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
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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)
<rssac@icann.org>
Bill Manning, Editor
PO Box 12317
Marina del Rey, CA 90295
USA