Domain Name System Operations                                   P. Vixie
Internet-Draft                                   Farsight Security, Inc.
Intended status: Informational                               V. Schryver
Expires: April 14, 2017                                Rhyolite Software
                                                        October 11, 2016

                         Response Policy Zones


   This document describes a method for expressing DNS response policy
   inside a specially constructed DNS zone, and for processing the
   contents of such response policy zones (RPZ) inside recursive name
   servers.  These "DNS Firewalls" are widely used in fighting Internet
   crime and abuse.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 14, 2017.

Copyright Notice

   Copyright (c) 2016 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

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may not be modified, and derivative works of it may not
   be created, except to format it for publication as an RFC or to
   translate it into languages other than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Zone Format . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Policy Actions  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Policy Triggers . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Subscriber Behavior . . . . . . . . . . . . . . . . . . . . .   9
   6.  Producer Behavior . . . . . . . . . . . . . . . . . . . . . .  11
   7.  History and Evolution . . . . . . . . . . . . . . . . . . . .  12
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     10.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   This document describes DNS Firewalls or a method of expressing DNS
   [RFC1034] policy information inside specially constructed DNS zones,
   allowing DNS reputation data producers and subscribers to cooperate
   in the application of policies to real time DNS responses.  Using
   this policy information, DNS resolution for low-reputation DNS data
   can be made to deliberately fail or to return local data such as an
   alias to a "walled garden".  A full description of the expressible
   policies is given in Section 2.

   Configuration examples using ISC BIND Version 9 (BIND9) [ISC-ARM] are
   given, because work to add RPZ to that platform was started in 2009.
   The RPZ specification itself is free to implement and free to use in
   operation, and so we expect other recursive DNS implementations to
   also implement DNS Firewalls as described by the RPZ specification.

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2.  Zone Format

   A DNS Response Policy Zone (RPZ) is a DNS zone.  As such its contents
   can be transferred between servers DNS in whole (AXFR) [RFC5936] or
   incrementally as changes occur (IXFR) [RFC1995], authenticated and
   protected by TSIG transaction signatures [RFC2845], and expedited by
   real time change notifications (NOTIFY) [RFC1996], all subject to
   familiar DNS access controls.  An RPZ need not support query access
   since query access is never required.  It is the zone transfer of RPZ
   content from producers to subscribers which effectively publishes the
   policy data, and it is the subscriber's server configuration which
   promotes RPZ payload data into DNS control plane data.

   To be a valid DNS zone, an RPZ is required to have an SOA record and
   at least one NS record at its apex.  The SOA record is real, with a
   serial number used for NOTIFY and IXFR and timers used for AXFR and
   IXFR.  The MNAME field or domain name of the primary source of the
   zone and the RNAME field or mailbox of the person responsible for the
   zone are often used by RPZ providers to label their policy zones.

   Because query access is never required, an RPZ's apex NS record will
   never be used and no parent delegation is required.  The zone name of
   the NS record need not be a unique fully qualified domain name.  By
   convention, a single NS record having the deliberately bogus value
   "LOCALHOST" is used as a placeholder.  The zone's name can be fully
   qualified to show the identity of its producer or maintainer.

   Like any DNS zone, an RPZ consists of RRsets or sets of resource
   records (RRs) with a common owner name and type.  The owner names or
   left hand sides of RRsets other than the SOA and NS express policy
   triggers or characteristics of DNS response that require action.  The
   action enjoined by a policy trigger is encoded in the rdata or right
   hand sides of the records.

   All POLICY described here are from RPZ Format 1 unless otherwise
   noted.  Policy triggers from a higher format number than a recursive
   name server's implementation level are expected to be invisible to
   that implementation.  Policy actions from a higher format number are
   likely to be misinterpreted as CNAME local data by older

3.  Policy Actions

   An RPZ resource record can specify any of five different results or

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      A single resource record (RR) consisting of a CNAME whose target
      is the root domain (.) will cause a response of NXDOMAIN to be
      returned.  This is the most commonly used RPZ action.

      A single RR consisting of a CNAME whose target is the wildcard
      top-level domain (*.) will cause a response of NODATA (ANCOUNT=0)
      to be returned regardless of query type.

      [Format 3] It is sometimes necessary to exempt some DNS responses
      from the response policy rule that covers an entire domain or a
      large IP address block.  Exempting some clients of a DNS resolver
      from all RPZ rewriting can also be useful for research into
      attackers and debugging.  The PASSTHRU action encoded as a CNAME
      with a target or right hand side of "rpz-passthru." overrides
      lower precedence policies.

      This policy zone record

      CNAME   rpz-passthru.

      would exempt requests for from NXDOMAIN policy or
      action of the following record:

           CNAME   .
           *        CNAME   .

      The deprecated [Format 1] encoding of the PASSTHRU action was a
      CNAME with a target equal to the QNAME field of the DNS request.
      That encoding could not be used with some desirable triggers.

      The "DROP" policy that consists of discarding the request and
      response is specified by a CNAME whose target is "rpz-drop".  For
      example, with

          CNAME   rpz-drop.

      nothing is sent to a DNS client trying to resolve, not
      even a DNS error response.

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      The "TCP-Only" policy is specified by a CNAME whose target is
      "rpz-tcp-only".  It changes UDP responses to short, truncated DNS
      responses that require the DNS client to try again with TCP.  It
      is used to mitigate distributed DNS reflection attacks and is
      similar to the "slip" parameter of DNS Response Rate Limiting
      (RRL) [ISC-RRL].

   Local Data
      Any other RRset that is not the RPZ encoding of NXDOMAIN (.) or
      NODATA (*.) and not a CNAME with a target domain name starting
      with "rpz-", specifies local data used to generate synthetic DNS
      responses.  If any local data policy actions are present, then any
      questions for RR types that are not present in the local data will
      be answered as NODATA (ANCOUNT=0) as if this DNS server were
      authoritative for the query name.  The most common local data is a
      CNAME RR pointing to a local walled garden.  Such CNAME RRs are
      distinguishable from other rpz actions because the CNAME target
      name will not be the root (.), root wildcard (*.), or be a
      subdomain of a top level domain that starts with "rpz-".

      [Format 3] A special form of local data involves a CNAME RR with a
      wildcarded target name.  Wildcards are not valid as CNAME targets
      in ordinary DNS zones.  This special form causes the QNAME to be
      prepended to the wildcarded target to communicate the triggering
      QNAME value to the the walled garden DNS server.  For example a
      policy action of "CNAME *.EXAMPLE.COM" and a query name of
      "EVIL.ORG." will result in a synthetic response of
      "EVIL.ORG CNAME EVIL.ORG.EXAMPLE.COM."  The purpose for this
      special form is query logging in the walled garden's DNS server.

4.  Policy Triggers

   All five types of RPZ triggers are encoded by RRset owner names in an

   Three of the types of triggers are based on target data (RDATA).
   Those policies are conceptually applied after recursion, so that the
   recursive DNS resolver's cache contains either nothing or "truth"
   even if this truth is hidden by current policy.  If the policy
   changes, the original data is available for processing under the
   changed policy.  The other types of policy trigger are independent of
   cache contents or recursion results.

      The QNAME policy trigger applies to requested domain names
      (QNAME).  The owner name of an RPZ QNAME policy RRset is the
      relativized name of the domain name about which policy is being

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      expressed.  For example, if the RPZ apex name is RPZ.EXAMPLE.ORG,
      an RRset at DOMAIN.COM.RPZ.EXAMPLE.ORG would affect responses to
      requests about DOMAIN.COM.  Wildcards also work, and so the owner
      name "*.DOMAIN.COM.RPZ.EXAMPLE.ORG" would trigger on queries to
      any subdomain of DOMAIN.COM.  To control the policy for both a
      name and its subdomains, two policy RRsets must be used, one for
      the domain itself and another for a wildcard sub-domain.  In the
      following example, queries for both DOMAIN.COM and all subdomains
      of DOMAIN.COM will result in synthetic NXDOMAIN responses.

           DOMAIN.COM          CNAME   .
           *.DOMAIN.COM        CNAME   .

   Response IP address [Format 2]
      The response IP policy trigger is based on target data (RDATA).
      It matches IP addresses that would otherwise appear in A and AAAA
      records in the "answer" section of a DNS response.  IP addresses
      the in "authority" and "additional" sections are not considered.
      Response IP policy RRsets have owner names that are sub-domains of
      "rpz-ip" relativized to the RPZ apex name, and an encoded IP
      address or block of addresses.

      IPv4 addresses are encoded as "prefix.B4.B3.B2.B1.rpz-ip".  The
      prefix length, "prefix", must be between 1 and 32.  All four
      bytes, B4, B3, B2, and B1, must be present and written in decimal
      ASCII.  B4 is the least significant octet of the IP address and B1
      is the most significant octet, just as in the IN-ADDR.ARPA naming

      IPv6 addresses are encoded in a format similar to the standard
      IPv6 text representation, "prefix.W8.W7.W6.W5.W4.W3.W2.W1.rpz-ip".
      Each of W8,...,W1 is a one to four digit hexadecimal ASCII number
      representing 16 bits of the IPv6 address with no leading zeroes
      and reversed as in IP6.ARPA.  All 8 words must be present unless a
      "zz" label is present.  "Zz" is analagous to the double-colon (::)
      in the standard IPv6 address representation.  The "zz" label is
      expanded to zero-fill the middle portion of the IPv6 address.  The
      prefix length must be between 1 and 128.  For example, to force an
      NXDOMAIN response whenever a truthful response would contain an
      "answer" section A RRset having an address in
      unless address is present, the RPZ would contain the

    CNAME   .
    CNAME   rpz-passthru.

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      In another example, to answer NODATA (ANCOUNT=0) whenever a
      truthful response would contain an answer AAAA RRset having an
      address 2001:0002::/48 unless address 2001:0002::3 was present,
      the RPZ would contain these records:

           48.zz.2.2001.rpz-ip     CNAME   *.
           128.3.zz.2.2001.rpz-ip  CNAME   rpz-passthru.

   Client IP address
      The IP addresses of DNS clients sending requests can also be
      triggers.  This can be useful for disabling RPZ rewriting for DNS
      clients used to test or investigate.  Client IP address triggers
      are encoded like response IP address triggers except that they are
      subdomains of rpz-client-ip instead of rpz-ip.  For example, the
      following would drop all requests from clients in
      and answer truthfull requests from a client at 2001:2::3.

           48.zz.2.2001.rpz-client-ip          CNAME *.
           128.3.zz.2.2001.rpz-client-ip   CNAME rpz-passthru.

   NSDNAME [Format 2]
      The NSDNAME policy trigger matches name server names (NS RR) of
      any name server which is in the data path for an RRset present in
      the answer section of a DNS response.  The data path is all
      delegation points from (and including) the root zone to the
      closest enclosing NS RRset for the owner name of the answering

      In other words, an NSDNAME trigger is checked by first considering
      the named servers (domain names in the NS records) for the query
      domain (QNAME), then the name servers for the parent of the query
      domain, and so on until the name servers for the root (.) have
      been checked.  This process stops immediately for a given trigger
      when the trigger is hit.

      This process can be expensive, especially when it comes to
      checking the many NS records for the top level domains and the
      root.  Because the name servers for the root and the TLDs are
      rarely used as RPZ triggers, common RPZ implementations have a
      "min-ns-dots" parameter that stops NSDNAME and NSIP checking

      Despite their costs, NSDNAME triggers can be more effective than
      QNAME and IP triggers.  Malefactors can more easily change their
      direct domain names and IP addresses detected by QNAME and IP

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      triggers than they can their change NS names and addresses in
      parent domains such as TLDs.

      NSDNAME policies are encoded as RRsets in sub-domains of
      "rpz-nsdname" but otherwise much like QNAME policies.  For
      example, to force an NXDOMAIN answer whenever a name server for
      the requested domain or one of its parents is NS.DOMAIN.COM, the
      RPZ would contain the following:

           NS.DOMAIN.COM.rpz-nsdname   CNAME .

      Some implementations of DNS RPZ will exhaustively discover all
      ancestral zone cuts above the query name and will learn the NS
      RRset at the apex of each delegated zone.  Other implementations
      will know only the zone cut information which has naturally come
      into the cache, which will often include only parent delegation
      name server names or "glue."  Since apex ("below the cut") NS
      RRsets and delegation NS RRsets need not exactly match, this can
      lead to instability in DNS RPZ behavior in the presence of zone
      cuts having differences between the NS RRsets above and below a
      zone cut.  This potential inconsistency must be taken into account
      when designing a security policy or testing DNS RPZ.

      The BIND9 and Unbound RPZ implementations use whatever NS RRsets
      that are in their caches unless there are none, in which case they
      recurse.  In practice this is best, because the authoritative apex
      NS RRsets of domains operated by malefactors is often peculiar.
      For example, RRs like " NS ." claiming that the root is
      authoritative are popular choices in malefactor apex NS RRsets.

   NSIP [Format 2]
      The NSIP policy trigger matches name server addresses (an A or
      AAAA RR that's been referenced by an NS RRset).  NSIP is much like
      NSDNAME (described above) except that the matching is by name
      server address rather than name server name.  NSIP policies are
      expressed as sub-domains of "rpz-nsip" and have the same sub-
      domain naming convention as described for response IP policy
      triggers above.

      In other words, an NSIP trigger is checked by first considering
      all of the IP address for all the named servers (or domain names
      in the NS records) for the query domain (QNAME), then the IP
      addresses for name servers for the parent of the qname, and so on
      until the name servers for the root (.) have been checked.  This
      process stops immediately when the trigger is hit.

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      This process can be very expensive, especially when it comes to
      checking the many NS and IP RRs for the TLDs and the root.
      Because the IP addresses of name servers for the root and the TLDs
      are rarely used as RPZ triggers, common RPZ implementations have a
      "min-ns-dots" parameter that stops NSIP and NSDNAME checking

      Nevertheless, NSIP triggers can be more effective than QNAME and
      IP triggers.  Malefactors can more easily change their direct
      domain names and IP addresses that QNAME and IP triggers detect
      than they can their change NS names and addresses that are in
      parent domains such as TLDs.

      As with NS Domain Name or NSDNAME triggers, some implementations
      of DNS RPZ will exhaustively discover all IP addresses (V4 and V6)
      associated with each name server name.  Other DNS RPZ
      implementations will only know the subset of IP addresses which
      have entered the cache naturally.  This can lead to instabilities
      in the DNS RPZ behavior since the natural entry of IP addresses
      into the cache is itself unstable.  This instability must be taken
      into account when designing a security policy or testing DNS RPZ.

      Also like NSDNAME triggers, the BIND9 and Unbound RPZ
      implementations use whatever A or AAAA RRsets that are in their
      caches for NS domains unless there are none, in which case they
      recurse.  In practice this is best, not only because the
      authoritative A and AAAA RRsets of name servers for the domains of
      malefactors are often imaginitive, but because even when they are
      reasonable, the authoritative DNS servers for their NS domains are
      often extremely slow or broken.

5.  Subscriber Behavior

   RPZs must be primary or secondary zones at subscriber recursive
   resolvers.  They can only be searched in a recursive server's own
   storage, because additional network transactions for DNS resolvers
   are extremely undesirable.

   By default, policies are applied only on DNS requests that ask for
   recursion (RD=1) and which either do not request DNSSEC metadata
   (DO=0) or for which no DNSSEC metadata exists.

   Policies are checked at each stage of resolving a domain name defined
   by a CNAME or DNAME record, stopping at the first CNAME in the chain
   with an applicable policy.  CNAME targets in a CNAME chain are
   checked as if they were query names.

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   If a policy trigger results in a modified answer, then that modified
   answer will include in its "authority" section the SOA RR of the DNS
   RPZ whose policy was used to generate the modified answer.  This SOA
   RR will tell both the fully qualified name of the DNS RPZ and the
   serial number of the policy data which was connected to the DNS
   control plane at the time the answer was modified.

   Response policy zones are loaded in the usual way.  For primary zones
   this may mean loading the contents of a local file into memory, or
   connecting to a database.  For secondary zones this means
   transferring the zone from the primary server using zone transfer
   such as IXFR [RFC1995] or AXFR [RFC5936].  It is strongly recommended
   that all secondary zone transfer relationships be protected with
   transaction signatures (DNS TSIG) and that real time change
   notification be enabled using the DNS NOTIFY protocol [RFC1996].

   DNS resolvers often have limited or no notion of a DNS zone.  They
   sometimes have special local zones, but generally have no
   implementations of IXFR, AXFR, or NOTIFY.  Therefore, an external
   module or daemon that maintains local copies of policy zones can be

   To connect the name server's control plane to the DNS RPZ data plane,
   an ordered list of RPZs should be supplied.  For each DNS RPZ in this
   list, it should be possible to specify an overriding policy action to
   be used for any policy triggers found in that RPZ.  These override
   policies should include NXDOMAIN, NODATA, PASSTHRU, GIVEN, and CNAME.
   GIVEN just explicitly reaffirms the default which is to respect all
   policy actions found in this DNS RPZ.  CNAME is an instance of "local
   data" which probably points to a walled garden service.

   It is possible for more than one policy trigger among the various DNS
   RPZs connected to the name server's control plane to match a given
   DNS query or DNS response.  The precedence rules for multiple matches
   are as follows:

   RPZ Ordering
      Policies from RPZs defined earlier ordered set of DNS RPZs are
      applied instead of those defined later.

   Within An RPZ
      Among policies from a single RPZ, QNAME policies are preferred
      over IP, IP policies are preferred over NSDNAME, and NSDNAME
      policies are preferred over NSIP.

   Name Length
      Among applicable QNAME or NSDNAME policies within a DNS RPZ,
      choose the policy that matches the smallest name.

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   Prefix Length
      Among applicable IP or NSIP policies, use the policy with the
      longest prefix length.

   Tie Breaker
      Given equal prefix lengths, use the policy that matches the
      smallest IP address.

   By default, when a QNAME or client IP address policy is triggered and
   the trigger is of such high precedence that it dominates all other
   possible triggers (e.g. it is in the first configured policy zone),
   the resolver continues to check and fill its cache by recursion as if
   it did not already know the answer.  This denies operators of
   authority servers for listed domains data about whether they are

6.  Producer Behavior

   A DNS RPZ producer should make every effort to ensure that
   incremental zone transfer (IXFR [RFC1995]) rather than full zone
   transfer (AXFR [RFC5936]) is used to move new policy data toward
   subscribers.  Also, real time zone change notifications (DNS NOTIFY
   [RFC1996] should be enabled and tested.  DNS RPZ subscribers are
   "stealth slaves" as described in RFC 1996, and each such server must
   be explicitly denoted in the master server's configuration.  Because
   DNS NOTIFY is a lazy protocol, it may be necessary to explicitly
   trigger the master server's "notify" logic after each update to the
   DNS RPZ.  These operational guidelines are to limit policy data
   latency, since minimal latency is critical to both prevention of
   crime and abuse, and to withdrawal of erroneous or outdated policy.

   In the data feed for disreputable domains, each addition or deletion
   or expiration can be handled using DNS UPDATE [RFC2136] to trigger
   normal DNS NOTIFY and subsequent DNS IXFR activity which can keep the
   subscribing servers well synchronized to the master RPZ.
   Alternatively, on some primary name servers (such as ISC BIND) it is
   possible to generate an entirely new primary RPZ file and have the
   server compute the differences between each new version and its
   predecessor.  In ISC BIND this option is called "ixfr-from-
   differences" and is known to be performant even for million-rule DNS
   RPZ's with significant churn on a minute by minute basis.

   It is good operational practice to include test records in each DNS
   RPZ to help that DNS RPZ's subscribers verify that response policy
   rewriting is working.  For example, a DNS RPZ might include a QNAME
   policy record for BAD.EXAMPLE.COM and an IP policy record for

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   installation by querying for BAD.EXAMPLE.COM which does not exist in
   real DNS.  If an answer is received it will be from the DNS RPZ.
   That answer will contain an SOA RR denoting the fully qualified name
   of the DNS RPZ itself.

7.  History and Evolution

   RPZ was previously described in a technical note from Internet
   Systems Consortium [ISC-RPZ].  A more up to date description was in
   chapter 6 of the "BIND 9 Administrator Reference Manual" [ISC-ARM].

   RPZ was designed by Paul Vixie and Vernon Schryver in 2009.  The
   initial implementation and first patch adding it to BIND was written
   by Vernon Schryver in late 2009.  Patches for various versions of
   BIND9 including 9.4, 9.6, and 9.7 were distributed from FTP servers
   at and 2010.

   If all RPZ triggers and actions had been foreseen at the start in
   2009, they would probably have been encoded differently.  Instead RPZ
   grew incrementally, and upward compatibility required continuing
   support of the original encodings.

   Today, with a number of commercial RPZ providers with many users and
   no functional problems with the encodings, any lack of aesthetic
   appeal is balanced by the ever increasing weight of the installed
   base.  For example, it is impossible to replace the original QNAME
   trigger encoding NXDOMAIN and NODATA policy action encodings with
   encodings that involve rpz-* psuedo-TLDs at RPZ providers without
   breaking the many existing RPZ subscriber installations.  The
   original, deprecated [Format 1] PASSTHRU encoding of a CNAME pointing
   to the trigger qname might still be in use in local, private policy
   zones, and so it is still recognized by RPZ subscriber

   The initial RPZ idea was only to deny the existence of objectionable
   domain names, and so there were only QNAME triggers and NXDOMAIN
   actions.  Given that single kind of trigger, encoding it as the owner
   name of a policy record was clearly best.  A CNAME pointing to the
   root domain (.) is a legal and valid but not generally useful record,
   and so that was the encoding for the NXDOMAIN action.  The encoding
   of the NODATA action as "CNAME *." followed similar reasoning.
   Requests for more kinds of triggers and actions required a more
   general scheme, and so they are encoded as CNAMES with targets in
   bogus TLDs owner names with DNS labels that start with "rpz_".

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8.  IANA Considerations

   No actions are required from IANA as result of the publication of
   this document.

9.  Security Considerations

   RPZ is a mechanism for providing "untruthful" DNS results from
   recursive servers.  However, RPZ does not increase the intrinsic DNS
   vulnerabilites at recursive servers to falsifying DNS data.  RPZ
   merely formalizes and facilitates modifying DNS data on its way from
   DNS authority servers to clients.  Moreover, DNSSEC (see RFC 4033
   [RFC4033] and RFC 4034 [RFC4034]) prevents changes to DNS data by

   By default, DNS resolvers using RPZ do not modify DNS results when
   DNSSEC signatures are available and requested by the DNS client.
   When the common "BREAK-DNSSEC" configuration setting is used, RPZ
   using resolvers ignore DNSSEC.  The result of "BREAK-DNSSEC" at DNS
   clients using DNSSEC is functionally similar to an RPZ NXDOMAIN
   policy action; the DNS client is blocked from malefactor domains.

   The policy zones might be considered sensitive, because they contain
   information about malefactors.  Like other DNS zones in most
   situations, RPZs are transferred from sources to subscribers as
   cleartext vulnerable to observation.  However, TSIG transaction
   signatures [RFC2845] SHOULD be used to authenticate and protect RPZ
   contents from modification.

   Recursive servers using RPZ are often configured to complete
   recursion even if a policy trigger provides a rewritten answer
   without needing recursion.  This impedes malefactors observing
   requests from their own authority servers from inferring whether RPZ
   is in use and whether their RRs are listed.  "qname-wait-recurse" is
   a common configuration switch that controls this behavior.

10.  References

10.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,

   [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
              DOI 10.17487/RFC1995, August 1996,

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   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, DOI 10.17487/RFC2136, April 1997,

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,

10.2.  Informative References

   [ISC-ARM]  Internet Systems Consortium, "BIND 9 Administrator
              Reference Manual,
              Bv9ARM.ch06.html#rpz", 2016.

   [ISC-RPZ]  Vixie, P. and V. Schryver, "DNS Response Policy Zones (DNS
              RPZ, Format 3),
              2010-1.txt", 2010.

   [ISC-RRL]  Vixie, P. and V. Schryver, "DNS Response Rate Limiting
              (DNS RRL),
              2012-1.txt", 2012.

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Appendix A.  Examples

   An existing data feed capable of producing an RHSBL can be trivially
   used to generate a DNS RPZ.  If the desired policy is to alias
   targeted domains to a local walled garden, then for each domain name,
   generate the following records, one for the name itself and perhaps
   also one for its sub-domains:
         *  CNAME

   If it is desirable to return NXDOMAIN for each domain (and its sub-
   domains in this example), try this:
    CNAME   .
         *  CNAME   .

   If there are specific walled gardens for mail versus everything else:
    MX      0      A
         *    MX    0
         *    A

   An extended example follows:

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         $TTL 1H
         @                 SOA LOCALHOST. (
                               1 1h 15m 30d 2h) NS LOCALHOST.

         ; QNAME policy records.
         ; There are no periods (.) after the relative owner names. CNAME .               ; NXDOMAIN policy   CNAME *.              ; NODATA policy

         ; redirect to walled garden    A
                           AAAA    2001:2::1

           ; do not rewrite OK.DOMAIN.COM (so, PASSTHRU)
        CNAME   rpz-passthru.

           ; redirect X.BZONE.DOMAIN.COM to
           *  CNAME   *

           ; rewrite all answers for 127/8 except
   CNAME   .
  CNAME   rpz-passthru.

           ; rewrite to NXDOMAIN all responses; for domains for which
           ; NS.DOMAIN.COM is an authoritative DNS server or a server
           ; for a parent) or that have an authoritative server
           ; in 2001:2::/48
    CNAME   .
           48.zz.2.2001.rpz-nsip       CNAME   .

Authors' Addresses

   Paul Vixie
   Farsight Security, Inc.


   Vernon Schryver
   Rhyolite Software


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