DHC Working Group M. Boucadair
Internet-Draft X. Pougnard
Updates: 3315, 6422 (if approved) France Telecom
Intended status: Standards Track January 21, 2013
Expires: July 25, 2013
RECONFIGURE Triggered by DHCPv6 Relay Agents
draft-ietf-dhc-triggered-reconfigure-03
Abstract
This document defines new DHCPv6 messages: Reconfigure-Request and
Reconfigure-Ack. 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.
This document updates RFC 3315 and RFC 6422.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Problem . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 4
3. Link Address Option . . . . . . . . . . . . . . . . . . . . . 6
4. RECONFIGURE-REQUEST and RECONFIGURE-ACK . . . . . . . . . . . 6
4.1. Messages Format . . . . . . . . . . . . . . . . . . . . . 6
4.2. Messages Validation . . . . . . . . . . . . . . . . . . . 7
4.2.1. RECONFIGURE-REQUEST . . . . . . . . . . . . . . . . . 7
4.2.2. RECONFIGURE-ACK . . . . . . . . . . . . . . . . . . . 7
4.3. Creation and Transmission of RECONFIGURE-REQUEST . . . . . 8
4.4. Server Behaviour . . . . . . . . . . . . . . . . . . . . . 9
4.5. Receipt of RECONFIGURE-ACK . . . . . . . . . . . . . . . . 10
5. Rate Limiting Considerations . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
1.1. Problem
[RFC6422] updates the DHCPv6 specification [RFC3315] with a new
feature to let a DHCPv6 relay agent communicate information towards a
DHCPv6 Client, and which is not available at the DHCPv6 server. 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.
+-------+ +-------+ +-------+
|DHCPv6 | | NAS | |Radius |
|Client | |(DHCPv6| |Server |
| | | Relay)| | |
+-------+ +-------+ +-------+
| | |
|---Solicit---------------->| |
| |---Access-Request---------->|
|<--Access-Accept------------|
| (e.g. DS-Lite-Tunnel-Name)|
....
| +-------+
| |DHCPv6 |
| |Server |
| | |
| +-------+
| |
|---Relay-Forward----------->|
| (RSOO(DS-Lite-Tunnel-Name))|
| |
| |<--Relay-Reply--------------|
|<--Advertise---------------|
| (e.g., OPTION_AFTR_NAME) |
....
Figure 1: An Example of the RSOO Option Usage
The change of the configuration may result in RADIUS exchanges
([RFC5176]) between the NAS/DHCPv6 relay agent and Dynamic
Authorization Client (DAC) server as shown in Figure 2. Note the
change of the configuration in the DHCPv6 relay agent can be
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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-Response--------->|
....
CoA (Change-of-Authorization, [RFC5176])
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
it so that it can send a Reconfigure message with the updated
configuration data accordingly. A solution is sketched in Section 2.
1.2. 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].
2. Proposed Solution
To solve the problem described in Section 1.1, 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-Ack and Reconfigure messages.
Reconfigure-Ack is used to acknowledge the receipt of Reconfigure-
Request. Reconfigure message is then 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. Means to recover state in failure events must be supported,
but are not discussed in this document.
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+-------+ +-------+ +-------+
|DHCPv6 | | NAS | |Radius |
|Client | |(DHCPv6| |Server/|
| | | Relay)| | DAC |
+-------+ +-------+ +-------+
| | |
|<-----CoA-Request-----------|
| (e.g. DS-Lite-Tunnel-Name) |
| |
|------CoA-Response--------->|
....
| +-------+
| |DHCPv6 |
| |Server |
| | |
| +-------+
| |
|---Reconfigure-Request----->|
|<--Reconfigure-Ack----------|
| |
| |<--Relay-Reply -------------|
|<--Reconfigure-------------| (Reconfigure) |
| | |
....
Figure 3: RECONFIGURE-REQUEST Flow Example
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.
The support of Reconfigure-Ack simplifies the retransmission
procedure of the relay as it provides an explicit indication from the
server. 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 clients, etc. To avoid
useless reconfigure cycles (e.g., due to the loss of Reconfigure-
Ack), 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 reconfigured, it stops
sending Reconfigure-Request messages.
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3. 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 6).
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. The relay agent SHOULD use the same value that was sent
to the DHCP server when relaying messages from the client to the
server, as in Section 20.1.1 of [RFC3315].
4. RECONFIGURE-REQUEST and RECONFIGURE-ACK
4.1. Messages Format
Two new message type codes are defined:
RECONFIGURE-REQUEST (To be assigned by IANA, see Section 6).
RECONFIGURE-ACK (To be assigned by IANA, see Section 6).
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RECONFIGURE-REQUEST and RECONFIGURE-ACK use the same format as
defined in Section 6 of [RFC3315].
4.2. Messages Validation
4.2.1. RECONFIGURE-REQUEST
Clients MUST silently discard any received RECONFIGURE-REQUEST
messages.
Servers MUST silently 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 3).
o the message includes a Server Identifier Option [RFC3315] but the
contents of the Server Identifier Option does not match the
server's identifier.
The server MUST be configurable to accept or reject RECONFIGURE-
REQUEST messages. If the server is configured to reject RECONFIGURE-
REQUEST, the server MUST silently discard any RECONFIGURE-REQUEST it
receives.
The relay agent MUST be configurable to accept or reject RECONFIGURE-
REQUEST messages received from other relay agents. If the relay is
configured to reject RECONFIGURE-REQUEST, the relay MUST silently
discard any RECONFIGURE-REQUEST 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].
Because RECONFIGURE-REQUEST message provides a mechanism for
triggering the DHCP Reconfigure message, and the DHCP Reconfigure
message can raise security threats (e.g., to control the timing of a
DHCP renewal), the DHCP server MUST have some mechanism for
determining that the relay agent is a trusted entity. RECONFIGURE-
REQUEST messages originating from unknown relay agents MUST be
silently dropped.
4.2.2. RECONFIGURE-ACK
Clients and Servers MUST silently discard any received RECONFIGURE-
ACK messages.
The relay MUST silently discard any received RECONFIGURE-ACK messages
that meet any of the following conditions:
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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].
4.3. 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 which is 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 a Client Identifier Option [RFC3315] and a Link Address
Option (Section 3) so that the DHCPv6 server can identify the
corresponding client and the link on which the client is located.
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 5), the relay MUST generate several
RECONFIGURE-REQUEST messages required to carry all Client Identifier
Options. Rate-limit considerations are discussed in Section 5.
The relay transmits RECONFIGURE-REQUEST messages according to Section
14 of [RFC3315], using the following parameters:
IRT 1 sec
MRT 10 secs
MRC 5
MRD 0
When retransmission is required, the relay may decide to correct the
content of RECONFIGURE-REQUEST message it issues (e.g., update 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 (Relay-Reply) Reconfigure before Reconfigure-
Ack. The relay SHOULD NOT interpret it as if the Reconfigure-Request
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was successfully handled by the Server. The relay SHOULD use
Reconfigure-Ack, not the Reconfigure message, to determine if the
request was successful.
4.4. Server Behaviour
Upon receipt of a valid Reconfigure-Request message from a DHCPv6
relay agent (see Section 4.2), the server determines the client(s)
for which a Reconfigure message is to be sent.
The server constructs a Reconfigure-Ack message by setting the "msg-
type" field to RECONFIGURE-ACK, and copying the transaction ID from
the RECONFIGURE-REQUEST message into the transaction-id field. The
server MUST include a Status Code Option [RFC3315] indicating whether
the request is successfully processed, failed or partially failed.
o If the request is successfully handled by the server, the server
MUST include a Status Code Option indicating "Success".
o If the request includes several Client Identifier options but the
server will issue reconfigure requests only for a subset of them,
the server MUST include a Status Code Option indicating "Success"
but in the meantime it MUST copy back the list of Client
Identifier Options pointing to clients for which the server won't
issue a Reconfigure message.
o If the server failed to process the request for all clients, the
server MUST set the Status Code Option to the appropriate status
code (e.g., UnspecFail, NotAllowed, etc.).
If RSOO is supplied, the server MAY use its content to double check
whether a Reconfigure is required to be sent to the client. This
assumes the server store the content of RSOO it used to generate
configuration data sent to requesting clients.
The server MAY 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. This Reconfigure
message may be sent directly to the DHCPv6 client or to a relay agent
[RFC3315].
Rate-limit considerations are discussed in Section 5.
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4.5. Receipt of RECONFIGURE-ACK
Depending on the status code enclosed in a received RECONFIGURE-ACK
message, the relay may decide to terminate the request or try a
different corrected Reconfigure-Request.
5. 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 (i.e., the rate of Reconfigure messages). 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 (i.e., the rate of Reconfigure
messages).
6. 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-ACK
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
7. 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 discard relayed RECONFIGURE-
REQUEST messages or restrict relay chaining (see [RFC5007] for more
discussion about the rationale of this recommended behavior). Relay
agents SHOULD implement appropriate means to prevent using
RECONFIGURE-REQUEST messages as a denial-of-service attack on the
DHCPv6 servers.
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8. Acknowledgements
Many thanks to R. Maglione, A. Kostur, G. Halwasia, C. Jacquenet and
B. Volz for the comments and review.
Special thanks to T. Lemon who provided a detailed review.
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., 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.
9.2. Informative References
[RFC5007] Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
"DHCPv6 Leasequery", RFC 5007, September 2007.
[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.
Authors' Addresses
Mohamed Boucadair
France Telecom
Rennes, 35000
France
Email: mohamed.boucadair@orange.com
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Xavier Pougnard
France Telecom
Lannion,
France
Phone:
Email: xavier.pougnard@orange.com
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