DNS Operations Root Server System Advisory Committee Internet-Draft Intended status: Informational Expires: 2012 July 24 06 February 2012 Replaces RFCs 2010, 2870 Root Name Server Operational Requirements draft-rssac-dnsop-rfc2870bis-04 Status of this Memo 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 July 24, 2012. 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"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." Abstract As the Internet has become critical to the world's social and economic infrastructure, attention has focused on the correct, safe, reliable, and secure operation of the Internet infrastructure itself. The DNS is considered a crucial part of that technical infrastructure. The root domain and its authoritative name servers are a part of that technical infrastructure. The primary focus of this document is to provide guidelines for secure, stable, and resilient authoritative name service for the root zone. Additionally it will look into some specifics for the operation of the name servers. Other operators of authoritative name servers such as those for generic top-level domains (gTLDs), country code top-level domains (ccTLDs) and other zones may also find this document useful. 1. Background The resolution of domain names on the Internet is critically dependent on the proper, safe and secure operation of the root domain name servers. The Internet Assigned Numbers Authority functions operator (IANA) publishes the "root hints" file [HINTS] which lists the names and IP addresses of the thirteen authoritative root name servers that are the focus of this document. This document uses the term "server" to refer to the many ways a root operator provisions to provide root name service, irrespective of physical platform, IP address family or number of concurrent processes. This document provides guidelines for the operation of these root name servers to enable robust and resilient DNS service for the root zone. The root zone service is provided by the root servers operating under the following general characteristics. It is expected that current practice will continue to evolve and we expect future revisions to this work. 1.1 The Internet Corporation for Names and Numbers (ICANN) has appointed a Root Server System Advisory Committee (RSSAC) (http://www.icann.org/committees/dns-root/) to give technical and operational advice to the ICANN board. ICANN and RSSAC expect to use engineering standards developed within the IETF. 1.2 The root servers serve the root (".") and ROOT-SERVERS.NET zones. For legacy reasons, some of the root servers have also served other important zones. In the future, the data served by root servers may change after careful review by RSSAC and ICANN. 1.3 The root servers are neither involved with nor dependent upon any WHOIS [5] data. 1.4 The domain name system has proven to be sufficiently robust that the temporary simultaneous loss of a number of the root server instances has not significantly affect secure and stable operation of the Internet. 1.5 Experience has shown that the Internet is quite vulnerable to incorrect data in the root zone or top-level domain (TLD) zones. Authentication, validation, and security of these data and the communications channels they transit are to be considered possible vulnerabilities. The root server operators have taken steps to harden the communications channels these data transit. [TSIG-7] 1.6 Many of the root operators provision more than one physical or logical host to provide root name service. [ROOTSERVERS] In such configurations, incoming DNS queries to the IP address providing root name service are distributed to multiple hosts using a variety of architectural techniques, including layer-three load balancing devices, equal-cost multipath routing and Anycast routing. (Anycast is discussed further in Section 4.) Since this document is not normative, the key word "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document MAY be interpreted as described in RFC 2119 [1]. 2. The Servers Themselves The following are current practice for the technical details of the root servers themselves: 2.1 Maintaining overall robustness and resilience of the root server system is accomplished by the root server operators by coordinating a heterogeneity of hardware, operating systems, topology, or name serving software across all of the root name server nodes. [ROOTSERVERS] 2.2 Each server runs software which correctly implements the IETF standards for the DNS, currently RFC1035 [2], RFC2181 [3] and RFC4035[14]. While there are no accepted, formal test suites for standards compliance, the maintainers of software used on root servers are expected to take all reasonable actions to conform to the IETF's then-current documented expectations. 2.3 At any time, each server should be able to handle a load of requests for root data which is at least ten times the measured average number of requests on that server in then-current normal conditions. This capacity is usually expressed in queries per second. This specification is intended to ensure continued operation of root services in the event of extreme scenarios, such as distributed denial-of-service (DDoS) attacks and other operational anomalies. 2.4 Each root server should have sufficient connectivity to the Internet to support the bandwidth needs of the above specification. Connectivity to the Internet should be as diverse as possible. While reasonable efforts to ensure that the service is available Internet-wide, events do occur which prevent some nodes from receiving the Root DNS service. These events are out of scope of this document. They may include ISP or end-site misconfiguration, route hi-jacking, routing system problems, DNS redirection or blocking, and congestion in the intermediate ISPs. This is not an exaustive list. 2.5 Servers must provide authoritative responses only from the zones they serve. The servers must disable recursive lookup, forwarding or any other function that might allow them to provide cached answers. For root servers, there IS no place to recurse to and they get no answers from other servers to cache. The response packets should have reasonable IP TTL/IPv6 Hop-Limit values. 64 is current suggested value. The value may be modified by future events. 2.6 Root servers must answer queries from any Internet host, i.e. root servers may not block root name resolution from any valid IP address regardless of address family, except in the case of queries causing operational problems, in which case the blocking should last only as long as the problem, and be as specific as reasonably possible. Root servers must answer queries from the same address family as the query. Root servers may filter any Dynamic Update requests [RFC2136]. They must not accept requested changes unless sent from an authorized sources with appropriate authentication [RFC3007]. 2.7 Root servers may choose to disallow AXFR, or other zone transfer, queries from clients other than other root servers. This restriction is intended to prevent unnecessary load on the root servers. Operators may choose to rate limit traffic bases on protocol. 2.8 Servers must generate checksums when sending UDP datagrams and must verify checksums when receiving UDP datagrams containing a non-zero checksum. 3. Security Considerations The servers need both physical and protocol security as well as unambiguous authentication of their responses. Physical security focuses on the machines and their locations, Protocol security and response authentication are covered by Internet Protocol standards. 3.1. Physical Security Physical security will be commensurate to a level expected of data centers housing mission critical services. Given the global distribution of hardware platforms, these levels may vary. 3.1.1 Whether or not the overall site in which a root server instance is located has access control, the specific area in which the root server is located must have positive access control. At a minimum control measures should be either mechanical or electronic locks. Physical security may be enhanced by the use of intrusion detection and motion sensors, multiple serial access points, security personnel, etc. 3.1.2 Power continuity for at least 24 hours should be assured, whether through on-site batteries, on-site power generation or some combination thereof. There must be procedures that ensure the power fallback mechanisms and supplies are tested no less frequently than the specifications and recommendations of the manufacturer. 3.1.3 Fire detection and/or retardation must be provided. 3.1.4 Provision must be made for rapid return to operation after a system outage. Such provision should involve backup of system software and configuration but may also involve backup hardware which is pre-configured and ready to take over operation, which may require manual procedures. 3.2. Network Security Network security should be of the level provided for critical infrastructure of a major commercial enterprise. 3.2.1 The root servers should not provide services other than DNS name service, secure shell for management, and network time for TSIG and DNSSEC synchronization, e.g. protocols such as HTTP, Telnet, rlogin, FTP, routing daemons, etc. The rational for this argument is that the fewer services running, the less likely there will be interference from non-DNS related events. The only login accounts permitted should be for the server administrator(s). Servers should have a secure mechanism for remote administrative access and maintenance. Failures happen; there will be times when something breaks badly enough that administrators will need to connect remotely. Remote logins should be protected by a secure means that is strongly authenticated and encrypted, and locations from which remote login is allowed should be protected and hardened. Remote logins should be restricted to a list of discrete IP addresses or address ranges. 3.2.2 Root name servers should not trust other hosts, except servers presenting validated credentials, for matters of network time, authentication, encryption keys, or other access or security information. If a root operator uses Kerberos authentication to manage access to the root server, then the associated Kerberos key server must be protected with the same prudence as the root server itself. This applies to all related services which are trusted in any manner. 3.2.3 The broadcast domain on which a root server node is located should not also have other Internet-reachable hosts. Secure monitoring hosts that passively monitor network traffic to and from the root server may be placed in the same broadcast domain. Broadcast domains should be switched or routed so there is less possibility of masquerading. 3.2.4 The broadcast domain(s) in which a root server node is located should be separately firewalled or packet filtered to prohibit network access to any port other than those needed for name service and administration. State-based firewalls for filters should be avoided as they create a DoS point in DNS resolution. 3.2.5 The root servers should have their clocks synchronized via NTP [6], SNTP [7] or similar mechanisms, in as secure manner as possible. For this purpose, servers and their associated firewalls should allow the root servers to be NTP clients. Root servers must not act as NTP peers or servers. 3.2.6 All attempts at intrusion or other compromise should be logged, and all such logs from all root servers may be analyzed by a cooperative security team communicating with all server operators to look for patterns, serious attempts, etc. Logs must available in UTC to facilitate log comparison. 3.2.7 Server logging may be to separate hosts which should be protected similarly to the root servers themselves. 3.2.8 The server should be protected from attacks based on source routing. The server must not solely rely on address- or name-based authentication. 3.2.9 The network on which the server is located should have accurate reverse maps in both in-addr.arpa and ip6.arpa. This is to ensure a valid PTR is returned for the root name servers. 3.3. Protocol Authentication and Security Protocol authentication and security should be to ensure that data presented by the root servers are those created by those authorized to maintain the root zone data. 3.3.1 The root zone should be signed and maintained by the US Depoartment of Commerce contractor in accordance with current DNSSEC specifications ([8], [9] and [10]) and practice. 3.3.2 The root servers must be DNSSEC-capable so that queries may be authenticated by clients with security and authentication concerns. 3.3.3 Transfer of the root zone between root servers must be authenticated and be as secure as reasonably possible. Out of band security validation of updates should be supported. Root server operators have agreed to use TSIG [4] to authenticate root zone distribution from authorized sources. 3.3.4 A "distribution" server, which only allows access by the authorized secondary root servers, may be used. 3.3.5 Root zone updates should only progress after one or more heuristic checks designed to detect erroneous updates have been passed. In case the update fails the tests, human intervention must be requested and the last known good zone published. This is to mitigate the rare but occasional error root zone generation / transmission. 3.3.6 Root zone updates should normally be effective no later than one fourth of the time between root zone updates from notification of the root server operator, based on the current update cycle of a scheduled update every 12 hours. 3.3.7 A special procedure for emergency updates of the root zone should be defined by either the root server operators and/or RSSAC. Updates initiated by the emergency procedure should be made no later than 12 hours after notification. 3.3.8 In the event of a critical network failure, each root server must have a method to update the root zone data via a medium which is delivered through an alternative, non-network, path. In the event that the root server cannot serve current data, it must cease offering DNS service. See also Paragraph 4.3. 3.3.9 Each root should keep global statistics on the amount and types of queries received/answered on a daily basis. These statistics may be made available to RSSAC and RSSAC- sponsored researchers to help determine how to better deploy these machines more efficiently across the Internet. Each root may collect data snapshots to help determine data points such as DNS query storms, significant implementation bugs, etc. This would be a first step in developing a consistent data collection profile for the root zone. 3.3.10 Each root operator must monitor its server to detect operational problems, such as a host being down, a host not running a name server, a name server not returning authoritative answers for the root zone, etc. Servers may also be monitored from an external network. These monitoring processes could be automated. If problems are detected, the appropriate staff should be notified to troubleshoot and remedy the problem. 4. Anycast and Network Considerations The root zone has been available via shared unicast as described in RFC 3258 [11] from several of the authoritative root name servers since 2002. This technique is now commonly referred to as "anycast", despite its differences from the definition of that term in RFC 4786 [12]. Anycast has proven to be a successful method for increasing the capacity and geographic distribution of the root server system. For a root server to offer service successfully using anycast, several current practices should be followed. 4.1 A root server should be anycast using IPv4 address space that is a /24 from pre-RIR allocations. Using any prefix longer than a /20 that is not from the this range risks reachability problems because of filtering by ISPs who won't route such address space. IPv6 address space should be at least a /48. Root server nodes be numbered (v4 and v6) using addresses covered by routes that have been tested and are believed to propagate globally. 4.2 Each of a root server's anycast instances may be sourced from a consistent origin autonomous system (AS). That is, the BGP routing announcement for all instances of a given root server's service address (i.e., the IPv4 address corresponding to the RDATA of that root name server's NS record) should have the same origin AS. 4.3 Each anycast instance of a root server must withdraw its BGP routing announcement upon service failure. Each anycast instance must monitor its ability to provide root name service and withdraw its route if it detects itself unable to provide service. Such monitoring may be automatic and not dependent on a human noticing a service failure. 4.4 Anycast instances using BGP should not use the BGP MULTI_EXIT_DISC (MED) attribute because of possible inter-domain routing (IDR) oscillation in networks using route reflectors or AS confederations. Suggested better alternatives are BGP origin code, altering AS path length (i.e., prepending), adjusting local preference and communities. Specific route oscillation scenarios and mitigations are described in detail in RFC 3345 [13]. 4.5 Some root operators provision different kinds of anycast instances for a given root server. Some instances are designated to be local to particular autonomous systems and thus advertise their routes with the BGP no-export community attribute. Other instances are designated "global" and reachable from anywhere on the Internet; these instances do not advertise with no-export. In the event of this configuration, the local and global instances should not advertise routes with the same prefix length. The global instances should advertise a shorter covering prefix. Failure to advertise a shorter covering prefix from the global instances can result in unreachability in certain scenarios. For example, consider AS A with a local root server anycast instance (i.e., advertising its route with the no-export attribute) announced as prefix P1. AS A prefers its local route to P1 over the other paths to P1 it may have received (corresponding to any global nodes). Now consider AS B that peers only with AS A. Since the local instance of prefix P1 is the best path and is marked no-export, AS A does not send this prefix to AS B. AS B thus has no route to prefix P1 and cannot reach any instances of this root server. Instead, consider if the root server operator advertised a shorter covering prefix P2 for its global instances. In the scenario above, AS A would send prefix P2 to AS B, making any of this root server's global instances reachable from AS B. For IPv4, if the root server prefix is a globally routable /24, and the operator does not have the necessary adjacent address space to aggregate and advertise a shorter prefix, the /24 itself should be advertised globally and a longer prefix (i.e., /25 or longer) designated local-only. Such a longer local-only prefix will not typically be passed across peering boundaries, which eliminates the need to tag this prefix as no-export. 4.6 Root server nodes should be deployed with the highest "splay" possible from other root server nodes. Such deployments will ensure the highest level of service since there will be less fate sharing due to common topology failures, power grid shutdowns, seismic events or other localized disruptions. RFC 1281 describe failures due to fate sharing. Root server operators monitor performance of their service from many locations, and take appropriate steps to maximize their service availability. 5. Communications Communications and coordination between root server operators and between the operators and IANA and ICANN are necessary. 5.1 Planned outages and other scheduled maintenance times should be coordinated between root server operators to ensure that a significant number of the root servers are not all unavailable at the same time. Announcement of planned outages also keeps other operators from investigated a scheduled maintenance window. 5.2 Root server operators may exchange log files, particularly as they relate to security, loading, and other significant events. This may be through a central log coordination point, or may be informal. 5.3 Statistics as they concern usage rates, loading, and resource utilization may be exchanged between operators, and may be reported to IANA for planning and reporting purposes. 5.4 Root name server administrative personnel must be available to provide service 24 hours a day, 7 days per week. On call personnel may be used to provide this service outside of normal working hours. 6. IANA considerations There are no new IANA considerations introduced by this memo. 7. Internationalization considerations There are no new internationalization considerations introduced by this memo. 8. Acknowledgements This work originated with the original root server requirements document and has been substantially updated and revised. Thanks to Bill Manning, Paul Vixie, Mark Kosters and Matt Larson for much of the text and RSSAC for its review. Specific comments were received from Howard Kash, Jim Cassells, Akira Kato, Shinta Sato, Dave Swager, Terry Manderson, David Conrad, Warren Kumari, Ed Lewis, and John Dickinson. 9. References 9.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [3] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, July 1997. [4] Vixie, P., Gudmundsson, O., Eastlake, D., and B. Wellington, "Secret Key Transaction Authentication for DNS (TSIG)", RFC 2845, May 2000. 9.2. Informative References [5] Daigle, L., "WHOIS Protocol Specification", RFC 3912, September 2004. [6] Mills, D., "Network Time Protocol (Version 3) Specification, Implementation", RFC 1305, March 1992. [7] Mills, D., "Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI", RFC 4330, January 2006. [8] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005. [9] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, March 2005. [10] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, March 2005. [11] Hardie, T., "Distributing Authoritative Name Servers via Shared Unicast Addresses", RFC 3258, April 2002. [12] Partridge, C., Mendez, T., and W. Milliken, "Host Anycasting Service", RFC 1546, November 1993. [13] McPherson, D., Gill, V., Walton, D., and A. Retana, "Border Gateway Protocol (BGP) Persistent Route Oscillation Condition", RFC 3345, August 2002. [14] R. Arends, R. Austein, M. Larson, D. Massey, S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, March 2005 [HINTS] Root Hints authoritative source: http://www.internic.net/zones/named.root checked 20120125 Authors' Addresses Root Server System Advisory Committee (RSSAC) Bill Manning, Editor PO Box 12317 Marina del Rey, CA 90295 USA