Internet Draft J. Jeong ETRI/University of Minnesota S. Park SAMSUNG Electronics L. Beloeil France Telecom R&D S. Madanapalli SAMSUNG ISO Expires: April 2005 23 October 2004 IPv6 DNS Configuration based on Router Advertisement draft-jeong-dnsop-ipv6-dns-discovery-03.txt Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which we become aware will be disclosed, in accordance with RFC3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 22, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract Jeong, et al. Expires - April 2005 [Page 1] Internet-Draft IPv6 DNS Configuration based on RA October 2004 This document specifies the steps an IPv6 host takes in deciding how to configure the addresses of recursive DNS servers for DNS name resolution. The way of discovering recursive DNS servers is based on Router Advertisement message. Conventions used in this document 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 [3]. Table of Contents 1. Introduction....................................................2 2. Terminology.....................................................3 3. Overview........................................................3 4. Neighbor Discovery Extension....................................4 4.1. Recursive DNS Server Option................................4 5. Procedure of DNS Configuration..................................5 6. Configuration of DNS Information................................6 6.1. DNS Server Cache Management................................6 6.2. Synchronization between DNS Server Cache and Resolver File.7 6.3. DNS Resolution.............................................8 6.4. Implementation Considerations..............................8 7. Applicability Statements........................................8 8. Open Issues.....................................................9 9. Security Considerations.........................................9 10. Changes from Previous Version of the Draft.....................9 11. Acknowledgements..............................................10 12. Normative References..........................................10 13. Informative References........................................10 14. Authors' Addresses............................................11 15. Intellectual Property Statement...............................12 Full Copyright Statement..........................................12 Acknowledgement...................................................13 1. Introduction Neighbor Discovery (ND) for IP Version 6 and IPv6 Stateless Address Autoconfiguration provide ways to configure either fixed or mobile nodes with one or more IPv6 addresses, default routes and some other parameters [4][5]. 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. Because IPv6 address is too long to remember, some ways to configure IPv6 recursive DNS servers are required for the sake of user's convenience [9]. Jeong, et al. Expires - April 2005 [Page 2] Internet-Draft IPv6 DNS Configuration based on RA October 2004 This document defines the process of DNS configuration based on IPv6 Router Advertisement (RA) to find out the addresses of recursive DNS servers within the local network. 2. Terminology This document uses the terminology described in [4][5]. In addition, three new terms are defined below: Recursive DNS Server (RDNSS) A Recursive DNS Server is a name server that offers the recursive service of DNS name resolution. DNS Server Cache DNS Server Cache is a data structure for managing DNS Server Information existing in IPv6 protocol stack in addition to Neighbor Cache and Destination Cache for Neighbor Discovery [4]. Resolver File Resolver File is a configuration file which DNS resolver on the host uses for DNS name resolution, e.g., /etc/resolv.conf in UNIX. 3. Overview RA approach for RDNSS is to define a new ND option called RDNSS option that contains a recursive DNS server address. Existing ND transport mechanisms (i.e., advertisements and solicitations) are used. This works in the same way that nodes learn about routers and prefixes. An IPv6 host can configure the IPv6 addresses of one or more RDNSSes via RA message periodically sent by router or solicited by a Router Solicitation (RS). This approach needs RDNSS information to be configured in the routers doing the advertisements. The configuration of RDNSS address can be performed manually by operator or other ways, such as automatic configuration through DHCPv6 client running on the router [6]-[8]. When advertising more than one RDNSS option, an RA message includes as many RDNSS options as RDNSSes. Through ND protocol and RDNSS option along with prefix information option, an IPv6 host can perform its network configuration of its IPv6 address and RDNSS simultaneously [4][5]. The RA option for RDNSS can be used on any network that supports the use of ND. Jeong, et al. Expires - April 2005 [Page 3] Internet-Draft IPv6 DNS Configuration based on RA October 2004 However, it is worth noting that some link layers (e.g., WLAN) need to acknowledge multicast packets, which may increase the amount of link-layer traffic [9]. The RA approach is useful in some mobile environments where the addresses of the RDNSSes are changing because the RA option includes a lifetime field that allows client to use RDNSSes nearer to the client. This can be configured to a value that will require the client to time out the entry and switch over to another RDNSS address (see Section 6.1 and 6.2). The preference value of RDNSS, included in RDNSS option, allows IPv6 hosts to select a primary RDNSS among several RDNSSes; this can be used for load balancing of RDNSSes (see Section 6.1 and 6.2). 4. Neighbor Discovery Extension The IPv6 DNS configuration mechanism in this document needs a new ND option in Neighbor Discovery, Recursive DNS Server (RDNSS) option. 4.1. Recursive DNS Server Option RDNSS option contains the IPv6 address of the recursive DNS server. When advertising more than one RDNSS option, an RA message includes as many RDNSS options as DNS servers. Figure 1 shows the format of 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 | Pref | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : IPv6 Address of RDNSS : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. Recursive DNS Server (RDNSS) Option Format Fields: Type 8-bit identifier of the option type (TBD: IANA) Option Name Type Jeong, et al. Expires - April 2005 [Page 4] Internet-Draft IPv6 DNS Configuration based on RA October 2004 RDNSS option (TBD) Length 8-bit unsigned integer. The length of the option (including the type and length fields) in units of 8 octets SHOULD be 0x03 (3 x 8 = 24 octets). Pref The preference of an RDNSS. A 4-bit unsigned integer. A decimal value of 15 indicates the highest preference. A value of zero means unspecified. The field can be used for load balancing of DNS queries with multiple RDNSSes according to local policy. Lifetime 32-bit unsigned integer. The maximum time, in seconds, over which this RDNSS is used for name resolution. Hosts should contact the source of this information, router, before this time interval expires. A value of all one bits (0xffffffff) represents infinity. A value of zero means that the RDNSS must no longer be used. IPv6 Address of RDNSS 128-bit IPv6 address of the recursive DNS server. 5. Procedure of DNS Configuration The processing of RDNSS option is handled like any other ND option and would happen when an RA is received. No new procedure is needed. Figure 2 shows the procedure of DNS configuration for IPv6 host on the basis of IPv6 RA message. IPv6 Host Router | | (a)|(-------------------------RS------------------------->)| (b)|<-----------------RA w/ RDNSS option(s)----------------| (c)| Processing of RA | (d)| Stateless Address Autoconfiguration | (e)| DNS Configuration based on RA option | (f)| (DNS Configuration based on DHCP option) | Figure 2. Procedure of IPv6 Host DNS Configuration The procedure consists of the following steps: Step (a) : IPv6 Host sends RS (Router Solicitation) message to get an RA message. It is optional. Jeong, et al. Expires - April 2005 [Page 5] Internet-Draft IPv6 DNS Configuration based on RA October 2004 Step (b) : For the RS message sent by IPv6 Host, Router sends an RA message, which contains Prefix Information option for stateless address autoconfiguration and RDNSS options for DNS servers. Step (c) : If there are not any Prefix Information option and RDNSS in RA message, IPv6 Host goes to Step (f). Step (d) : If there is Prefix Information option in RA message, IPv6 Host performs stateless address autoconfiguration on the basis of the prefix included in the option. If the stateless autoconfiguration fails, IPv6 Host goes to Step (f). Step (e) : If there is an RDNSS option in RA message, IPv6 Host stores the RDNSS address in both its DNS Server Cache and resolver configuration file. Step (f) : If M (Managed address configuration) flag is set on, IPv6 Host MUST perform stateful address autoconfiguration through DHCPv6 [4]-[6]. If no RDNSS option is included in the RA message, IPv6 Host MAY perform DNS configuration through DHCPv6 [6]-[8] regardless of whether the O flag is set or not. 6. Configuration of DNS Information The RDNSS addresses are announced by RDNSS options in RA message. The newly discovered RDNSS addresses are stored and managed in both DNS Server Cache and Resolver File. 6.1. DNS Server Cache Management The DNS configuration in this document needs a new DNS Server Cache in IPv6 protocol stack in addition to Neighbor Cache and Destination Cache for Neighbor Discovery [4]. Each entry of DNS Server Cache consists of RDNSS address, Preference, Expire-time, and Onsite-flag as follows: - RDNSS address: RDNSS address indicates the recursive DNS server in the site. - Preference: Preference, delivered in RDNSS option, is used for an IPv6 host to decide which RDNSS it will use as a primary RDNSS among the announced RDNSSes. This field can be used for load balancing of DNS queries with multiple RDNSSes within an autonomous site. Jeong, et al. Expires - April 2005 [Page 6] Internet-Draft IPv6 DNS Configuration based on RA October 2004 - Expire-time: Lifetime, delivered in RDNSS option, is used to give the time when this entry becomes invalid. Expire-time is set to the value of Lifetime field of RDNSS option plus the current system time. Whenever a new RDNSS option with the same address is received, this field is updated to have a new expiration time. - Onsite-flag: Onsite-flag is set on while Expire-time is less than the current system time; in other words, while this entry is valid. When Expire-time becomes greater than the current system time, this flag is set off. When Expire-time becomes less than the current system time again through the receipt of another RDNSS option, the flag is set on. The entry of which Onsite-flag is off is not deleted immediately, but used for DNS resolution in the site where the IPv6 host is a mobile node and no RDNSS is provided. Therefore, the IPv6 host MAY use the RDNSS of the previous site even though the RDNSS is in the remote network. To limit the storage needed for the DNS Server Cache, a node MAY need to garbage-collect old entries. However, care must be taken to insure that sufficient space is always present to hold the working set of active entries. Any LRU-based policy that only reclaims entries that have expired should be adequate for garbage- collecting unused entries [4]. For example, when the replacement is necessary, the IPv6 host can choose one of which Onsite-flag is off and of which Expire-time is the least. 6.2. Synchronization between DNS Server Cache and Resolver File When an IPv6 host receives the information of multiple RDNSSes within a site through an RA message with RDNSS options, it stores the RDNSS addresses in order into both DNS Server Cache and Resolver File. The processing of the RDNSS option included in RA message is as follows: Step (a) : Receive and parse RDNSS options. Step (b) : Arrange the addresses of RDNSSes in a descending order, starting with the biggest value of "Pref" field of the RDNSS option and store them in both DNS Server Cache and Resolver File. In the case where there are several routers advertising RDNSS option(s) in a subnet, "Pref" field is used to arrange the information. Step (c) : For each RDNSS option, check the following: If each value of "Pref" and "Lifetime" fields is set to zero, delete the corresponding RDNSS entry from both DNS Server Cache and Resolver File in order to let the RDNSS be not used any more for certain reason in network management, e.g., the Jeong, et al. Expires - April 2005 [Page 7] Internet-Draft IPv6 DNS Configuration based on RA October 2004 breakdown of the RDNSS and a renumbering situation. Step (d) : Delete each entry of which Onsite-flag is set off from DNS Server Cache and the RDNSS address corresponding to the entry from Resolver File. However, in mobile environment, in order that a mobile node can still use the RDNSS of the previous site when the node moves into another site and no RDNSS is available there, it MAY be allowed to maintain the entry of which Onsite-flag is off in both DNS Server Cache and Resolver File. In this case, invalid entries can be deleted according to LRU-based policy. As a last resort of DNS name resolution, an IPv6 host can use the RDNSSes manually configured by its user in its Resolver File either when it cannot get the information of RDNSSes from local network or when there is no valid RDNSS address in DNS Server Cache. 6.3. DNS Resolution Whenever DNS resolver has to resolve a DNS name which is not cached in its local DNS cache, it can use one of the RDNSSes listed in Resolver File, which is synchronized with DNS Server Cache. It refers to RDNSS in order from the first RDNSS among the RDNSSes in Resolver File. 6.4. Implementation Considerations The current ND framework should be modified due to the synchronization between DNS Server Cache for RDNSSes in kernel space and Resolver File in user space. Because it is unacceptable to write and rewrite the Resolver file (e.g., resolv.conf) from the kernel, another approach is needed. One simple approach to solve this is to have a daemon around (or a program that is called at the defined intervals) that keeps monitoring the lifetime of RDNSSes all the time. However, such a daemon is not necessary with the current ND framework. 7. Applicability Statements RA-based DNS configuration is useful in the networks where IPv6 address is autoconfigured through IPv6 stateless address autoconfiguration, such as SOHO, home networks, celluar networks (e.g., 3GPP), MIPv6 (especially, HMIPv6), NEMO and MANET connected to the Internet. Especially, the RA approach is useful in some mobile environments where the addresses of the RDNSSes are changing because the RA option includes a lifetime field that allows client to use RDNSSes nearer to the client. This can be configured to a value that Jeong, et al. Expires - April 2005 [Page 8] Internet-Draft IPv6 DNS Configuration based on RA October 2004 will require the client to time out the entry and switch over to another RDNSS in current local network. 8. Open Issues There might be some issues regarding RA-based DNS configuration as follows: o Can the RA approach be used safely in WLAN networks? Because multicast is unreliable in WLAN networks, some RA messages advertised by a router can be lost [9]. o How can we optimize bandwidth on the link, especially the link of cellular networks, such as 3GPP network? o Is the use of "Pref" or "Lifetime" fields useful? o Is it useful to advertise the well-known anycast addresses for RDNSSes through RA message? The well-known anycast addresses can be set in RA configuration and be announced to IPv6 hosts through RDNSS options in order to reduce the configuration effort of users [10]. o How to implement RA-based DNS configuration? 9. Security Considerations The security of RA option for RDNSS is the same as ND protocol security [4]. The RA option does not add any new vulnerability. It should be noted 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. In the result, the 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 NA replies, answer RS or NS requests, etc. All of this can be done independently of implementing ND. Therefore, the RA option for RDNSS does not add to the vulnerability. Security issues regarding the ND protocol have been discussed at IETF SEND (Securing Neighbor Discovery) Working Group [11]. 10. Changes from Previous Version of the Draft This section briefly lists some of the major changes in this draft relative to the previous version of this same draft, Jeong, et al. Expires - April 2005 [Page 9] Internet-Draft IPv6 DNS Configuration based on RA October 2004 draft-jeong-dnsop-ipv6-dns-discovery-02.txt: - The title of the draft is changed from "IPv6 DNS Discovery based on Router Advertisement" to "IPv6 DNS Configuration based on Router Advertisement". - This version included the consideration of the use of RDNSSes configured manually as a last resort of DNS name resolution in Section 6.2. - This version rewrote Applicability section. - This version rewrote Open Issues, including the consideration of the RA approach in WLAN networks. 11. Acknowledgements This draft has greatly benefited from inputs by Robert Hinden, Pekka Savola, and Tim Chown. The authors appreciate their contribution. 12. Normative References [1] S. Bradner, "Intellectual Property Rights in IETF Technology", RFC 3668, February 2004. [2] S. Bradner, "IETF Rights in Contributions", RFC 3667, February 2004. [3] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [4] T. Narten, E. Nordmark and W. Simpson, "Neighbor Discovery for IP version 6 (IPv6)", RFC 2461, December 1998. [5] S. Thomson and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. 13. Informative References [6] R. Droms et al., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [7] R. Droms, "Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6", RFC 3736, April 2004. Jeong, et al. Expires - April 2005 [Page 10] Internet-Draft IPv6 DNS Configuration based on RA October 2004 [8] R. Droms et al., "DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, December 2003. [9] J. Jeong et al., "IPv6 Host Configuration of DNS Server Information Approaches", draft-ietf-dnsop-ipv6-dns-configuration -04.txt, September 2004, Work in Progress. [10] M. Ohta, "Preconfigured DNS Server Addresses", draft-ohta- preconfigured-dns-01.txt, February 2004, Work in Progress. [11] J. Arkko et al., "SEcure Neighbor Discovery (SEND)", draft- ietf-send-ndopt-06.txt, July 2004, Work in Progress. 14. Authors' Addresses Jaehoon Paul Jeong ETRI/University of Minnesota at Twin Cities 117 Pleasant Street SE Minneapolis, MN 55455 USA Phone: +1 651 587 7774 EMail: jjeong@cs.umn.edu Soohong Daniel Park Mobile Platform Laboratory, SAMSUNG Electronics Korea Phone: +82 31 200 3728 EMail: soohong.park@samsung.com Luc Beloeil France Telecom R&D 42, rue des coutures BP 6243 14066 CAEN Cedex 4 France Phone: +33 02 3175 9391 EMail: luc.beloeil@francetelecom.com Syam Madanapalli Network Systems Division, SAMSUNG India Software Operations India Jeong, et al. Expires - April 2005 [Page 11] Internet-Draft IPv6 DNS Configuration based on RA October 2004 Phone: +91 80 555 0555 EMail: syam@samsung.com 15. Intellectual Property Statement The following intellectual property notice is copied from RFC3668, Section 5. The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Full Copyright Statement The following copyright notice is copied from RFC3667, Section 5.4. It describes the applicable copyright for this document. Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Jeong, et al. Expires - April 2005 [Page 12] Internet-Draft IPv6 DNS Configuration based on RA October 2004 Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Jeong, et al. Expires - April 2005 [Page 13]