Network Working Group R. Droms
Internet-Draft Cisco Systems
Intended status: Standards Track December 15, 2011
Expires: June 17, 2012
Modification to Default Value of SOL_MAX_RT
draft-droms-dhc-dhcpv6-solmaxrt-update-01
Abstract
This document updates RFC 3315 by redefining the default value for
SOL_MAX_RT and defining an option through which a DHCPv6 server can
override the client's default value for SOL_MAX_RT with a new value.
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 June 17, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Droms Expires June 17, 2012 [Page 1]
Internet-Draft Abbreviated Title December 2011
1. Introduction
Section 5.5 of the DHCPv6 specification [RFC3315] defines the default
value of SOL_MAX_RT to be 120 seconds. In some circumstances, this
default will lead to an unacceptably high volume of aggregated
traffic at a DHCPv6 server.
1.1. 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].
2. Update to RFC 3315
This document changes section 5.5 of RFC 3315 [RFC3315] as follows:
OLD:
SOL_MAX_RT 120 secs Max Solicit timeout value
NEW:
SOL_MAX_RT 3600 secs Max Solicit timeout value
With this change, a DHCPv6 client that does not receive a
satisfactory response will send Solicit messages with the same
initial frequency and exponential backoff as specified in section
17.1.2 of RFC 3315 [RFC3315]. However, the long term behavior of
these DHCPv6 clients will be to send a Solicit message every 3600
seconds rather than every 120 seconds, significantly reducing the
aggregated traffic at the DHCPv6 server.
The change to SOL_MAX_RT is in response to DHCPv6 message rates
observed at a DHCPv6 server in a deployment in which many DHCPv6
clients are sending Solicit messages but the DHCPv6 server has been
configured not to respond to those Solicit messages.
3. SOL_MAX_RT option
A DHCPv6 server sends the SOL_MAX_RT option to a client to override
the default value of SOL_MAX_RT. The value of SOL_MAX_RT in the
option replaces the default value defined in RFC 3315 [RFC3315]. One
use for the SOL_MAX_RT option is to set a longer value for
SOL_MAX_RT, which reduces the Solicit traffic from a client that has
not received a response to its Solicit messages.
The format of the SOL_MAX_RT option is:
Droms Expires June 17, 2012 [Page 2]
Internet-Draft Abbreviated Title December 2011
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SOL_MAX_RT value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_SOL_MAX_RT (TBD).
option-len 4.
SOL_MAX_RT value Overriding value for SOL_MAX_RT in seconds.
Figure 1
A DHCPv6 client MUST include the SOL_MAX_RT option code in an Option
Request option [RFC3315] in any message it sends.
The DHCPv6 server MAY include the SOL_MAX_RT option in any response
it sends to a client that has included the SOL_MAX_RT option code in
an Option Request option. The SOL_MAX_RT option is sent in the main
body of the message to client, not as a sub-option in, e.g., an
IA_NA, IA_TA or IA_PD option.
If a DHCPv6 client receives an IA_NA or IA_TA option containing a
SOL_MAX_RT option, the client MUST set its internal SOL_MAX_RT
parameter to the value contained in the SOL_MAX_RT option. As a
result of receiving this option, the DHCPv6 client MUST NOT send any
Solicit messages more frequently than allowed by the retransmission
mechanism defined in sections 17.1.2 and 14 of RFC 315 [RFC3315].
4. Security Considerations
This document introduces one security considerations beyond those
described in RFC 3315 [RFC3315]. A malicious DHCPv6 server might
cause a client to set its SOL_MAX_RT parameter to an arbitrarily high
value with the SOL_MAX_RT option. Assuming the client also receives
a response from a valid DHCPv6 server, the large value for SOL_MAX_RT
will not have any effect.
5. IANA Considerations
IANA is requested to assign an option code from the "DHCP Option
Droms Expires June 17, 2012 [Page 3]
Internet-Draft Abbreviated Title December 2011
Codes" Registry for OPTION_SOL_MAX_RT.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[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.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
Author's Address
Ralph Droms
Cisco Systems
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Phone: +1 978 936 1674
Email: rdroms@cisco.com
Droms Expires June 17, 2012 [Page 4]