Internet Draft Jaehoon Paul Jeong ETRI Soohong Daniel Park SAMSUNG Electronics Luc Beloeil France Telecom R&D Syam Madanapalli SAMSUNG ISO draft-jeong-dnsop-ipv6-dns-discovery-01.txt Expires: August 2004 13 February 2004 IPv6 DNS Discovery based on Router Advertisement Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 except that the right to produce derivative works is not granted [1]. 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. Abstract This document specifies the steps a node takes in deciding how to autoconfigure the address of recursive DNS server for DNS name resolution. The way of discovering recursive DNS server is based on Router Advertisement message. Conventions used in this document Jeong, et al. Expires - August 2004 [Page 1] Internet-Draft IPv6 DNS Discovery based on RA February 2004 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 [2]. Table of Contents 1. Terminology.....................................................2 2. Introduction....................................................2 3. Overview........................................................3 4. Neighbor Discovery Extension....................................3 4.1 DNS Server Option...........................................3 5. Procedure of DNS Discovery......................................4 6. Autoconfiguration of DNS Information............................5 6.1 DNS Server Cache Management.................................5 6.2 Synchronization between DNS Server Cache and Resolver File..6 6.3 DNS Resolution..............................................7 7. Applicability Statements........................................7 8. Open Issues.....................................................7 9. Security Considerations.........................................8 10. Changes from Previous Version of the Draft.....................8 11. Copyright......................................................8 12. Normative References...........................................9 13. Informative References.........................................9 14. Authors' Addresses............................................10 1. Terminology This memo uses the terminology described in [3][4]. 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 [3]. 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. 2. Introduction Jeong, et al. Expires - August 2004 [Page 2] Internet-Draft IPv6 DNS Discovery based on RA February 2004 IPv6 stateless address autoconfiguration provides a way to autoconfigure either fixed or mobile nodes with one or more IPv6 addresses, default routes and some other parameters [3][4]. For the support of the various services in the Internet, such as web service, not only the configuration of IP address for network interface, but also that of at least one recursive DNS server for DNS name resolution is necessary. This document defines the process of DNS discovery based on IPv6 Router Advertisement (RA) to find out the address of recursive DNS server within the local network. 3. Overview An IPv6 host can autoconfigure DNS information via RA message sent periodically by router. Namely, an IPv6 host can autoconfigure the IPv6 address of RDNSS for DNS name resolution through DNS Server option included in RA message. 4. Neighbor Discovery Extension The DNS discovery mechanism in this document needs a new RA option in Neighbor Discovery, DNS Server option. 4.1 DNS Server Option DNS Server option contains the IPv6 address of the recursive DNS server. When advertising more than one DNS Server option, an RA message includes as many DNS Server options as DNS servers. Figure 1 shows the format of DNS Server 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 DNS Server + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Jeong, et al. Expires - August 2004 [Page 3] Internet-Draft IPv6 DNS Discovery based on RA February 2004 Figure 1. DNS Server Option Format Fields: Type 8-bit identifier of the option type (TBD: IANA) Option Name Type DNS Server (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 a DNS server. 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 DNS server is used for name resolution. Hosts should contact the source of this information, router, before expiry of this time interval. A value of all one bits (0xffffffff) represents infinity. A value of zero means that the DNS server must not be used any more. IPv6 Address of DNS Server Recursive DNS Server's address for DNS name resolution. 5. Procedure of DNS Discovery IPv6 Host Router | | (a)|(-------------------------RS------------------------->)| (b)|<------------------RA w/ DNS option(s)-----------------| (c)| Processing of RA | (d)| Stateless Address Autoconfiguration | (e)| Stateless DNS Autoconfiguration | (f)| (Stateful Address or DNS Autoconfiguration) | Figure 2. Procedure of DNS Discovery Jeong, et al. Expires - August 2004 [Page 4] Internet-Draft IPv6 DNS Discovery based on RA February 2004 Figure 2 shows the procedure of DNS Discovery on the basis of IPv6 RA message. The procedure consists of the following steps. Step (a) : IPv6 Host sends RS (Router Solicitation) message to get RA message. It is optional. Step (b) : For the RS message received from IPv6 Host, Router sends RA message, which contains Prefix Information option for stateless address autoconfiguration and DNS Server options for DNS server's addresses. Step (c) : If there are not any Prefix Information option and DNS Server option 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 based on the prefix included in the option. If the auto- configuration fails, IPv6 Host goes to Step (f). Step (e) : If there is DNS Server option in RA message, IPv6 Host stores the DNS server's address in 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 [3-5]. If O (Other stateful configuration) flag is set on, IPv6 Host MAY perform stateful DNS auto- configuration through DHCPv6, too [3-5]. 6. Autoconfiguration of DNS Information The addresses of DNS servers are announced by DNS Server options in RA message. These addresses can be used for recursive DNS service providing DNS name resolution. The newly discovered DNS information, i.e., RDNSS's address, is stored and managed in both DNS Server Cache and Resolver File. 6.1 DNS Server Cache Management DNS Discovery in this document needs a new DNS Server Cache in IPv6 protocol stack in addition to Neighbor Cache and Destination Cache for Neighbor Discovery [3]. Each entry of DNS Server Cache consists of DNS Server's IPv6 address, Preference, Expire-time, and Onsite- flag as follows: - DNS Server's IPv6 address: DNS Server's IPv6 address indicates the recursive DNS server in the site. Jeong, et al. Expires - August 2004 [Page 5] Internet-Draft IPv6 DNS Discovery based on RA February 2004 - Preference: Preference, delivered in DNS Server option, is used to give the usage preference to the announced DNS servers; e.g., the value of two of preference field may indicate a primary DNS server and that of one a secondary one. Like this, this field can be used for load balancing of DNS queries with multiple RDNSSes within a autonomous site. - Expire-time: Lifetime, delivered in DNS Server option, is used to give the time when this entry becomes invalid. Expire-time is set to the value of Lifetime field of DNS Server option plus the current system time. Whenever a new DNS Server option with the same address is received, it is updated. - Onsite-flag: Onsite-flag is set on while Expire-time is less than the current system time, namely this entry is valid. When Expire-time becomes greater than the current system time, this flag is set to off. When Expire-time becomes less than the current system time again through a receipt of another DNS Server 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 IPv6 host is mobile node and recursive DNS server is not provided. In such a site, IPv6 host MAY use the DNS server of the previous site. 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 [3]. For example, when the replacement is necessary, 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 DNS Server options, it stores the RDNSS addresses in order into both DNS Server Cache and Resolver File. The processing of the DNS Server option included in RA message is as follows: Step (a) : Receive and parse DNS Server options. Step (b) : Arrange the addresses of RDNSSes in a descending order, starting with the biggest value of "Pref" field of the DNS Server option and store them in both DNS Server Cache Jeong, et al. Expires - August 2004 [Page 6] Internet-Draft IPv6 DNS Discovery based on RA February 2004 and Resolver File. In the case where there are several routers advertising DNS Server option(s) in a subnet, "Pref" field is used to arrange the information. Step (c) : For each DNS Server option, check the following: If the 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 not used any more for certain reason in network management, e.g., the breakdown of the DNS server and a renumbering situation. Step (d) : Delete each entry of which Onsite-flag is set off from DNS Server Cache and the address of DNS server corresponding to the entry from Resolver File. In mobile environments, in order that a mobile node still uses a DNS server of the previous site when the node moves into another site and no DNS server is available there, it MAY be allowed to maintain the entry of which Onsite-flag is off, not to delete it from both DNS Server Cache and Resolver File. The actual synchronization between the above two storages is performed through a DNS API dependent on operating system. Whenever DNS resolver should resolve a DNS name which is not cached in its local DNS cache, it can use DNS servers listed in Resolver File, which is synchronized with DNS Server Cache. 6.3 DNS Resolution Whenever the resolver on the host performs the name resolution, it refers to the address of RDNSS in order from the first RDNSS stored in Resolver File. 7. Applicability Statements RA-based DNS discovery is efficient in many kinds of wireless networks where IPv6 address is autoconfigured by IPv6 stateless address autoconfiguration, such as SOHO, home network, MIPv6 (especially, HMIPv6), NEMO and MANET connected to the Internet. 8. Open Issues There might be some issues regarding RA-based DNS discovery as follows: o How to optimize bandwidth on the link? o How to implement RA-based DNS discovery? Jeong, et al. Expires - August 2004 [Page 7] Internet-Draft IPv6 DNS Discovery based on RA February 2004 o What about the use of "Pref" or "Lifetime" field? o What about several routers on the same link advertising distinct parameters, such as Prefix Information options and DNS Server options? (Multihoming considerations) o What about advertising DHCPv6 Server's address through RA message as indirect DNS discovery? DHCP-lite or Stateless DHCP can be considered together [6]. 9. Security Considerations This security is essentially related to Neighbor Discovery protocol security [3]. If someone wants to hijack correct RS message, they could send an RA message with incorrect DNS Server options to the host and they would take incorrect RA message through the above mechanism, which is unsafe processing. As described in [3], an IPv6 host can check the validity of NDP messages. If the NDP message includes an IP Authentication Header, the message can be authenticated. Security issues regarding the Neighbor Discovery protocol are being discussed in IETF SEND (Securing Neighbor Discovery) working group [7]. 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, draft-jeong-dnsop-ipv6-dns-discovery-00.txt: - excluded DNS Zone Suffix Option. - introduced DNS Server Cache in order to store the list of DNS Server addresses in part of IPv6 Neighbor Discovery. - clarified the use of M and O flag in RA message to explain the cooperation between Stateless and Stateful Autoconfigurations. 11. Copyright The following copyright notice is copied from RFC 2026 [Bradner, 1996], Section 10.4, and describes the applicable copyright for this document. Copyright (C) The Internet Society July 12, 2001. All Rights Reserved. Jeong, et al. Expires - August 2004 [Page 8] Internet-Draft IPv6 DNS Discovery based on RA February 2004 This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. 12. Normative References [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [3] T. Narten, E. Nordmark and W. Simpson, "Neighbor Discovery for IP version 6 (IPv6)", RFC 2461, December 1998. [4] S. Thomson and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. 13. Informative References [5] R. Droms et al., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [6] R. Droms, "Stateless DHCP Service for IPv6", draft-ietf-dhc- dhcpv6-stateless-04.txt, January 2004. [7] J. Arkko et al., "SEcure Neighbor Discovery (SEND)", draft-ietf- send-ndopt-03.txt, January 2004. Jeong, et al. Expires - August 2004 [Page 9] Internet-Draft IPv6 DNS Discovery based on RA February 2004 14. Authors' Addresses Jaehoon Paul Jeong ETRI / PEC 161 Gajong-Dong, Yusong-Gu Daejon 305-350 Korea Phone: +82-42-860-1664 EMail: paul@etri.re.kr 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 Phone: +91-80-555-0555 EMail: syam@samsung.com Jeong, et al. Expires - August 2004 [Page 10]