| Network Working Group | R. Droms |
| Internet-Draft | Cisco Systems |
| Updates: 3315 (if approved) | June 03, 2013 |
| Intended status: Standards Track | |
| Expires: December 05, 2013 |
Modification to Default Value of SOL_MAX_RT
draft-ietf-dhc-dhcpv6-solmaxrt-update-01
This document updates RFC 3315 by redefining the default values for SOL_MAX_RT and INF_MAX_RT, and defining options through which a DHCPv6 server can override the client's default value for SOL_MAX_RT and INF_MAX_RT with a new value.
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 December 05, 2013.
Copyright (c) 2013 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.
Section 5.5 of the DHCPv6 specification [RFC3315] defines the default values of SOL_MAX_RT and INF_MAX_RT to be 120 seconds. In some circumstances, these defaults 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. While no explicit observations of traffic due to INF_MAX_RT have been conducted, this document updates INF_MAX_RT for consistency with SOL_MAX_RT.
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].
OLD:
SOL_MAX_RT 120 secs Max Solicit timeout value
NEW:
SOL_MAX_RT 3600 secs Max Solicit timeout value
OLD:
INF_MAX_RT 120 secs Max Information-request timeout value
NEW:
SOL_MAX_RT 3600 secs Max Information-request timeout value
This document changes section 5.5 of RFC 3315 [RFC3315] as follows:
With this change, a DHCPv6 client that does not receive a satisfactory response will send Solicit or Information-request messages with the same initial frequency and exponential backoff as specified in sections 17.1.2 and 18.1.5 of RFC 3315 [RFC3315]. However, the long term behavior of these DHCPv6 clients will be to send a Solicit or Information-request message every 3600 seconds rather than every 120 seconds, significantly reducing the aggregated traffic at the DHCPv6 server.
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 Section 3. 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.
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
The format of the SOL_MAX_RT option is:
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].
A DHCPv6 server sends the INF_MAX_RT option to a client to override the default value of INF_MAX_RT. The value of INF_MAX_RT in the option replaces the default value defined in Section 3. One use for the INF_MAX_RT option is to set a longer value for INF_MAX_RT, which reduces the Solicit traffic from a client that has not received a response to its Solicit messages.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INF_MAX_RT value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_INF_MAX_RT (TBD).
option-len 4.
INF_MAX_RT value Overriding value for INF_MAX_RT
in seconds.
Figure 2: INF_MAX_RT option format
The format of the INF_MAX_RT option is:
A DHCPv6 client MUST include the INF_MAX_RT option code in an Option Request option [RFC3315] in any message it sends.
The DHCPv6 server MAY include the INF_MAX_RT option in any response it sends to a client that has included the INF_MAX_RT option code in an Option Request option. The INF_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 INF_MAX_RT option, the client MUST set its internal INF_MAX_RT parameter to the value contained in the INF_MAX_RT option. As a result of receiving this option, the DHCPv6 client MUST NOT send any Information-request messages more frequently than allowed by the retransmission mechanism defined in sections 18.1.5 and 14 of RFC 3315 [RFC3315].
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/or an included INF_MAX_RT option and MAY display the associated status message to the user.
Update to RFC 3315 [RFC3315], section 17.1.3:
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) SOL_MAX_RT and/or INF_MAX_RT options.
Update to RFC 3315 [RFC3315], section 17.2.2:
NEW: A client is not expected to listen for a response during the entire period between transmission of Solicit or Information-Request messages.
Add text to the end of section 14, clarifying client behavior while waiting for a response from a server:
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 and INF_MAX_RT parameters to an arbitrarily high value with the SOL_MAX_RT and INF_MAX_RT options. Assuming the client also receives a response from a valid DHCPv6 server, large values for SOL_MAX_RT and INF_MAX_RT will not have any effect.
IANA is requested to assign an option code from the "DHCP Option Codes" Registry for OPTION_SOL_MAX_RT.
| [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. |