Internet DRAFT - draft-gandhewar-dhc-relay-initiated-release
draft-gandhewar-dhc-relay-initiated-release
dhc Working Group S. Gandhewar
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track October 1, 2015
Expires: April 3, 2016
DHCP Relay Initiated Release
draft-gandhewar-dhc-relay-initiated-release-01
Abstract
The Dynamic Host Configuration Protocol (DHCP) is initiated by a DHCP
client. A DHCP server can force DHCP client to send DHCPRENEW by
sending a DHCPFORCERENEW message. There may be multiple DHCP network
devices connected in between a DHCP client and a server, each one
reserving resources for the DHCP client. There are no DHCP messages
that a relay can initiate in order to control the client binding.
A DHCP client may not always send a DHCPRELEASE message when it no
longer needs the IP address and network resources for the associated
services it is using. This document specifies a way to request
release message to be initiated by an intermediate DHCP network
device, e.g. DHCP relay, on behalf of DHCP client. This helps to
relinquish network resources sooner than the lease expiration time.
Status of This Memo
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This Internet-Draft will expire on April 3, 2016.
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. New Message and Option Value Definitions . . . . . . . . . . 5
3.1. DHCPRELEASEBYRELAY . . . . . . . . . . . . . . . . . . . 5
3.2. DHCPRELAYREPLY . . . . . . . . . . . . . . . . . . . . . 5
3.3. NoBinding . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. NotConfigured . . . . . . . . . . . . . . . . . . . . . . 5
4. Functionality . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. First DHCP Network Device Behavior . . . . . . . . . . . 6
4.1.1. Generation and Transmission of DHCPRELEASEBYRELAY
Message . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.2. Receipt of DHCPRELEASEBYRELAY Message . . . . . . . . 7
4.1.3. Receipt of DHCPRELAYREPLY Message . . . . . . . . . . 7
4.1.4. Receiving No Response . . . . . . . . . . . . . . . . 7
4.2. DHCP Server Behavior . . . . . . . . . . . . . . . . . . 8
4.2.1. Receipt of DHCPRELEASEBYRELAY Message . . . . . . . . 8
4.2.2. Generation and Transmission of DHCPRELAYREPLY Message 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
DHCP [RFC2131] provides a framework for configuring clients with
network addresses and other network parameters. It includes a relay
agent capability where DHCP server may not be directly connected to
the DHCP client. A relay agent is an intermediate node that passes
DHCP messages between DHCP clients and DHCP servers. As per
[RFC2131], 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 DHCP devices.
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+---------+ +---------+ +---------+ +---------+
| DHCP |-----| DHCP |--...--| DHCP |-----| DHCP |
| Server | | Relay n | | Relay 1 | | Client |
+---------+ +---------+ +---------+ +---------+
Figure 1: Typical DHCP Network
While providing an IP address to the DHCP 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. Subscription rate for the Service Providers is thus limited
by the availability of the IP addresses as well as the resources on
their network device.
A DHCP client may be connected to the DHCP server through multiple
DHCP network devices, e.g. multiple DHCP relay and/or relay-proxy.
These network resources remain reserved for the client at all the
DHCP 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 DHCP network device (relay, relay-proxy) and also the
DHCP server, and clear the DHCP client binding at each of these
devices manually.
In some situations when the DHCP client is replaced (e.g. replacing
the set-top-box) due to the device failure or upgrade, the older DHCP
client might not have sent the DHCPRELEASE message on its failure.
In this case, the previously assigned IP address 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
DHCPRELEASE e.g. in the case of mobile networks, network resources
stay reserved and unused. Similarly, network resources stay reserved
and unused where DHCP clients login and logout frequently without
sending DHCPRELEASE e.g. Wi-Fi access centers.
As per DHCP protocol it is not mandatory for the DHCP client to send
a DHCPRELEASE message while disconnecting. As per the statistics
from Service Providers, 95% of the cases DHCP client does not send
DHCPRELEASE message when it no longer needs the service. It is also
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possible that the UDP datagram carrying a DHCPRELEASE message may get
dropped due to network issues.
All the resources including the IP address remain reserved for the
client at all the DHCP 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.
It is possible for the first DHCP network device, i.e. "DHCP Relay 1"
in Figure 1 which is closest to the DHCP client, to detect that the
DHCP 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 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 DHCP 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
FORCERENEW 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
initiate the release e.g. administratively clearing DHCP binding,
client replaced, client moved, client unavailable, etc.
Forwarding of the relay initiated release related messages SHOULD be
a configurable behavior at the intermediate DHCP network devices.
Acceptance of relay initiated release SHOULD also be a configurable
behavior at the server.
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].
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3. New Message and Option Value Definitions
This document specifies 2 new DHCP message types (option 53 from
Section 9.6 of [RFC2132]):
o DHCPRELEASEBYRELAY
o DHCPRELAYREPLY
The format of these messages is same as defined in [RFC2131].
This document specifies 2 new values for the Status Code Option
(option 151 from Section 6.2.2 of [RFC6926]):
o NoBinding
o NotConfigured
3.1. DHCPRELEASEBYRELAY
This message MAY be generated by the first DHCP network device ("DHCP
Relay 1" in Figure 1), on behalf of the DHCP client. This gives an
indication to the server that the client binding can be cleared.
3.2. DHCPRELAYREPLY
This is the reply from DHCP server in response to the
DHCPRELEASEBYRELAY message. The server conveys success or failure of
the DHCPRELEASEBYRELAY.
3.3. NoBinding
When the server does not find the binding for which
DHCPRELEASEBYRELAY is received, it uses this new value in the Status
Code Option.
3.4. NotConfigured
When the server is not configured to accept DHCPRELEASEBYRELAY, it
uses this new value in the Status Code Option.
4. Functionality
The generation of a DHCPRELEASEBYRELAY message SHOULD be a
configurable behavior at the DHCP relay. Taking action to release
the binding SHOULD also be a configurable behavior at the server and
intermediate DHCP network devices. Depending upon the configuration,
the server responds with DHCPRELAYREPLY
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4.1. First DHCP Network Device Behavior
Devices MAY be configured to generate the newly defined
DHCPRELEASEBYRELAY message.
The first DHCP network device ("DHCP Relay 1" in Figure 1) can be
configured such that when it detects the client is no longer on the
network or is replaced or the binding information needs to be deleted
administratively, the device can generate the DHCPRELEASEBYRELAY
message.
In order to generate the DHCPRELEASEBYRELAY message this network
device needs to store the information related to the client, e.g.
hardware address, client identifier, server identifier and giaddr
used while obtaining client lease.
4.1.1. Generation and Transmission of DHCPRELEASEBYRELAY Message
This new message is similar to the DHCPRELEASE generated by the
client, as explained in [RFC2131]. The construction of the
DHCPRELEASEBYRELAY is similar to the construction of any other DHCP
messages as described in Section 4.1 of [RFC2131]. Note that this
message is generated on behalf of the DHCP client hence all the
fields in the message MUST be with respect to the client, as if it
was generated by the client.
Set the following fields in the DHCPRELEASEBYRELAY message:
o op - MUST be set to BOOTREQUEST
o xid - MUST be filled as a random number
o chaddr - MUST be filled with hardware address of the client on
whose behalf the DHCPRELEASEBYRELAY is being sent
o ciaddr - MUST be filled with client's network address
o giaddr - MUST be filled and SHOULD be same as what was used when
client obtained the lease
Include the following options in the DHCPRELEASEBYRELAY message:
o DHCP message type - MUST be included as DHCPRELEASEBYRELAY
o Client identifier - if the client had used this option while
obtaining the lease, it MUST include this option with the same
value
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o Server identifier - MUST be included and SHOULD be same as what
was used when client obtained the lease
o Relay Agent Information Option 82 - MAY include this option
[RFC3046] with the same value as what was used while obtaining the
lease
DHCPRELEASEBYRELAY SHOULD be sent as unicast message to the server.
4.1.2. Receipt of DHCPRELEASEBYRELAY Message
In order to protect against spoofed DHCPRELEASEBYRELAY messages
attempting to disconnect the clients, the first DHCP network device
SHOULD drop any received DHCPRELEASEBYRELAY messages. It MUST be a
configurable behavior if these messages are from the trusted sources
and needs to be forwarded to the server.
4.1.3. Receipt of DHCPRELAYREPLY Message
If xid of the DHCPRELAYREPLY does not match with the xid of the
DHCPRELEASEBYRELAY which was sent, DHCPRELAYREPLY MUST be silently
dropped.
The first DHCP network device ("DHCP Relay 1" in Figure 1), upon
receipt of a valid DHCPRELAYREPLY message from the server, considers
the completion of DHCPRELEASEBYRELAY event.
The action at this device is based on the Status Code Option. In the
absence of Status Code Option or if the value is Success or
NoBinding, then this device MUST clear the binding. If the Status
Code is not Success or NoBinding, those client bindings MUST remain
until the lease expires.
If DHCPRELAYREPLY from the DHCP server is lost then the
DHCPRELEASEBYRELAY will be retransmitted, and the server MAY respond
with a DHCPRELAYREPLY indicating a Status Code as NoBinding.
Therefore, in this message exchange, the relay SHOULD NOT treat a
DHCPRELAYREPLY message with a Status Code of NoBinding as an error.
4.1.4. Receiving No Response
The DHCP relay does not receive a response from the server if the
DHCPRELEASEBYRELAY or DHCPRELAYREPLY message is lost. In such cases,
relay SHOULD resend the DHCPRELEASEBYRELAY message to the server
using a backoff algorithm for the retry time that approximates an
exponential backoff. Depending on the network bandwidth between the
relay and the server, the relay SHOULD choose a delay. This delay
grows exponentially as retransmissions fail. The number of
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retransmissions SHOULD be limited. The exponential backoff algorithm
is specified in Section 4.1 of [RFC3046].
4.2. DHCP Server Behavior
DHCP server ("DHCP Server" in Figure 1) SHOULD be configurable either
to accept or reject the newly defined DHCPRELEASEBYRELAY message.
4.2.1. Receipt of DHCPRELEASEBYRELAY Message
If the DHCP server does not support the new message type then it can
simply drop the packet.
If the server is not configured to accept this relay initiated
DHCPRELEASEBYRELAY message then it can simply drop the packet or send
DHCPRELAYREPLY with status code as NotConfigured.
The server MAY be configured to restrict itself from accepting this
message with the same giaddr which was used while obtaining the lease
(DISCOVER-OFFER_REQUEST-ACK message exchange). If server decides not
to accept the DHCPRELEASEBYRELAY message from a particular relay, it
can simply drop the packet or send DHCPRELAYREPLY with status code as
NotAllowed.
On receipt of a valid and acceptable DHCPRELEASEBYRELAY message, if
configuration allows, server MAY decide to clear the binding as
explained in Section 4.3.4 of [RFC2131]. Server MUST send a
DHCPRELAYREPLY message to the relay.
If the server does not find the binding for which it received the
DHCPRELEASEBYRELAY message, it MUST send the DHCPRELAYREPLY with
status code as Nobinding.
4.2.2. Generation and Transmission of DHCPRELAYREPLY Message
Construction of the DHCPRELAYREPLY is similar to construction of any
other DHCP messages as described in Section 4.1 of [RFC2131]. This
message is similar to DHCPACK which is generated by the server, as
explained in [RFC2131].
Set the following fields in the DHCPRELAYREPLY message:
o op - MUST be set to BOOTREPLY
o xid - MUST be copied from DHCPRELEASEBYRELAY
o chaddr - MUST be copied from DHCPRELEASEBYRELAY
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o ciaddr - MUST be filled with client's network address
o giaddr - MUST be copied from DHCPRELEASEBYRELAY
Include the following options in the DHCPRELAYREPLY message:
o DHCP message type - MUST be included as DHCPRELAYREPLY
o Client identifier - MUST be copied from DHCPRELEASEBYRELAY
o Server identifier - MUST be copied from DHCPRELEASEBYRELAY
o Relay Agent Information Option 82 - if present, MUST be copied
from DHCPRELEASEBYRELAY
o Status Code - MAY include the option depending upon the result
DHCPRELAYREPLY MUST be sent as unicast message to the address of the
relay as recorded in DHCPRELEASEBYRELAY.
5. Security Considerations
DHCP protocol as defined in [RFC2131] provides no authentication or
security mechanisms. Potential exposure to attacks are discussed in
Section 7 of the DHCP protocol specification in [RFC2131].
Unauthorized and malicious network device MAY spoof and send the
false DHCPRELEASE message. Similarly unauthorized and malicious
network device MAY spoof and send the false DHCPRELEASEBYRELAY
message.
A defense using the authentication for DHCP messages [RFC3118] SHOULD
be deployed where the networks are not secure or not directly under
the control of the server administrator. The DHCPRELEASEBYRELAY and
DHCPRELAYREPLY messages SHOULD be authenticated using the procedures
described in [RFC3118]. However, implementation of authentication is
not a MUST to support DHCPRELEASEBYRELAY and DHCPRELAYREPLY messages.
Although DHCP network devices that send the DHCPRELEASEBYRELAY
message perform the functions of a DHCP relay, essentially they are
DHCP clients for the purposes of the DHCPRELEASEBYRELAY message.
Thus, [RFC3118] is an appropriate mechanism for DHCPRELEASEBYRELAY
message authentication.
Since [RFC3118] discusses the normal DHCP client interaction,
consisting of a DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, and DHCPACK, it
is necessary to transpose the operations described in [RFC3118] to
the DHCPRELEASEBYRELAY domain. The operations described in [RFC3118]
for DHCPDISCOVER are performed for DHCPRELEASEBYRELAY, and the
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operations described for DHCPOFFER are performed for DHCPRELAYREPLY
message.
6. IANA Considerations
We request IANA to assign following new message types from the
registry of Message Types 53 Values maintained in:
http://www.iana.org/assignments/bootp-dhcp-parameters/
o DHCPRELEASEBYRELAY
o DHCPRELAYREPLY
We request IANA to assign following new Status Code values from the
registry of Status Codes Type 151 Values maintained in:
http://www.iana.org/assignments/bootp-dhcp-parameters/
o NoBinding
o NotConfigured
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>.
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8.2. Informative References
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<http://www.rfc-editor.org/info/rfc2131>.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
<http://www.rfc-editor.org/info/rfc2132>.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, DOI 10.17487/RFC3046, January 2001,
<http://www.rfc-editor.org/info/rfc3046>.
[RFC3118] Droms, R. and W. Arbaugh., Ed., "Authentication for DHCP
Messages", RFC 3118, DOI 10.17487/RFC3118, June 2001,
<http://www.rfc-editor.org/info/rfc3118>.
[RFC6926] Kinnear, K., Stapp, M., Desetti, R., Joshi, B., Russell,
N., Kurapati, P., and B. Volz, "DHCPv4 Bulk Leasequery",
RFC 6926, DOI 10.17487/RFC6926, April 2013,
<http://www.rfc-editor.org/info/rfc6926>.
Author's Address
Sunil M. Gandhewar
Juniper Networks, Inc.
Email: sgandhewar@juniper.net
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