Internet DRAFT - draft-droms-dhc-dhcpv6-solmaxrt-update
draft-droms-dhc-dhcpv6-solmaxrt-update
Network Working Group R. Droms
Internet-Draft Cisco Systems
Updates: 3315 (if approved) August 3, 2012
Intended status: Standards Track
Expires: February 4, 2013
Modification to Default Value of SOL_MAX_RT
draft-droms-dhc-dhcpv6-solmaxrt-update-03
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
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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.
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.
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.
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:
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Internet-Draft DHCPv6 SOL_MAX_RT Option August 2012
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 [RFC3315] or IA_PD [RFC3633] option.
If a DHCPv6 client receives a message 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 3315 [RFC3315].
4. Updates to RFC 3315
RFC 3315 [RFC3315], section 17.1.3:
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OLD:
The client MUST ignore any Advertise message that includes a Status
Code option containing the value NoAddrsAvail, with the exception
that the client MAY display the associated status message to the
user.
NEW:
The client MUST ignore any Advertise message that includes a Status
Code option containing the value NoAddrsAvail, with the exception
that the client MUST process an included SOL_MAX_RT option and MAY
display the associated status message to the user.
Figure 2
RFC 3315 [RFC3315], section 17.2.2:
OLD:
If the server will not assign any addresses to any IAs in a
subsequent Request from the client, the server MUST send an
Advertise message to the client that includes only a Status Code
option with code NoAddrsAvail and a status message for the user, a
Server Identifier option with the server's DUID, and a Client
Identifier option with the client's DUID.
NEW:
If the server will not assign any addresses to any IAs in a
subsequent Request from the client, the server MUST send an
Advertise message to the client that includes only a Status Code
option with code NoAddrsAvail and a status message for the user, a
Server Identifier option with the server's DUID, a Client
Identifier option with the client's DUID and (optionally) a
SOL_MAX_RT option.
Figure 3
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5. Security Considerations
This document introduces one security consideration 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.
6. IANA Considerations
IANA is requested to assign an option code from the "DHCP Option
Codes" Registry for OPTION_SOL_MAX_RT.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 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
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