Modification to Default Value of SOL_MAX_RT
draft-droms-dhc-dhcpv6-solmaxrt-update-02

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.

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This Internet-Draft will expire on July 28, 2012.

Copyright Notice

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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

OLD:
   SOL_MAX_RT      120 secs  Max Solicit timeout value

NEW:
   SOL_MAX_RT     3600 secs  Max Solicit 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 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.

     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.


	

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].

4. Updates to RFC 3315

   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.


	

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) a
   SOL_MAX_RT option.


	

RFC 3315 [RFC3315], section 17.2.2:

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. References

Author's Address

Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Update to RFC 3315
• 3. SOL_MAX_RT option
• 4. Updates to RFC 3315
• 5. Security Considerations
• 6. IANA Considerations
• 7. References
• Author's Address