Network Working Group J. Jeong, Ed. Request for Comments: 5006 ETRI/University of Minnesota Category: Experimental S. Park SAMSUNG Electronics L. Beloeil France Telecom R&D S. Madanapalli Ordyn Technologies September 2007 IPv6 Router Advertisement Option for DNS Configuration Status of This Memo This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
AbstractThis document specifies a new IPv6 Router Advertisement option to allow IPv6 routers to advertise DNS recursive server addresses to IPv6 hosts. 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Applicability Statements . . . . . . . . . . . . . . . . . 2 1.2. Coexistence of RDNSS Option and DHCP Option . . . . . . . 2 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Neighbor Discovery Extension . . . . . . . . . . . . . . . . . 4 5.1. Recursive DNS Server Option . . . . . . . . . . . . . . . 4 5.2. Procedure of DNS Configuration . . . . . . . . . . . . . . 5 5.2.1. Procedure in IPv6 Host . . . . . . . . . . . . . . . . 5 6. Implementation Considerations . . . . . . . . . . . . . . . . 6 6.1. DNS Server List Management . . . . . . . . . . . . . . . . 6 6.2. Synchronization between DNS Server List and Resolver Repository . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . . 9
2]. To support the access to additional services in the Internet that are identified by a DNS name, such as a web server, the configuration of at least one recursive DNS server is also needed for DNS name resolution. It is infeasible for nomadic hosts, such as laptops, to be configured manually with a DNS resolver each time they connect to a different wireless LAN (WLAN) such as IEEE 802.11 a/b/g -. Normally, DHCP - is used to locate such resolvers. This document provides an alternate, experimental mechanism which uses a new IPv6 Router Advertisement (RA) option to allow IPv6 routers to advertise DNS recursive server addresses to IPv6 hosts. 10]. The advantages and disadvantages of the RA-based approach are discussed in  along with other approaches, such as the DHCP and well-known anycast addresses approaches. 9]. To order the RA and DHCP approaches, the O (Other stateful configuration) flag can be used in the RA message . If no RDNSS option is included in the RA messages, an IPv6 host may perform DNS configuration through DHCPv6 - regardless of whether the O flag is set or not.
1]. 2] and . In addition, four new terms are defined below: o Recursive DNS Server (RDNSS): Server which provides a recursive DNS resolution service for translating domain names into IP addresses as defined in  and . o RDNSS Option: IPv6 RA option to deliver the RDNSS information to IPv6 hosts . o DNS Server List: A data structure for managing DNS Server Information in the IPv6 protocol stack in addition to the Neighbor Cache and Destination Cache for Neighbor Discovery . o Resolver Repository: Configuration repository with RDNSS addresses that a DNS resolver on the host uses for DNS name resolution; for example, the Unix resolver file (i.e., /etc/resolv.conf) and Windows registry. 2] and ), an IPv6 host can perform network configuration of its IPv6 address and RDNSS simultaneously without needing a separate message exchange for the RDNSS information. The RA option for RDNSS can be used on any network that supports the use of ND. This approach requires RDNSS information to be configured in the routers sending the advertisements. The configuration of RDNSS addresses in the routers can be done by manual configuration. The automatic configuration or redistribution of RDNSS information is
possible by running a DHCPv6 client on the router -. The automatic configuration of RDNSS addresses in routers is out of scope for this document. Figure 1 shows the format of the RDNSS option. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : Addresses of IPv6 Recursive DNS Servers : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Recursive DNS Server (RDNSS) Option Format Fields: Type 8-bit identifier of the RDNSS option type as assigned by the IANA: 25 Length 8-bit unsigned integer. The length of the option (including the Type and Length fields) is in units of 8 octets. The minimum value is 3 if one IPv6 address is contained in the option. Every additional RDNSS address increases the length by 2. The Length field is used by the receiver to determine the number of IPv6 addresses in the option.
Lifetime 32-bit unsigned integer. The maximum time, in seconds (relative to the time the packet is sent), over which this RDNSS address MAY be used for name resolution. Hosts MAY send a Router Solicitation to ensure the RDNSS information is fresh before the interval expires. In order to provide fixed hosts with stable DNS service and allow mobile hosts to prefer local RDNSSes to remote RDNSSes, the value of Lifetime should be at least as long as the Maximum RA Interval (MaxRtrAdvInterval) in RFC 4861, and be at most as long as two times MaxRtrAdvInterval; Lifetime SHOULD be bounded as follows: MaxRtrAdvInterval <= Lifetime <= 2*MaxRtrAdvInterval. A value of all one bits (0xffffffff) represents infinity. A value of zero means that the RDNSS address MUST no longer be used. Addresses of IPv6 Recursive DNS Servers One or more 128-bit IPv6 addresses of the recursive DNS servers. The number of addresses is determined by the Length field. That is, the number of addresses is equal to (Length - 1) / 2. 2].
Section 6.1. Otherwise, go to Step (d). Step (d): For each RDNSS address, if it does not exist in the DNS Server List, register the RDNSS address and lifetime with the DNS Server List and then insert the RDNSS address in front of the Resolver Repository. In the case where the data structure for the DNS Server List is full of RDNSS entries, delete from the DNS Server List the entry with the shortest expiration time (i.e., the entry that will expire first). The corresponding RDNSS address is also deleted from the Resolver Repository. In the order in the RDNSS option, position the newly added RDNSS addresses in front of the Resolver Repository so that the new RDNSS addresses may be preferred according to their order in the RDNSS option for the DNS name resolution. The processing of these RDNSS addresses is finished here. Note that, in the case where there are several routers advertising RDNSS option(s) in a subnet, the RDNSSes that have been announced recently are preferred. Step (e): Delete each expired entry from the DNS Server List, and delete the RDNSS address corresponding to the entry from the Resolver Repository.
2]. However, any new vulnerability in this RA option is not known yet. In this context, it can be claimed that the vulnerability of ND is not worse and is a subset of the attacks that any node attached to a LAN can do independently of ND. A malicious node on a LAN can promiscuously receive packets for any router's MAC address and send packets with the router's MAC address as the source MAC address in the L2 header. As a result, L2 switches send packets addressed to the router to the malicious node. Also, this attack can send redirects that tell the hosts to send their traffic somewhere else. The malicious node can send unsolicited RA or Neighbor Advertisement (NA) replies, answer RS or Neighbor Solicitation (NS) requests, etc. Also, an attacker could configure a host to send out an RA with a fraudulent RDNSS address, which is presumably an easier avenue of attack than becoming a rogue router and having to process all traffic for the subnet. It is necessary to disable the RA RDNSS option in both routers and clients administratively to avoid this problem. All of this can be done independently of implementing ND. Therefore, it can be claimed that the RA option for RDNSS has vulnerabilities similar to those existing in current mechanisms. If the Secure Neighbor Discovery (SEND) protocol is used as a security mechanism for ND, all the ND options including the RDNSS option are automatically included in the signatures , so the RDNSS transport is integrity-protected. However, since any valid SEND node can still insert RDNSS options, SEND cannot verify who is or is not authorized to send the options. http://www.iana.org/assignments/icmpv6-parameters
 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007.  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007.  Mockapetris, P., "Domain Names - Concepts and Facilities", RFC 1034, November 1987.  Mockapetris, P., "Domain Names - Implementation and Specification", RFC 1035, November 1987.  Droms, R., Ed., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.  Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6", RFC 3736, April 2004.  Droms, R., Ed., "DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, December 2003.  Jeong, J., Ed., "IPv6 Host Configuration of DNS Server Information Approaches", RFC 4339, February 2006.  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004.  Arkko, J., Ed., "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.  ANSI/IEEE Std 802.11, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", March 1999.  IEEE Std 802.11a, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHZ Band", September 1999.
 IEEE Std 802.11b, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Higher-Speed Physical Layer Extension in the 2.4 GHz Band", September 1999.  IEEE P802.11g/D8.2, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Further Higher Data Rate Extension in the 2.4 GHz Band", April 2003.  Damas, J. and F. Neves, "Preventing Use of Recursive Nameservers in Reflector Attacks", Work in Progress, July 2007.  Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000.
http://www.cs.umn.edu/~jjeong/ Soohong Daniel Park Mobile Convergence Laboratory SAMSUNG Electronics 416 Maetan-3dong, Yeongtong-Gu Suwon, Gyeonggi-Do 443-742 Korea Phone: +82 31 200 4508 EMail: firstname.lastname@example.org Luc Beloeil France Telecom R&D 42, rue des coutures BP 6243 14066 CAEN Cedex 4 France Phone: +33 02 3175 9391 EMail: email@example.com Syam Madanapalli Ordyn Technologies 1st Floor, Creator Building, ITPL Bangalore - 560066 India Phone: +91-80-40383000 EMail: firstname.lastname@example.org
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