Internet DRAFT - draft-halwasia-dhc-inform-refresh-time-opt
draft-halwasia-dhc-inform-refresh-time-opt
Network Working Group S. Bhandari
Internet-Draft G. Halwasia
Intended status: Standards Track B. Volz
Expires: March 14, 2013 Cisco Systems
September 10, 2012
DHCPv4 INFORM Refresh Time Option
draft-halwasia-dhc-inform-refresh-time-opt-00
Abstract
This document describes a Dynamic Host Configuration Protocol for
IPv4 (DHCPv4) [RFC2131] option for specifying an upper bound for how
long a client should wait before refreshing information retrieved
from DHCPv4 Server by using DHCP INFORM message. It is used with
stateless DHCPv4 as there are no addresses or other entities with
lifetimes that can tell the client when to contact the DHCPv4 server
to refresh its configuration.
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].
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 March 14, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Internet-Draft DHCPv4 INFORM Refresh Time Option September 2012
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. DHCPv4 INFORM Refresh Time Option . . . . . . . . . . . . . . . 3
3. Client Behaviour . . . . . . . . . . . . . . . . . . . . . . . 4
4. Server Behaviour . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
DHCPv4 [RFC2131] specifies DHCP INFORM message which a client can
sent to obtain other local configuration parameters in case client
has obtained a network address through some other means. This other
configuration data will typically have no associated "lease", hence
there may be no information telling a host when to refresh its
configuration data. Therefore, an option that can be used from
server to client to inform the client when it should refresh the
other configuration data is needed.
This option is useful in many situations:-
- Unstable environments where unexpected changes are likely to occur.
- For planned changes, including renumbering. An administrator can
gradually decrease the time as the event nears.
- Use cases described in [I-D.bhandari-netext-pmipv6-dhcp-options]
also intends to use this option to exchange configuration parameters
in between MAG and LMA.
2. DHCPv4 INFORM Refresh Time Option
The INFORM refresh time option specifies an upper bound for how long
a client should wait before refreshing configuration parameters
retrieved from DHCPv4. It is only used in DHCP ACK messages in
response to DHCP INFORM messages. In other messages there will
usually be other options that indicate when the client should contact
the server. Note that it is only an upper bound. If the client has
any reason to send DHCP INFORM before the refresh time expires, it
should attempt to refresh all the configuration parameters. A client
may contact the server before the refresh time expires due to various
reasons. For example, it may need additional configuration
parameters (such as by an application), or that it has an indication
that it may have moved to a new link etc. The expiry of the refresh
time in itself does not in any way mean that the client should remove
the data. The client should keep its current data while attempting
to refresh it. When a client receives a ACK message to an INFORM
message that contains configuration information, it should install
that new configuration information after removing any previously
received configuration information. It should also remove
information that is missing from the new information set, e.g., an
option might be left out or contain only a subset of what it did
previously.
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The format of the DHCPv4 INFORM Refresh Time Option option is shown
below.
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-code | option-len | option-value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-value(cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: 8-bit option code
option-len: 4
option-value: Time duration relative to the current time,
expressed in units of seconds
3. Client Behaviour
A client MUST request this option in the Parameter Request List
Option when sending Parameter Request List message to the DHCPv4
server. A client MUST NOT request this option in the Parameter
Request List option in any other messages. This document recommends
default refresh time of 86400 seconds and minimum default refresh
time of 600 seconds. If the Reply to an INFORM message does not
contain this option, the client MUST behave as if the option with
value 86400 seconds (24 hrs) was provided. A client MUST use the
refresh time of 600 seconds if it receives the option with a value
less than 600 seconds.
The value 0xffffffff in this option implies that the client should
not refresh its configuration data without some other trigger (such
as detecting movement to a new link). If a client contacts the
server to obtain new data or refresh some existing data before the
refresh time expires, then it SHOULD also refresh all data covered by
this option. When the client detects that the refresh time has
expired, it SHOULD try to update its configuration data by sending an
INFORM message as specified in section 4.4.3 of [RFC2131]. A client
MAY have a maximum value for the refresh time, where that value is
used whenever the client receives this option with a value higher
than the maximum. This also means that the maximum value is used
when the received value is "0xffffffff". A maximum value might make
the client less vulnerable to attacks based on forged DHCP messages.
Without a maximum value, a client may be made to use wrong
information for a possibly infinite period of time. There may
however be reasons for having a very long refresh time, so it may be
useful for this maximum value to be configurable.
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4. Server Behaviour
A server sending a ACK message to an INFORM message SHOULD include
this option if it is requested in the Parameter Request List Option
of the INFORM message. The option value MUST NOT be smaller than 600
seconds. The server SHOULD give a warning if it is configured with a
smaller value. The option MUST only appear in the ACK messages.
5. IANA Considerations
This document defines DHCPv4 INFORM Refresh Time Option which
requires assignment of DHCPv4 option code TBD1 assigned from "Bootp
and DHCP options" registry (http://www.iana.org/assignments/ bootp-
dhcp-parameters/bootp-dhcp-parameters.xml), as specified in
[RFC2939].
6. Security Considerations
Section 7 of [RFC2131] outlines the DHCPv4 security considerations.
This option does not change these in any significant way. An
attacker could send faked ACK messages with a low INFORM refresh time
value, which would trigger use of minimum recommended value of 600
seconds to minimize this threat. Another attack might be to send a
very large value, to make the client use forged information for a
long period of time. A possible maximum limit at the client is
suggested, which would reduce this problem.
7. Acknowledgements
Thanks to Authors of [RFC4242] as this document is essentially an
edited version of their memo.
8. Normative References
[I-D.bhandari-netext-pmipv6-dhcp-options]
Systems, C. and S. Kumar, "DHCPv4 Configuration Options in
PMIPv6", draft-bhandari-netext-pmipv6-dhcp-options-00
(work in progress), July 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
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[RFC2939] Droms, R., "Procedures and IANA Guidelines for Definition
of New DHCP Options and Message Types", BCP 43, RFC 2939,
September 2000.
[RFC4242] Venaas, S., Chown, T., and B. Volz, "Information Refresh
Time Option for Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 4242, November 2005.
Authors' Addresses
Shwetha Bhandari
Cisco Systems
Cessna Business Park, Sarjapura Marathalli Outer Ring Road
Bangalore, KARNATAKA 560 087
India
Phone: +91 80 4426 0474
Email: shwethab@cisco.com
Gaurav Halwasia
Cisco Systems
Cessna Business Park, Sarjapura Marathalli Outer Ring Road
Bangalore, KARNATAKA 560 087
India
Phone: +91 80 4426 1321
Email: ghalwasi@cisco.com
Bernie Volz
Cisco Systems
1414 Massachusetts Ave
BOXBOROUGH, MASSACHUSETTS 01719
UNITED STATES
Phone: +1 978 936 0382
Email: volz@cisco.com
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