Internet DRAFT - draft-jabley-as112-being-attacked-help-help
draft-jabley-as112-being-attacked-help-help
Network Working Group J. Abley
Internet-Draft Afilias
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I'm Being Attacked by PRISONER.IANA.ORG!
draft-jabley-as112-being-attacked-help-help-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
Many sites connected to the Internet make use of IPv4 addresses which
are not globally unique. Examples are the addresses designated in
RFC1918 for private use within individual sites.
Hosts should never normally send reverse DNS queries for those
addresses on the public Internet. However, such queries are
frequently observed. Authority servers are deployed to provide
authoritative answers to such queries as part of a loosely-
coordinated effort known as the AS112 project.
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Since queries sent to AS112 servers are usually not intentional, the
replies received back from those servers are typically unexpected.
Unexpected inbound traffic can trigger alarms on intrusion detection
systems and firewalls, and operators of such systems often mistakenly
believe that they are being attacked.
This document provides background information and technical advice to
those firewall operators.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Private-Use Addresses . . . . . . . . . . . . . . . . . . . . 4
3. Reverse DNS . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Reverse DNS for Private-Use Addresses . . . . . . . . . . . . 6
5. AS112 Nameservers . . . . . . . . . . . . . . . . . . . . . . 7
6. Inbound Traffic from AS112 Servers . . . . . . . . . . . . . . 8
7. Corrective Measures . . . . . . . . . . . . . . . . . . . . . 9
8. AS112 Contact Information . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Change History . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. Introduction
Readers of this document may well have experienced an alarm from a
firewall or an intrusion-detection system, triggered by unexpected
inbound traffic from the Internet. The traffic probably appeared to
originate from one of the following hosts:
o PRISONER.IANA.ORG (192.175.48.1)
o BLACKHOLE-1.IANA.ORG (192.175.48.6)
o BLACKHOLE-2.IANA.ORG (192.175.48.42)
The published contacts for those hosts may well have suggested that
you consult this document.
If you are following up on such an event, you are encouraged to
follow your normal security procedures and take whatever action you
consider to be be appropriate. This document contains information
which may assist you.
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2. Private-Use Addresses
Many sites connected to the Internet make use of address blocks
designated in [RFC1918] for private use. Examples of such addresses
are 10.1.30.20, 172.18.24.100 and 192.168.1.1.
Because these ranges of addresses are used by many sites all over the
world, each individual address can only ever have local significance.
For example, the host numbered 192.168.18.234 in one site almost
certainly has nothing to do with a host with the same address located
in a different site.
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3. Reverse DNS
The Domain Name System (DNS) [RFC1034] can be used to obtain a name
for a particular network address. The process by which this happens
is as follows:
1. The network address is rearranged in order to construct a name
which can be looked up in the DNS. For example, the IPv4 address
10.3.70.25 corresponds to the DNS name 25.70.3.10.IN-ADDR.ARPA.
2. A DNS query is constructed for that name, requesting a DNS record
of the type "PTR".
3. The DNS query is sent to a resolver.
4. If a response is received in response to the query, the answer
will typically indicate either the hostname corresponding to the
network address, or the fact that no hostname can be found.
This procedure is generally carried out automatically by software,
and is hence largely hidden from users and administrators.
Applications might have reason to look up an IP address in order to
gather extra information for a log file, for example.
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4. Reverse DNS for Private-Use Addresses
As noted in Section 2, private-use addresses have only local
significance. This means that sending queries out to the Internet is
not sensible: there is no way for the public DNS to provide a useful
answer to a question which has no global meaning.
Despite the fact that the public DNS cannot provide answers, many
sites have misconfigurations in the way they connect to the Internet
which results to such queries relating to internal infrastructure
being sent outside the site. From the perspective of the public DNS,
these queries are junk -- they cannot be answered usefully and result
in unnecessary traffic being received by the nameservers which
underpin the operation of the public DNS (the so-called root
servers).
To isolate this traffic, and reduce the load on the rest of the DNS
infrastructure, dedicated servers have been deployed in the Internet
to receive and reply to these junk queries. These servers are
deployed in many places in a loosely-coordinated effort known as the
"AS112 Project". More details about the AS112 Project can be found
at <http://www.as112.net/>.
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5. AS112 Nameservers
The nameservers responsible for answering queries relating to
private-use addresses are as follows:
o PRISONER.IANA.ORG (192.175.48.1)
o BLACKHOLE-1.IANA.ORG (192.175.48.6)
o BLACKHOLE-2.IANA.ORG (192.175.48.42)
A request sent to one of these servers will result in a response
being returned to the client. The response will typically be a UDP
datagram, although it's perfectly valid for requests to be made over
TCP. In both cases the source port of packets returning to the site
which originated the DNS request will be 53.
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6. Inbound Traffic from AS112 Servers
Where firewalls or intrusion detection systems (IDS) are configured
to block traffic received from AS112 servers, superficial review of
the traffic may seem alarming to site administrators.
o Since requests directed ultimately to AS112 servers are usually
triggered automatically by applications, review of firewall logs
may indicate a large number of policy violations occurring over an
extended period of time.
o Where responses from AS112 servers are blocked by firewalls, hosts
will often retry, often with a relatively high frequency. This
can cause inbound traffic to be misclassified as a denial-of-
service (DoS) attack. In some case the source ports used by
individual hosts for successive retries increases in a predictable
fashion (e.g. monotonically), which can cause the replies from the
AS112 server to resemble a port scan.
o A site administrator may attempt to perform active measurement of
the remote host in response to alarms raised by inbound traffic,
e.g. initiating a port scan in order to gather information about
the host which is apparently attacking the site. Such a scan will
usually result in additional inbound traffic to the site
performing the measurement, e.g. an apparent flood of ICMP
messages which may trigger additional firewall alarms and
obfuscate the process of identifying the original problem traffic.
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7. Corrective Measures
A site which receives responses from one of the nameservers listed in
Section 5 is probably under no immediate danger, and the traffic
associated with those responses probably requires no emergency action
by the site concerned. However, this document cannot aspire to
dictate the security policy of individual sites, and it is recognised
that many sites will have perfectly valid policies which dictate that
corrective measures should be taken to stop the responses from AS112
servers.
It should be noted, however, that the operators of AS112 nameservers
which are generating the responses described in this document are not
ultimately responsible for the inbound traffic received by the site:
that traffic is generated in response to queries which are sent out
from the site, and so the only effective measures to stop the inbound
traffic is to prevent the original queries from being made.
Possible measures which might be taken to prevent these queries
include:
1. Stop hosts from making these reverse DNS queries in the first
place. In some cases servers can be configured not to perform
reverse DNS lookups, for example. As a general site-wide
approach, however, this measure is frequently difficult to
implement due to the large number of hosts and applications
involved.
2. Block reverse DNS queries to the AS112 servers from leaving the
site using firewalls between the site and the Internet. Although
this might appear to be sensible, such a measure might have
unintended consequences: the inability to receive an answer to
reverse DNS queries might lead to long DNS lookup timeouts, for
example, which could cause applications to malfunction.
3. Configure all DNS resolvers in the site to answer authoritatively
for the zones corresponding to the private-use address blocks in
use. This should prevent resolvers from ever needing to send
these queries to the public DNS. Guidance and recommendations
for this aspect of resolver configuration can be found in
[I-D.andrews-full-service-resolvers].
4. Implement a private AS112 node within the site. Guidance for
constructing an AS112 node may be found in [I-D.jabley-as112-
ops].
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8. AS112 Contact Information
Operational contact information for the network addresses of AS112
servers is registered with Regional Internet Registries (RIRs).
Readers who continue to have concerns about traffic received from
AS112 servers after reading this document are encouraged to contact
the AS112 Network Operations Centre.
More information about the AS112 project can be found at
<http://www.as112.net/>.
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9. IANA Considerations
The AS112 nameservers are all named under the domain IANA.ORG (see
Section 5). The IANA is the organisation responsible for the
coordination of many technical aspects of the Internet's basic
infrastructure. The AS112 project nameservers provide a public
service to the Internet which is sanctioned by and operated in
coordination with the IANA.
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10. Security Considerations
The purpose of this document is to help site administrators properly
identify traffic received from AS112 nodes, and to provide background
information to allow appropriate measures to be taken in response to
it.
Hosts should never normally send queries to AS112 servers: queries
relating to private-use addresses should be answered locally within a
site. Hosts which send queries to AS112 servers may well leak
information relating to private infrastructure to the public network,
which could represent a security risk.
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11. References
11.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
11.2. Informative References
[I-D.andrews-full-service-resolvers]
Andrews, M., "Configuration Issues Facing Full Service DNS
Resolvers In The Presence of Private Network Addressing",
draft-andrews-full-service-resolvers-02 (work in
progress), February 2006.
[I-D.jabley-as112-ops]
Abley, J. and W. Maton, "AS112 Nameserver Operations",
June 2006.
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Appendix A. Change History
This section to be removed prior to publication.
It is proposed that this document be published as an informational
RFC.
00 Initial draft.
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Author's Address
Joe Abley
Afilias Canada Corp.
Suite 204, 4141 Yonge Street
Toronto, ON M2P 2A8
Canada
Phone: +1 416 673 4176
Email: jabley@ca.afilias.info
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