Internet DRAFT - draft-gandhewar-dhc-v6-relay-initiated-release
draft-gandhewar-dhc-v6-relay-initiated-release
dhc Working Group S. Gandhewar
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track October 1, 2015
Expires: April 3, 2016
DHCPv6 Relay Initiated Release
draft-gandhewar-dhc-v6-relay-initiated-release-01
Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) is
initiated by a DHCPv6 client. A DHCPv6 server can force DHCPv6
client to send RENEW or INFORMATION-REQUEST by sending a RECONFIGURE
message. There may be multiple DHCPv6 network devices connected in
between a DHCPv6 client and a server, each one reserving resources
for the DHCPv6 client. There are no DHCPv6 messages that a relay can
initiate in order to control the client binding.
A DHCPv6 client may not always send a RELEASE message when it no
longer needs the IPv6 address or prefix and network resources for the
associated services it is using. This document specifies a way to
request release to be initiated by an intermediate DHCPv6 network
device, e.g. DHCPv6 relay, on behalf of DHCPv6 client. This helps
to relinquish network resources sooner than the lease expiration
time.
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 April 3, 2016.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Problem Description . . . . . . . . . . . . . . . . . . . 3
1.2. Relay Initiated Release . . . . . . . . . . . . . . . . . 4
1.3. Applicability . . . . . . . . . . . . . . . . . . . . . . 5
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 7
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Message Definitions . . . . . . . . . . . . . . . . . . . 7
3.1.1. RELEASE-REQUEST . . . . . . . . . . . . . . . . . . . 7
3.1.2. RELEASE-REQUEST-REPLY . . . . . . . . . . . . . . . . 8
3.2. Message Validation . . . . . . . . . . . . . . . . . . . 8
3.2.1. RELEASE-REQUEST . . . . . . . . . . . . . . . . . . . 8
3.2.2. RELEASE-REQUEST-REPLY . . . . . . . . . . . . . . . . 9
4. Functionality . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. First DHCPv6 Network Device Behavior . . . . . . . . . . 9
4.1.1. Generation and Transmission of RELEASE-REQUEST
Message . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.2. Receipt of RELEASE-REQUEST Message . . . . . . . . . 11
4.2. Intermediate DHCPv6 Network Device Behavior . . . . . . . 11
4.3. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . 11
4.4. Receipt of RELEASE-REQUEST-REPLY . . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
DHCPv6 [RFC3315] and [RFC3633] provides a framework for configuring
clients with network addresses, address prefixes and other network
parameters. It includes a relay agent capability where DHCPv6 server
may not be directly connected to the DHCPv6 client. A relay agent is
an intermediate node that passes DHCPv6 messages between DHCPv6
clients and DHCPv6 servers. As per [RFC3315], a relay agent cannot
generate a message on its own which can control the client binding.
Figure 1 below shows a typical network with multiple DHCPv6 devices.
+---------+ +---------+ +---------+ +---------+
| DHCPv6 |-----| DHCPv6 |--...--| DHCPv6 |-----| DHCPv6 |
| Server | | Relay n | | Relay 1 | | Client |
+---------+ +---------+ +---------+ +---------+
Figure 1: Typical DHCPv6 Network
1.1. Problem Description
While providing an IPv6 address or IPv6 Prefix to the DHCPv6 Client,
Service Providers (e.g. Broadband Service Providers), creates a
logical interface per client, programs various routes (e.g. access
routes, framed routes) for the client to access the network and
services, attaches services (e.g. voice, video, data), maintains
policy, applies QoS. Along with these resources there is a need for
memory and bandwidth per client. Since all these resources are
limited on a network device (e.g. Broadband Network Gateway), it
defines the scaling capacity of the device. Since the availability
of the IPv6 addresses is large, subscription rate for the Service
Providers is thus limited by the availability of the resources on
their network device.
A DHCPv6 client may be connected to the DHCPv6 server through
multiple DHCPv6 network devices, e.g. multiple DHCPv6 relays. These
network resources remain reserved for the client at all the DHCPv6
network devices until the lease expires.
In some situations, there might be need to clear the client binding
administratively. The process of administratively clearing the
client binding is very cumbersome. The administrator needs to access
every single DHCPv6 network device (relay, relay-proxy) and also the
DHCPv6 server, and clear the DHCPv6 client binding at each of these
devices manually.
In some situations when the DHCPv6 client is replaced (e.g. replacing
the set-top-box) due to the device failure or upgrade, the older
DHCPv6 client might not have sent the RELEASE message on its failure.
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In this case, the previously assigned IPv6 address or prefix and
network resources for the older (stale) client will stay reserved and
unused until the lease expires.
Same is the situation where clients move frequently without sending
RELEASE e.g. in the case of mobile networks, network resources stay
reserved and unused. Similarly, network resources stay reserved and
unused where DHCPv6 clients login and logout frequently without
sending RELEASE e.g. Wi-Fi access centers.
As per DHCPv6 protocol it is not mandatory for the DHCPv6 client to
send a RELEASE message while disconnecting. As per the statistics
from Service Providers, 95% of the cases DHCPv6 client does not send
RELEASE message when it no longer needs the service. It is also
possible that the UDP datagram carrying a RELEASE message may get
dropped due to network issues.
All the resources including the IPv6 address or prefix remains
reserved for the client at all the DHCPv6 network devices until the
lease expires. Service Providers needs to take into account such
situations and are forced to lower the subscription rate. Thus it
reduces the scaling per network device. Also it causes errors for
the time based billing.
1.2. Relay Initiated Release
It is possible for the first DHCPv6 network device, i.e. "DHCPv6
Relay 1" in Figure 1 which is closest to the DHCPv6 client, to detect
that the DHCPv6 client is replaced, moved or is no longer present on
the network. In this scenario, the relay agent doesn't have any
mechanism to inform the server to release the client's binding and
subsequently relinquish network resources.
With the relay initiated release message, when a DHCPv6 relay detects
client's unavailability or needs to clear the client binding
administratively, it can generate the release message on behalf of
the client and send it to the server. Thus, all the DHCPv6 network
devices along the path will be in synchronization with respect to the
client's binding information and network resources can be
relinquished earlier than the lease expiry. The server MAY choose to
integrate some mechanism to confirm with the client, e.g. generate
RECONFIGURE message before sending reply to the relay. It is outside
the scope of this document.
Generation of the relay initiated release SHOULD be a configurable
behavior at the first relay. The configuration at Relay SHOULD be
further granular to indicate the situation under which relay should
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initiate the release e.g. administratively clearing DHCPv6 binding,
client replaced, client moved, client unavailable, etc.
Forwarding of the relay initiated release related messages SHOULD be
a configurable behavior at the intermediate DHCPv6 network devices.
Acceptance of relay initiated release SHOULD also be a configurable
behavior at the server.
The purpose of such configurable behavior is explained in
Section 1.3.
1.3. Applicability
As per the statistics from Service Providers, 95% of the cases DHCPv6
client does not send RELEASE message when it no longer needs the
service. This functionality is useful in order to relinquish network
resources sooner than the lease expiry. This allows Service
Providers for higher subscription rate and accurate time based
billing.
This functionality described in Section 1.2 is useful for clearing
the client binding administratively, client replacement, frequent
client login and logout without sending RELEASE (e.g. at Wi-Fi
centers) or where client moves frequently without sending RELEASE
(e.g. mobile networks). All these situations can be detected by the
first DHCPv6 network device. Thus this functionality is applicable
to all these situations without any problems.
This functionality is also useful where client unavailability can be
detected. Client unavailability could be because of multiple
reasons. Client may become unavailable due to powered-off,
disconnect from the network or problems in the network itself. Since
it is difficult to identify the cause of client's absence, precaution
must be taken in such situations. With this functionality described
in Section 1.2, the state of the binding is cleared and network
resources are relinquished at DHCPv6 Relay, DHCPv6 Server and all the
intermediate network devices. However it is possible that the
binding is still not cleared at the DHCPv6 client. There may be a
situation where client remembers the IPv6 address or prefix as well
as the lease it received and continue to use when network comes back.
This situation may happen when the network between Relay and client
becomes unavailable and Relay may assume that the client is
unavailable.
When such a situation happens where all the DHCPv6 network devices
cleared the binding but client still remembers and tries to use the
address or prefix, at that moment there is no way to clear the
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binding at the client. The client's binding will get cleared at the
client at the time of Renew or Rebind or when the lease expires or
when client restarts DHCPv6 process.
This may not be a problem in case of DSL based networks where DHCPv6
is over PPP session. The failed PPP session will cause the DHCPv6
client to bring up the PPP session and restart the DHCPv6 discovery
process. However it may be a problem with an Ethernet based access
network since there is no trigger event to the CPE (client) to
restart the DHCPv6 binding process.
In some provider networks, DHCPv6 Relay has liveness detection. When
the network between DHCPv6 Relay and client becomes unavailable,
DHCPv6 Relay may initiate Release, whereas client is completely
unaware. It is not possible to differentiate between network
unavailable and client unavailable. This will very likely be the
case with cable network configurations. If the link between Cable
Modem and the CMTS goes down, the Relay running on CMTS may initiate
release for the Cable Modem as well as the devices behind the Cable
Modem unless Cable Modem runs the DHCPv6 Relay. The granular
configuration to initiate Release on client unavailability should be
turned off in such networks.
However, there are some Service Provider networks where DHCPv6 client
runs the liveness detection e.g. BFD on the provider facing
interface. Such DHCPv6 clients can identify the network
unavailability and may restart the DHCPv6 binding process.
In some Service Provider networks, Relay takes up longer lease from
the Server but gives out very small lease to the DHCPv6 client. This
forces DHCPv6 client to frequently renew the lease. Thus recovery
from problematic state of the DHCPv6 client will be much faster in
such network configurations.
For some of the Service Provider's configurations, DHCPv6 Relay adds
access routes per subscriber (DHCPv6 client) and remove these routes
on clearing the binding on receiving the REPLY for RELEASE or the
RELEASE-REQUEST-REPLY. Thus the Relay can restrict DHCPv6 client's
network traffic based on the source or the destination address and
thus restrict the harm and protects from two devices accessing the
network with the same IPv6 address.
This functionality SHOULD be a configurable behavior since there is
no clear way to distinguish between DHCPv6 client unavailable and
network unavailable. Having configurable behavior equips
administrator to enable this granular knob (send Relay Initiated
Release on DHCPv6 client's unavailability) at Relay only if it is
certain that such a situation will not occur or client will clear the
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binding state and reestablish or the risk of such situation is being
accounted.
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 RFC 2119 [RFC2119].
3. Protocol Details
3.1. Message Definitions
This document specifies 2 new DHCPv6 message types:
o RELEASE-REQUEST
o RELEASE-REQUEST-REPLY
The RELEASE-REQUEST and RELEASE-REQUEST-REPLY messages use the
Client/Server Message Formats described in Section 6 of [RFC3315],
similar to the LEASEQUERY and LEASEQUERY-REPLY in [RFC5007].
3.1.1. RELEASE-REQUEST
This is the relay initiated release request message.
The RELEASE-REQUEST message MAY be generated by the first DHCPv6
network device ("DHCPv6 Relay 1" in Figure 1), on behalf of the
DHCPv6 client. The RELEASE-REQUEST message MUST contain one or more
Client Data Options as described in Section 4.1.2.2 of [RFC5007],
requesting release for one or more clients.
The RELEASE-REQUEST message MUST contain the Server Identifier
Option. It MAY contain Interface-Id Option indicating common values
for all the clients requesting the release. This reduces the
redundant data when there are multiple clients with common
information.
Each Client Data Option MUST include the Client Identifier Option
OPTION_CLIENTID. It MUST also include options containing the IAs -
OPTION_IAADDR, OPTION_IAPREFIX, etc. - for the addresses or prefixes
it is releasing. If the Interface-Id option is different from the
one included directly under RELEASE-REQUEST message then it MUST be
included here.
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3.1.2. RELEASE-REQUEST-REPLY
This is the reply for the RELEASE-REQUEST message.
The message RELEASE-REQUEST-REPLY will be generated by the DHCPv6
Server to communicate the status of the request. The server conveys
the success or failure of the RELEASE-REQUEST by including Status
Code Option at different levels:
o Status Code Option directly inside RELEASE-REQUEST: Indicates
success or failure of the complete RELEASE-REQUEST message it
received.
o Status Code Option inside Client Data Option: Indicates success or
failure to release all the addresses or prefixes for a particular
client. Client Data Option MUST include the Client-Id Option.
o Status Code Option inside IA Option: Indicates success or failure
to release a particular address or prefix for a particular client.
Client Data Option MUST include the Client-Id Option and the IA
option.
The RELEASE-REQUEST-REPLY message MAY contain one or more Client Data
Options, described in Section 4.1.2.2 of [RFC5007], responding to the
request to release for each of the clients.
The RELEASE-REQUEST-REPLY message SHOULD contain the Interface-Id
option if it was included in RELEASE-REQUEST message.
3.2. Message Validation
3.2.1. RELEASE-REQUEST
Clients MUST silently discard any received RELEASE-REQUEST messages.
Relay MAY accept or discard any received RELEASE-REQUEST messages
depending upon the configuration as explained in Section 4.1.2.
Servers MUST discard any received RELEASE-REQUEST messages that meet
any of the following conditions:
o The message does not include a Relay Id Option.
o The message does not include a Client Data Option.
o The Client Data Option does not include a Client Identifier
Option.
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o The message does not include a Server Identifier option.
o The message includes a Server Identifier Option but the contents
of the Server Identifier Option do not match the server's
identifier.
3.2.2. RELEASE-REQUEST-REPLY
Clients MUST silently discard any received RELEASE-REQUEST-REPLY
messages.
Servers MUST silently discard any received RELEASE-REQUEST-REPLY
messages.
Relay MUST discard any received RELEASE-REQUEST-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 RELEASE-REQUEST message.
o The message does not include a Status Code Option.
4. Functionality
The generation of a RELEASE-REQUEST message SHOULD be a configurable
behavior at DHCPv6 network device. Similarly, taking action to
release the binding SHOULD also be a configurable behavior at the
DHCPv6 server and intermediate DHCPv6 network devices.
4.1. First DHCPv6 Network Device Behavior
Devices MAY be configured to generate the newly defined RELEASE-
REQUEST message.
The first DHCPv6 network device ("DHCPv6 Relay 1" in Figure 1) can be
configured such that when it detects the client is no longer
available on the network or is replaced or the binding information
needs to be deleted administratively, the device can generate the
RELEASE-REQUEST message.
In order to generate the RELEASE-REQUEST message this network device
needs to store the information related to the client, e.g. the client
identifier and the server identifier used while obtaining the client
lease.
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4.1.1. Generation and Transmission of RELEASE-REQUEST Message
Set the "msg-type" field to RELEASE-REQUEST.
Generate a transaction ID and insert it in the "transaction-id"
field.
MUST include Server-Id Option.
MUST include Relay-Id option [RFC5460].
MAY add Interface-Id option [RFC3315].
MUST include one or more Client Data Options each one:
o MUST include Client Identifier and MUST be same as what was used
when client obtained the lease.
o MAY include options containing the IAs (IA_NA, IA_TA, IA_PD) for
the addresses or prefixes it is requesting to be released.
Absence of this option indicates release of all the addresses and
prefixes associated with this Client Identifier.
o MAY include Interface-Id option [RFC3315] if it is different from
the one included outside of the Client Data Option
Because RELEASE-REQUEST messages MAY be lost, the message SHOULD be
retransmitted if no RELEASE-REQUEST-REPLY message is received. The
client transmits the message according to Section 14 of [RFC3315],
using the following parameters:
o IRT REL_TIMEOUT
o MRT 0
o MRC REL_MAX_RC
o MRD 0
If RELEASE-REQUEST-REPLY from a DHCPv6 server is lost, then the
RELEASE-REQUEST will be retransmitted, and the server MAY respond
with a RELEASE-REQUEST-REPLY indicating a status as NoBinding.
Therefore, in this message exchange, the relay SHOULD NOT treat a
RELEASE-REQUEST-REPLY message with a status of NoBinding as an error.
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4.1.2. Receipt of RELEASE-REQUEST Message
In order to protect against spoofed RELEASE-REQUEST messages
attempting to disconnect the clients, the first DHCPv6 network device
SHOULD drop any received RELEASE-REQUEST messages. It MUST be a
configurable behavior if these messages are from the trusted sources
and needs to be forwarded to the server.
4.2. Intermediate DHCPv6 Network Device Behavior
The behavior of the intermediate DHCPv6 network device can be
configurable to either accept or reject these messages. On
accepting, it can forward the messages as specified in Section 20.1
and 20.2 of [RFC3315].
4.3. DHCPv6 Server Behavior
DHCPv6 server ("DHCPv6 Server" in Figure 1) SHOULD be configurable to
either accept or reject the relay initiated release message RELEASE-
REQUEST. Upon receipt of a RELEASE-REQUEST message, the server MUST
confirm the validity of the message.
If server does not support the new message type then it MAY simply
drop the packet.
If the server is not configured to accept this relay initiated
RELEASE-REQUEST message then it MAY simply drop the packet or send
RELEASE-REQUEST-REPLY with status as NotConfigured.
If the server decides not to accept the RELEASE-REQUEST from a
particular relay, it MAY simply drop the packet or send RELEASE-
REQUEST-REPLY with status as NotAllowed.
The server SHOULD iterate through each of the Client Data Options and
examine the Client-Id and the addresses in the IAs for validity. If
the addresses or prefixes in the IAs have been assigned by the
server, the server deletes the binding of these addresses and
prefixes and makes them available for assignment to other clients.
Server keeps note of these addresses and prefixes in the IAs for
generating the RELEASE-REQUEST-REPLY.
After all of the clients have been processed, the server generates a
RELEASE-REQUEST-REPLY message and includes a Status Code Option with
value Success. It also includes Server Identifier option.
For each of the clients where there is a failure in releasing
addresses or prefixes, server MUST include Client Data Option. In
the Client Data Option, it MUST include the Client Identifier option
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from the RELEASE-REQUEST message. It MUST also include Status Code
Option for each of the failed IAs from the RELEASE-REQUEST message.
For the clients or IAs for which the server has no binding
information, correspondingly, the server MUST include a Status Code
Option with the value NoBinding. No other options are included in
the IA option.
4.4. Receipt of RELEASE-REQUEST-REPLY
The first DHCPv6 network device ("DHCPv6 Relay 1" in Figure 1), upon
receipt of a valid RELEASE-REQUEST-REPLY message, considers the
completion of RELEASE-REQUEST event. The action at this device is
based on the status. For all of the IAs or clients where the Status
Code is not Success or NoBinding, addresses and prefixes remain
unchanged until the lease expires. For all other clients and IAs,
bindings MUST be cleared.
5. Security Considerations
The RELEASE-REQUEST message provides a mechanism for releasing the
client binding, it can be the cause of security threat. The DHCPv6
server SHOULD have some mechanism for determining that the relay
agent is a trusted entity. DHCPv6 servers and relay agents MAY
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 a received Relay Identifier Option [RFC5460].
Administrators MAY 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 messages.
DHCPv6 servers MUST silently discard RELEASE-REQUEST messages
originating from unknown or untrusted relay agents or reject the
RELEASE-REQUEST. Section 4.3 specifies the error code to return when
the server is configured to reject RELEASE-REQUEST messages.
6. IANA Considerations
We request IANA to assign following new message types from the
registry of Message Types maintained in:
http://www.iana.org/assignments/dhcpv6-parameters/
o RELEASE-REQUEST
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o RELEASE-REQUEST-REPLY
7. Acknowledgements
We would like to acknowledge Utae Kim (Smart GiGA Network Project,
Korea Telekom), Dan Seibel (Sr. Engineer, TELUS), Ian Farrer
(Network Architect, Deutsche Telekom) and Chris Topazi (Access
Engineering, Cox Communications) for their valuable contributions,
suggestions and support for this document.
We would like to thank Bernie Volz, Ted Lemon, Andrew Sullivan, Ole
Troan and Shrivinas Joshi for their valuable comments and suggestions
for improving the document.
Many thanks to Tomek Mrugalski, Bernie Volz and Jaya Bhawtankar (Lead
Engineer, Coriant) for their support.
We would like to acknowledge Anand Vijayvergiya, Jeff Haas and Ross
Callon for their guidance and tirelessly reviewing the document
multiple times.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
8.2. Informative References
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
DOI 10.17487/RFC3633, December 2003,
<http://www.rfc-editor.org/info/rfc3633>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <http://www.rfc-editor.org/info/rfc4301>.
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[RFC5007] Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
"DHCPv6 Leasequery", RFC 5007, DOI 10.17487/RFC5007,
September 2007, <http://www.rfc-editor.org/info/rfc5007>.
[RFC5460] Stapp, M., "DHCPv6 Bulk Leasequery", RFC 5460,
DOI 10.17487/RFC5460, February 2009,
<http://www.rfc-editor.org/info/rfc5460>.
Author's Address
Sunil M. Gandhewar
Juniper Networks, Inc.
Email: sgandhewar@juniper.net
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