Internet DRAFT - draft-droms-dhc-dhcpv6-maxsolrt-update
draft-droms-dhc-dhcpv6-maxsolrt-update
Network Working Group R. Droms
Internet-Draft Cisco Systems
Intended status: Standards Track November 14, 2011
Expires: May 17, 2012
Modification to Default Value of MAX_SOL_RT
draft-droms-dhc-dhcpv6-maxsolrt-update-00
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.
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Internet-Draft Abbreviated Title November 2011
1. Introduction
Section 5.5 of the DHCPv6 specification [RFC3315] defines the default
value of MAX_SOL_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 RC 3315
This document changes section 5.5 of RFC 3315 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 RFC 3315.
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 MAX_SOL_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. RFC 3315 was
written with the expectation that the 'M' and 'O' flags in NDP
[RFC2461] would control the use of DHCPv6 by hosts. However, the
current definition of the 'M' and 'O' flags in RFC 4861 [RFC4861]
does not explicitly preclude the use of DHCPv6 by a host. Some
devices are specified to initiate DHCPv6 even if RAs are received
with the 'M' and 'O' bits set to 0. In some circumstances, it is
desirable to enable the assignment of IPv6 addresses through DHCPv6
to some nodes on a link but not to others, which cannot be
implemented through the 'M' and 'O' bits.
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Internet-Draft Abbreviated Title November 2011
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. 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 any IPv6 addresses.
The format of the SOL_MAX_RT option is:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAX_SOL_RT value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_MAX_SOL_RT (TBD).
option-len 4.
MAX_SOL_RT value Overriding value for MAX_SOL_RT in seconds.
Figure 1
If the DHCPv6 server declines to assign any addresses to a client in
an IA_NA or IA_TA option, it MAY include a SOL_MAX_RT option in the
appropriate options field along with a Status Code option indicating
NoAddrsAvail.
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.
4. Security Considerations
This document introduces one security considerations beyond those
described in RFC 3315. 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.
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Internet-Draft Abbreviated Title November 2011
5. IANA Considerations
IANA is requested to assign an options code from the "DHCP Option
Codes" Registry for OPTION_MAX_SOL_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 May 17, 2012 [Page 4]
