draft-ietf-dnsop-root-loopback-00.txt   draft-ietf-dnsop-root-loopback-01.txt 
Network Working Group W. Kumari Network Working Group W. Kumari
Internet-Draft Google Internet-Draft Google
Intended status: Informational P. Hoffman Intended status: Informational P. Hoffman
Expires: June 3, 2015 VPN Consortium Expires: July 15, 2015 VPN Consortium
November 30, 2014 January 11, 2015
Decreasing Access Time to Root Servers by Running One on Loopback Decreasing Access Time to Root Servers by Running One on Loopback
draft-ietf-dnsop-root-loopback-00 draft-ietf-dnsop-root-loopback-01
Abstract Abstract
Some DNS recursive resolvers have longer-than-desired round trip Some DNS recursive resolvers have longer-than-desired round trip
times to the closest DNS root server. Such resolvers can greatly times to the closest DNS root server. Some DNS recursive resolver
decrease the round trip time by running a copy of the full root zone operators want to prevent snooping of requests sent to DNS root
on a loopback address (such as 127.0.0.1). Typically, the vast servers by third parties. Such resolvers can greatly decrease the
majority of queries going to the root are for names that do not exist round trip time and prevent observation of requests by running a copy
in the root zone, and the negative answers are cached for a much of the full root zone on a loopback address (such as 127.0.0.1).
shorter period of time. This document shows how to start and This document shows how to start and maintain such a copy of the root
maintain such a copy of the root zone in a manner that is secure for zone that does not pose a threat to other users of the DNS, at the
the operator of the recursive resolver and does not pose a threat to cost of adding some operational fragility for the operator.
other users of the DNS.
Status of This Memo Status of This Memo
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Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Operation of the Root Zone on the Loopback Address . . . . . 4 3. Operation of the Root Zone on the Loopback Address . . . . . 4
4. Using the Root Zone Server on the Loopback Address . . . . . 4 4. Using the Root Zone Server on the Loopback Address . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 5 8.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Current Sources of the Root Zone . . . . . . . . . . 5 Appendix A. Current Sources of the Root Zone . . . . . . . . . . 6
Appendix B. Example Configurations of Common Implementations . . 6 Appendix B. Example Configurations of Common Implementations . . 7
B.1. Example Configuration: BIND 9.9 . . . . . . . . . . . . . 6 B.1. Example Configuration: BIND 9.9 . . . . . . . . . . . . . 7
B.2. Example Configuration: Unbound 1.4 and NSD 4 . . . . . . 7 B.2. Example Configuration: Unbound 1.4 and NSD 4 . . . . . . 8
B.3. Example Configuration: Microsoft Windows Server 2012 . . 8 B.3. Example Configuration: Microsoft Windows Server 2012 . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
DNS recursive resolvers have to answer all queries from their DNS recursive resolvers have to provide answers to all queries from
customers, even those which are for domain names that do not exist. their customers, even those which are for domain names that do not
For each queried name that has a top level domain (TLD) that is not exist. For each queried name that has a top level domain (TLD) that
in the recursive resolver's cache, the resolver must send a query to is not in the recursive resolver's cache, the resolver must send a
a root server to get the information for that TLD, or to find out query to a root server to get the information for that TLD, or to
that the TLD does not exist. If there is a slow path between the find out that the TLD does not exist. Typically, the vast majority
recursive resolver and the closest root server, getting slow of queries going to the root are for names that do not exist in the
responses to these queries has a negative effect on the resolver's root zone, and the negative answers are cached for a much shorter
period of time. A slow path between the recursive resolver and the
closest root server has a negative effect on the resolver's
customers. customers.
Recursive resolvers currently send queries for all TLDs that are not
in their caches to root servers, even though most of those queries
get answers that are referrals to other servers. Malicious third
parties might be able to observe that traffic on the network between
the recursive resolver and one or more of the DNS roots.
This document describes a method for the operator of a recursive This document describes a method for the operator of a recursive
resolver to greatly speed these queries. The basic idea is to create resolver to greatly speed these queries and to hide them from
an up-to-date root zone server on a loopback address on the same host outsiders. The basic idea is to create an up-to-date root zone
as the recursive server, and that server is used when the recursive server on a loopback address on the same host as the recursive
resolver uses for looking up root information. The recursive server, and use that server when the recursive resolver looks up root
resolver validates all responses from the root server on the loopback information. The recursive resolver validates all responses from the
address, just as it would all responses from a remote root server. root server on the loopback address, just as it would all responses
from a remote root server.
The primary goal of this design is to provide faster negative The primary goals of this design is to provide faster negative
responses to stub resolver queries that contain junk queries. This responses to stub resolver queries that contain junk queries, and to
design will probably have little effect on getting faster positive prevent queries and responses from being visible on the network.
responses to stub resolver for good queries on TLDs, because the data This design will probably have little effect on getting faster
for those zones is usually long-lived and already in the cache of the positive responses to stub resolver for good queries on TLDs, because
recursive resolver; thus, getting faster positive responses is a non- the data for those zones is usually long-lived and already in the
goal of this design. cache of the recursive resolver; thus, getting faster positive
responses is a non-goal of this design.
This design explicitly only allows the new root zone server to be run This design explicitly only allows the new root zone server to be run
on a loopback address. This prevents the server from serving on a loopback address, in order to prevent the server from serving
authoritative answers to any system other than the recursive authoritative answers to any system other than the recursive
resolver. resolver. [[ Other people have said that they might propose a
similar design that does not use the loopback, but instead uses a new
root zone server that only responds to queries from a very limited
number of addresses. ]]
It is important to note that this design is being described here is
not considered a "best practice". In fact, many people feel that it
is an excessively risky practice because it introduces a new
operational piece to local DNS operations where there was not one
before. The advantages listed above do not come free: if this new
system does not work correctly, users can get bad data, or the entire
recursive resolution system might fail in ways that are hard to
diagnose.
This design requires the addition of authoritative name server This design requires the addition of authoritative name server
software running on the same machine as the recursive resolver. software running on the same machine as the recursive resolver.
Thus, recursive resolver software such as BIND will not need to add Thus, recursive resolver software such as BIND will not need to add
much new functionality, but recursive resolver software such as much new functionality, but recursive resolver software such as
Unbound will need to be able to talk to an authoritative server (such Unbound will need to be able to talk to an authoritative server (such
as NSD) running on the same host. as NSD) running on the same host.
1.1. Requirements Notation 1.1. Requirements Notation
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(including all DNSSEC-related records). (including all DNSSEC-related records).
o The system MUST be able to run an authoritative server on one of o The system MUST be able to run an authoritative server on one of
the IPv4 loopback addresses (that is, an address in the range the IPv4 loopback addresses (that is, an address in the range
127/8). 127/8).
A corollary of the above list is that authoritative data in the root A corollary of the above list is that authoritative data in the root
zone used on the local authoritative server MUST be identical to the zone used on the local authoritative server MUST be identical to the
same data in the root zone for the DNS. It is possible to change the same data in the root zone for the DNS. It is possible to change the
unsigned data (the glue records) in the copy of the root zone, but unsigned data (the glue records) in the copy of the root zone, but
such changes are likely to cause problems for the recursive server such changes could cause problems for the recursive server that
that accesses the local root zone. accesses the local root zone, and therefore any changes to the glue
records SHOULD NOT be made.
3. Operation of the Root Zone on the Loopback Address 3. Operation of the Root Zone on the Loopback Address
The operation of an authoritative server for the root in the system The operation of an authoritative server for the root in the system
described here can be done separately from the operation of the described here can be done separately from the operation of the
recursive resolver. recursive resolver.
The steps to set up the root zone are: The steps to set up the root zone are:
1. Retrieve a copy of the root zone. (See Appendix A for some 1. Retrieve a copy of the root zone. (See Appendix A for some
current locations of sources.) current locations of sources.)
2. Start the authoritative server with the root zone on a loopback 2. Start the authoritative server with the root zone on a loopback
address that is not in use. This would typically be 127.0.0.1, address that is not in use. This would typically be 127.0.0.1,
but if that address is in use, any address in 127/8 is but if that address is in use, any address in 127/8 is
acceptable. acceptable.
The contents of the root zone must be refreshed using the timers from The contents of the root zone MUST be refreshed using the timers from
the SOA record in root zone, as described in [RFC1035]. If the the SOA record in root zone, as described in [RFC1035]. If the
contents of the zone cannot be refreshed before the expire time, the contents of the zone cannot be refreshed before the expire time, the
server MUST return a SERVFAIL error response for all queries until server MUST return a SERVFAIL error response for all queries until
the zone can be successfully be set up again. the zone can be successfully be set up again.
In the event that refreshing the contents of the root zone fails, the
results can be disastrous. For example, sometimes all the NS records
for a TLD are changed in a short period of time; if the local root
zone refreshing is broken during that time, the recursive resolver
will have bad data for the entire TLD zone.
An administrator using the procedure in this document SHOULD have an
automated method to check that the contents of the local root zone
are being refreshed. One way to do this is to have a separate
process that periodically checks the SOA of the root zone from the
local root zone and makes sure that they are changing. At the time
that this document is published, the SOA for the root zone is the
digital representation of the current date with a two-digit counter
appended, and the SOA is changed every day even if the contents of
the root zone are unchanged. For example, the SOA of the root zone
on January 2, 2015 was 2015010201. A process can use this fact to
create a check for the contents of the local root zone (using a
program not specified in this document).
4. Using the Root Zone Server on the Loopback Address 4. Using the Root Zone Server on the Loopback Address
A recursive resolver that wants to use a root zone server operating A recursive resolver that wants to use a root zone server operating
as described in Section 3 simply specifies the local address as the as described in Section 3 simply specifies the local address as the
place to look when it is looking for information from the root. All place to look when it is looking for information from the root. All
responses from the root server must be validated using DNSSEC. responses from the root server must be validated using DNSSEC.
Note that using this configuration will cause the recursive resolver Note that using this configuration will cause the recursive resolver
to fail if the local root zone server fails. See Appendix B for more to fail if the local root zone server fails. See Appendix B for more
discussion of this for specific software. discussion of this for specific software.
To test the proper operation of the recursive resolver with the local To test the proper operation of the recursive resolver with the local
root server, use a DNS client to send a query for the SOA of the root root server, use a DNS client to send a query for the SOA of the root
to the recursive server. Make sure the response that comes back does to the recursive server. Make sure the response that comes back has
not have the AD bit in the message header set. the AA bit in the message header set to 0.
5. IANA Considerations 5. IANA Considerations
This document requires no action from the IANA. This document requires no action from the IANA.
6. Security Considerations 6. Security Considerations
A system that does not follow the DNSSEC-related requirements given A system that does not follow the DNSSEC-related requirements given
in Section 2 can be fooled into giving bad responses in the same way in Section 2 can be fooled into giving bad responses in the same way
as any recursive resolver that does not do DNSSEC validation on as any recursive resolver that does not do DNSSEC validation on
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The editors fully acknowledge that this is not a new concept, and The editors fully acknowledge that this is not a new concept, and
that we have chatted with many people about this. In fact, this that we have chatted with many people about this. In fact, this
concept may already have been implemented without the knowledge of concept may already have been implemented without the knowledge of
the authors. For example, Bill Manning described a similar solution the authors. For example, Bill Manning described a similar solution
but to a very different problem (intermittent connectivity, instead but to a very different problem (intermittent connectivity, instead
of constant but slow connectivity) in his doctoral dissertation in of constant but slow connectivity) in his doctoral dissertation in
2013 [Manning2013]. 2013 [Manning2013].
Evan Hunt contributed greatly to the logic in the requirements. Evan Hunt contributed greatly to the logic in the requirements.
Other significant contributors include Wouter Wijngaards, Tony Hain, Other significant contributors include Wouter Wijngaards, Tony Hain,
Doug Barton, and Greg Lindsay. Doug Barton, and Greg Lindsay. The authors also received many off-
line comments about making the document clear that this was just a
description of a way to operate a root zone on localhost, and not a
recommendation to do so.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
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all the DNSSEC records needed for validation. Currently, there are all the DNSSEC records needed for validation. Currently, there are
three sources of the root zone supported by ICANN: three sources of the root zone supported by ICANN:
o From ICANN via FTP at ftp://rs.internic.net/domain/root.zone o From ICANN via FTP at ftp://rs.internic.net/domain/root.zone
o From ICANN via HTTP at http://www.internic.net/domain/root.zone o From ICANN via HTTP at http://www.internic.net/domain/root.zone
o From ICANN by AXFR from DNS servers at xfr.lax.dns.icann.org and o From ICANN by AXFR from DNS servers at xfr.lax.dns.icann.org and
xfr.cjr.dns.icann.org xfr.cjr.dns.icann.org
Currently, the root can be retrieved by zone transfer (AXFR) from the Currently, the root can also be retrieved by zone transfer (AXFR)
following root server operators: from the following root server operators:
o b.root-servers.net o b.root-servers.net
o c.root-servers.net
o c.root-servers.net
o f.root-servers.net o f.root-servers.net
o g.root-servers.net o g.root-servers.net
o k.root-servers.net o k.root-servers.net
Appendix B. Example Configurations of Common Implementations Appendix B. Example Configurations of Common Implementations
This section shows fragments of configurations for some popular This section shows fragments of configurations for some popular
recursive server software that is believed to correctly implement the recursive server software that is believed to correctly implement the
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The IPv4 and IPv6 addresses in this section were checked recently by The IPv4 and IPv6 addresses in this section were checked recently by
testing for AXFR over TCP from each address for the known single- testing for AXFR over TCP from each address for the known single-
letter names in the root-servers.net zone. letter names in the root-servers.net zone.
The examples here use a loopback address of 127.12.12.12, but typical The examples here use a loopback address of 127.12.12.12, but typical
installations will use 127.0.0.1. The different address is used in installations will use 127.0.0.1. The different address is used in
order to emphasize that the root server does not need to be on the order to emphasize that the root server does not need to be on the
device at "localhost". device at "localhost".
[[ We were told that PowerDNS will soon be able to be configured to
meet the requirements in this document. We'll add that configuration
when/if someone contributes it. ]]
B.1. Example Configuration: BIND 9.9 B.1. Example Configuration: BIND 9.9
BIND acts both as a recursive resolver and an authoritative server. BIND acts both as a recursive resolver and an authoritative server.
Because of this, there is "fate sharing" between the two servers in Because of this, there is "fate sharing" between the two servers in
the following configuration. That is, if the root server dies, it is the following configuration. That is, if the root server dies, it is
likely that all of BIND is dead. likely that all of BIND is dead.
Using this configuration, queries for information in the root zone Using this configuration, queries for information in the root zone
are returned with the AA bit not set. are returned with the AA bit not set.
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