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I'm Being Attacked by PRISONER.IANA.ORG!
RFC 6305

Document Type RFC - Informational (July 2011)
Authors William F. Maton , Joe Abley
Last updated 2018-12-20
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
IESG Responsible AD Ron Bonica
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RFC 6305
Internet Engineering Task Force (IETF)                          J. Abley
Request for Comments: 6305                                         ICANN
Category: Informational                                         W. Maton
ISSN: 2070-1721                                                 NRC-CNRC
                                                               July 2011

                I'm Being Attacked by PRISONER.IANA.ORG!


   Many sites connected to the Internet make use of IPv4 addresses that
   are not globally unique.  Examples are the addresses designated in
   RFC 1918 for private use within individual sites.

   Hosts should never normally send DNS reverse-mapping queries for
   those addresses on the public Internet.  However, such queries are
   frequently observed.  Authoritative servers are deployed to provide
   authoritative answers to such queries as part of a loosely
   coordinated effort known as the AS112 project.

   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.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and Target Audience  . . . . . . . . . . . . . . . 3
   2.  Private-Use Addresses . . . . . . . . . . . . . . . . . . . . . 3
   3.  DNS Reverse Mapping . . . . . . . . . . . . . . . . . . . . . . 3
   4.  DNS Reverse Mapping for Private-Use Addresses . . . . . . . . . 4
   5.  AS112 Nameservers . . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Inbound Traffic from AS112 Servers  . . . . . . . . . . . . . . 5
   7.  Corrective Measures . . . . . . . . . . . . . . . . . . . . . . 5
   8.  AS112 Contact Information . . . . . . . . . . . . . . . . . . . 6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   10. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     12.1.  Normative References . . . . . . . . . . . . . . . . . . . 7
     12.2.  Informative References . . . . . . . . . . . . . . . . . . 7

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1.  Introduction and Target Audience

   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 several hosts discussed further below.

   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 appropriate.  This document contains information that
   may assist you.

2.  Private-Use Addresses

   Many sites connected to the Internet make use of address blocks
   designated in [RFC1918] for private use.  One example of such
   addresses is

   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 in one site almost
   certainly has nothing to do with a host with the same address located
   in a different site.

3.  DNS Reverse Mapping

   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
       that can be looked up in the DNS.  For example, the IPv4 address corresponds to the DNS name

   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 hence is largely hidden from users and administrators.

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   Applications might have reason to look up an IP address in order to
   gather extra information for a log file, for example.

4.  DNS Reverse Mapping 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 that 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;
   this results in 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 reverse DNS (the so-called reverse
   servers [RFC5855], which serve "IN-ADDR.ARPA").

   To isolate this traffic and reduce the load on the rest of the
   reverse 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 <>.

5.  AS112 Nameservers

   The nameservers responsible for answering queries relating to
   private-use addresses are as follows:




   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
   that originated the DNS request will be 53.

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6.  Inbound Traffic from AS112 Servers

   Where firewalls or intrusion detection systems (IDSs) 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 cases, the source ports used by
      individual hosts for successive retries increase 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 that may trigger additional firewall alarms and obfuscate
      the process of identifying the originally problematic traffic.

7.  Corrective Measures

   A site that 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 that dictate that
   corrective measures should be taken to stop the responses from AS112

   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 that 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.

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   Possible measures that might be taken to prevent these queries

   1.  Stop hosts from making these DNS reverse-mapping queries in the
       first place.  In some cases, servers can be configured not to
       perform DNS reverse-mapping 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

   2.  Block DNS reverse-mapping 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 DNS reverse-mapping queries might lead to
       long DNS lookup timeouts, for example, which could cause
       applications to malfunction.  (It may also lead to the belief
       that the Internet or the local network is down.)

   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

   4.  Implement a private AS112 node within the site.  Guidance for
       constructing an AS112 node may be found in [RFC6304].

8.  AS112 Contact Information

   More information about the AS112 project can be found at

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 that is sanctioned by and operated in loose
   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

   Hosts should never normally send queries to AS112 servers: queries
   relating to private-use addresses should be answered locally within a
   site.  Hosts that send queries to AS112 servers may well leak
   information relating to private infrastructure to the public network;
   this could represent a security risk.

11.  Acknowledgements

   The authors wish to acknowledge the assistance of S. Moonesamy in the
   preparation of this document.

12.  References

12.1.  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.

12.2.  Informative References

   [RFC5855]  Abley, J. and T. Manderson, "Nameservers for IPv4 and IPv6
              Reverse Zones", BCP 155, RFC 5855, May 2010.

   [RFC6303]  Andrews, M., "Locally Served DNS Zones", BCP 163,
              RFC 6303, July 2011.

   [RFC6304]  Abley, J. and W. Maton, "AS112 Nameserver Operations",
              RFC 6304, July 2011.

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Authors' Addresses

   Joe Abley
   4676 Admiralty Way, Suite 330
   Marina del Rey, CA  90292

   Phone: +1 519 670 9327

   William F. Maton Sotomayor
   National Research Council of Canada
   1200 Montreal Road
   Ottawa, ON  K1A 0R6

   Phone: +1 613 993 0880

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