draft-ietf-dnsop-reflectors-are-evil-05.txt   draft-ietf-dnsop-reflectors-are-evil-06.txt 
Network Working Group J. Damas Network Working Group J. Damas
Internet-Draft ISC Internet-Draft ISC
Intended status: Best Current F. Neves Intended status: BCP F. Neves
Practice Registro.br Expires: March 5, 2009 Registro.br
Expires: June 5, 2008 December 3, 2007 September 1, 2008
Preventing Use of Recursive Nameservers in Reflector Attacks Preventing Use of Recursive Nameservers in Reflector Attacks
draft-ietf-dnsop-reflectors-are-evil-05.txt draft-ietf-dnsop-reflectors-are-evil-06.txt
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This Internet-Draft will expire on June 5, 2008. This Internet-Draft will expire on March 5, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract Abstract
This document describes ways to prevent the use of default configured This document describes ways to prevent the use of default configured
recursive nameservers as reflectors in Denial of Service (DoS) recursive nameservers as reflectors in Denial of Service (DoS)
attacks. Recommended configuration as measures to mitigate the attacks. Recommended configuration as measures to mitigate the
attack are given. attack are given.
Table of Contents Table of Contents
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3. Problem Description 3. Problem Description
Because most DNS traffic is stateless by design, an attacker could Because most DNS traffic is stateless by design, an attacker could
start a DoS attack in the following way: start a DoS attack in the following way:
1. The attacker starts by configuring a record on any zone he has 1. The attacker starts by configuring a record on any zone he has
access to, normally with large RDATA and TTL. access to, normally with large RDATA and TTL.
2. Taking advantage of clients on non-BCP38 networks, the attacker 2. Taking advantage of clients on non-BCP38 networks, the attacker
then crafts a query using the source address of their target then crafts a query using the source address of their target
victim and sends it to an open recursive nameserver (ORNS). victim and sends it to an open recursive nameserver.
3. Each open recursive nameserver proceeds with the resolution, 3. Each open recursive nameserver proceeds with the resolution,
caches the record and finally sends it to the target. After this caches the record and finally sends it to the target. After this
first lookup, access to the authoritative nameservers is normally first lookup, access to the authoritative nameservers is normally
no longer necessary. The record will remain cached for the no longer necessary. The record will remain cached for the
duration of the TTL at the open recursive nameserver even if it's duration of the TTL at the open recursive nameserver even if it's
deleted from the zone. deleted from the zone.
4. Cleanup of the zone might, depending on the implementation used 4. Cleanup of the zone might, depending on the implementation used
in the open recursive nameserver, afford a way to clean the in the open recursive nameserver, afford a way to clean the
cached record from the open recursive nameserver. This would cached record from the open recursive nameserver. This would
possibly involve queries luring the open recursive nameserver to possibly involve queries luring the open recursive nameserver to
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knit community, some nameserver implementations have been made knit community, some nameserver implementations have been made
available with default configurations that when used for recursive available with default configurations that when used for recursive
nameservers made the server accessible to all hosts on the Internet. nameservers made the server accessible to all hosts on the Internet.
For years this was a convenient and helpful configuration, enabling For years this was a convenient and helpful configuration, enabling
wider availability of services. As this document aims to make wider availability of services. As this document aims to make
apparent, it is now much better to be conscious of ones own apparent, it is now much better to be conscious of ones own
nameserver services and focus the delivery of services on the nameserver services and focus the delivery of services on the
intended audience of those services, be they a university campus, an intended audience of those services, be they a university campus, an
enterprise or an ISP's customers. The target audience also includes enterprise or an ISP's customers. The target audience also includes
operators of small network operators and private server managers who operators of small networks and private server managers who decide to
decide to operate nameservers with the aim of optimising their DNS operate nameservers with the aim of optimising their DNS service, as
service, as these are more likely to use default configurations as these are more likely to use default configurations as shipped by
shipped by implementors. implementors.
4. Recommended Configuration 4. Recommended Configuration
In this section we describe the Best Current Practice for operating In this section we describe the Best Current Practice for operating
recursive nameservers. Following these recommendations would reduce recursive nameservers. Following these recommendations would reduce
the chances of having a given recursive nameserver be used for the the chances of having a given recursive nameserver be used for the
generation of an amplification attack. generation of an amplification attack.
The generic recommendation to nameserver operators is to use the The generic recommendation to nameserver operators is to use the
means provided by the implementation of choice to provide recursive means provided by the implementation of choice to provide recursive
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Multihomed Network" [BCP84] maybe a useful additional reference. Multihomed Network" [BCP84] maybe a useful additional reference.
By default, nameservers SHOULD NOT offer recursive service to By default, nameservers SHOULD NOT offer recursive service to
external networks. external networks.
5. Security Considerations 5. Security Considerations
This document does not create any new security issues for the DNS This document does not create any new security issues for the DNS
protocol, it deals with a weakness in implementations. protocol, it deals with a weakness in implementations.
Deployment of SIG(0) transaction security should consider the caveats
with SIG(0) computational expense as it uses public key cryptography
rather than the symmetric keys used by TSIG. In addition, the
identification of the appropriate keys needs similar mechanisms to
those for deploying TSIG, or alternatively, the use of DNSSEC
signatures (RRSIGs) over the KEY RRs if published in DNS. This will
in turn require the appropriate management of DNSSEC trust anchors.
6. Acknowledgments 6. Acknowledgments
The authors would like to acknowledge the helpful input and comments The authors would like to acknowledge the helpful input and comments
of Joe Abley, Olafur Gudmundsson, Pekka Savola, Andrew Sullivan and of Joe Abley, Olafur Gudmundsson, Pekka Savola, Andrew Sullivan and
Tim Polk. Tim Polk.
7. IANA Considerations 7. IANA Considerations
This document does not define a registry and does not require any This document does not define a registry and does not require any
IANA action. IANA action.
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