients from the client identifier list in
subsequent retransmissions, but MUST NOT add clients to the client
identifier list. This decision is local to the relay (e.g., it may
be based on observed events such as one or more clients were
reconfigured on their own).
The relay may receive Reconfigure encapsulated in Relay-Reply before
Reconfigure-Reply. The relay SHOULD NOT interpret it as if the
Reconfigure-Request was successfully handled by the Server. The
relay SHOULD use Reconfigure-Reply, not the Reconfigure message, to
determine if the request was successful (see the discussion in
Section 4) .
6.4. Intermediate Relay Agents Behavior
The relay agent MUST be configurable to accept or reject RECONFIGURE-
REQUEST messages received from other relay agents. If no indication
is explicitly configured to the relay, the default behavior is to
accept RECONFIGURE-REQUEST messages.
If the relay is configured not to allow RECONFIGURE-REQUEST messages,
the relay MUST silently discard any RECONFIGURE-REQUEST message it
receives. If the relay is configured to accept RECONFIGURE-REQUEST
messages, these messages are relayed as specified in Section 20.1.1
of [RFC3315].
6.5. Server Behavior
The server MUST be configurable to accept or reject RECONFIGURE-
REQUEST messages. If no indication is explicitly configured to the
server, the default behavior is to reject RECONFIGURE-REQUEST
messages.
Upon receipt of a valid RECONFIGURE-REQUEST message from a DHCPv6
relay agent (see Section 6.2), the server determines the client(s)
for which a Reconfigure message is to be sent.
The server constructs a Reconfigure-Reply message by setting the
"msg-type" field to RECONFIGURE-REPLY, and copying the transaction ID
from the RECONFIGURE-REQUEST message into the "transaction-id" field.
The server includes its server identifier in a Server Identifier
Option. The server MUST include a Status Code Option [RFC3315]
indicating whether the request is successfully processed, failed or
partially failed.
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o If the server fails to process the request, the server MUST set
the Status Code Option to the appropriate status code (e.g.,
UnspecFail, NotAllowed, etc.). In particular,
* UnspecFail MUST be returned if Reconfigure-Request message is
malformed.
* NotAllowed MUST be returned if the server is not configured to
allow Reconfigure-Request.
* NotConfigured MUST be returned if the server has no record of
the link [RFC5007].
o If the RECONFIGURE-REQUEST is successfully validated, the server
MUST return a Status Code Option indicating "Success". In
addition, the server MUST include a list of all the Client
Identifier Options of the clients to which Reconfigure messages
will not be sent (e.g., the server has no record of the client or
the client did not negotiate for Reconfigure support). Note that
this means that "Success" will be returned even if Reconfigure
messages will not be sent to any of the clients.
If RSOO is supplied, the server might use its content to double check
whether a Reconfigure is required to be sent to the client. This
assumes the server stored the content of RSOO it used to generate
configuration data sent to requesting clients.
The server might use the content of the Reconfigure Message Option
supplied by the relay agent to determine which form of Reconfigure to
use.
Then, the server MUST follow the procedure defined in Section 19.1 of
[RFC3315] to construct a Reconfigure message.
Rate-limit considerations are discussed in Section 7.
6.6. Receipt of RECONFIGURE-REPLY
Depending on the status code enclosed in a received RECONFIGURE-REPLY
message, the relay may decide to terminate the request (e.g.,
NotAllowed, NotConfigured, and Success) or try a different corrected
RECONFIGURE-REQUEST (e.g., UnspecFail).
When multiple servers are configured, the relay should expect to
receive several RECONFIGURE-REPLY messages. As mentioned in
Section 6.3, the relay should be able to disambiguate these responses
and associate them with a given server. The relay agent assumes the
request is successfully handled for a client if there is at least one
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Reconfigure-Reply message in which the corresponding Client
Identifier Option does not appear.
7. Rate Limiting Considerations
The relay MUST rate-limit RECONFIGURE-REQUEST messages to be sent to
the server. The relay MUST be configured with required rate-limit
parameters. The maximum RECONFIGURE-REQUEST packet size SHOULD be
configurable and the default value MUST be 1280 octets.
The server MUST rate-limit Reconfigure messages triggered by
RECONFIGURE-REQUEST messages. The server MUST be configured with
required rate-limit parameters.
8. IANA Considerations
IANA is requested to assign the following new DHCPv6 Message type in
the registry maintained in http://www.iana.org/assignments/
dhcpv6-parameters:
RECONFIGURE-REQUEST
RECONFIGURE-REPLY
IANA is requested to assign the following new DHCPv6 Option Codes in
the registry maintained in http://www.iana.org/assignments/
dhcpv6-parameters:
OPTION_LINK_ADDRESS
9. Security Considerations
Security considerations elaborated in [RFC3315] (in particular
Section 21.1) and [RFC6422] must be taken into account. In addition,
DHCPv6 servers MAY be configured to reject relayed RECONFIGURE-
REQUEST messages or restrict relay chaining (see [RFC5007] for more
discussion about the rationale of this recommended behavior).
Section 6.5 specifies the error code to return when the server is
configured to reject RECONFIGURE-REQUEST messages.
Relay agents SHOULD implement appropriate means to prevent using
RECONFIGURE-REQUEST messages as a denial-of-service attack on the
DHCPv6 servers.
Because RECONFIGURE-REQUEST message provides a mechanism for
triggering the DHCPv6 Reconfigure message, and the DHCPv6 Reconfigure
message can raise security threats (e.g., to control the timing of a
DHCPv6 renewal), the DHCPv6 server MUST have some mechanism for
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determining that the relay agent is a trusted entity. DHCPv6 servers
and relay agents MUST implement relay message authentication as
described in Section 21.1 of [RFC3315]. DHCPv6 servers MAY also
implement a control policy based on the content of received Relay
Identifier Option [RFC5460]. Administrators are strongly advised to
configure one of these security mechanisms.
In an environment where the network connecting the relay agent to the
DHCPv6 server is physically secure and does not contain devices not
controlled by the server administrator, it may be sufficient to trust
the Relay Agent Identifier provided by the relay agent. In networks
where the security of the machines with access to the data path is
not under the control of the server administrator, IPsec [RFC4301] is
necessary to prevent spoofing of RECONFIGURE-REQUEST messages.
DHCPv6 servers MUST silently discard RECONFIGURE-REQUEST messages
originating from unknown relay agents.
10. Acknowledgements
Many thanks to R. Maglione, A. Kostur, G. Halwasia, C. Jacquenet,
B. Leiba, R. Sparks, A. Farrel, B. Claise, J. Jaeggli, and P.
Resnick for the comments and review.
Special thanks to T. Lemon, B. Volz and T. Mrugalski who provided
a detailed review.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", RFC
6422, December 2011.
11.2. Informative References
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC5007] Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
"DHCPv6 Leasequery", RFC 5007, September 2007.
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[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 5176,
January 2008.
[RFC5460] Stapp, M., "DHCPv6 Bulk Leasequery", RFC 5460, February
2009.
Authors' Addresses
Mohamed Boucadair
France Telecom
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Xavier Pougnard
France Telecom
Lannion
France
Email: xavier.pougnard@orange.com
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