Response Policy Zones (RPZ)

Response Policy Zone is an open standard developed by Paul Vixie (ISC and Farsight) and Vernon Schryver (Rhyolite), to modify DNS responses based on a policy loaded via a zonefile.

Frequently, Response Policy Zones get to be very large and change quickly, so it is customary to update them over IXFR. It allows the use of third-party feeds, and near real-time policy updates.

If multiple RPZs are loaded, they get consulted in the order they were defined in. It is however possible from Lua to make queries skip specific Response Policy Zones.

Configuring RPZ

An RPZ can be loaded from file or slaved from a master. To load from file, use for example:

rpzFile("dblfilename", {defpol=Policy.Custom, defcontent="badserver.example.com"})

To slave from a master and start IXFR to get updates, use for example:

rpzMaster("192.0.2.4", "policy.rpz", {defpol=Policy.Drop})

In this example, ‘policy.rpz’ denotes the name of the zone to query for.

As of .. versionchanged:: 4.2.0: you can add IP blocks into the rpzMaster as:

rpzMaster({“192.0.2.4”,”192.0.2.5”}, “policy.rpz”, {defpol=Policy.Drop})
rpzFile(filename, settings)

Load an RPZ from disk.

Parameters:
  • filename (str) – The filename to load
  • settings ({}) – A table to settings, see below
rpzMaster(address, name, settings)

Changed in version 4.2.0:: The first parameter can be a list of addresses.

Load an RPZ from AXFR and keep retrieving with IXFR.

Parameters:
  • address (str) – The IP address to transfer the RPZ from. Also accepts a list of addresses since 4.2.0 in which case they will be tried one after another in the submitted order until a response is obtained.
  • name (str) – The name of this RPZ
  • settings ({}) – A table to settings, see below

RPZ settings

These options can be set in the settings of both rpzMaster() and rpzFile().

defcontent

CNAME field to return in case of defpol=Policy.Custom

defttl

the TTL of the CNAME field to be synthesized for the default policy. The default is to use the zone’s TTL,

maxTTL

The maximum TTL value of the synthesized records, overriding a higher value from defttl or the zone. Default is unlimited.

policyName

The name logged as ‘appliedPolicy’ in protobuf messages when this policy is applied.

zoneSizeHint

An indication of the number of expected entries in the zone, speeding up the loading of huge zones by reserving space in advance.

Extra settings for rpzMaster

In addition to the settings above the settings for rpzMaster() may contain:

tsigname

The name of the TSIG key to authenticate to the server. When this is set, tsigalgo and tsigsecret must also be set.

tsigalgo

The name of the TSIG algorithm (like ‘hmac-md5’) used

tsigsecret

Base64 encoded TSIG secret

refresh

An integer describing the interval between checks for updates. By default, the RPZ zone’s default is used

maxReceivedMBytes

The maximum size in megabytes of an AXFR/IXFR update, to prevent resource exhaustion. The default value of 0 means no restriction.

localAddress

The source IP address to use when transferring the RPZ. When unset, query-local-address and query-local-address6 are used.

axfrTimeout

New in version 4.1.2: Before 4.1.2, the timeout was fixed on 10 seconds.

The timeout in seconds of the total initial AXFR transaction. 20 by default.

dumpFile

New in version 4.2.0.

A path to a file where the recursor will dump the latest version of the RPZ zone after each successful update. This can be used to keep track of changes in the RPZ zone, or to speed up the initial loading of the zone via the seedFile parameter. The format of the generated zone file is the same than the one used with rpzFile(), and can also be generated via:

rec_control dump-rpz zone-name output-file

seedFile

New in version 4.2.0.

A path to a file containing an existing dump of the RPZ zone. The recursor will try to load the zone from this file on startup, then immediately do an IXFR to retrieve any updates. If the file does not exist or is not valid, the normal process of doing a full AXFR will be used instead. This option allows a faster startup by loading an existing zone from a file instead of retrieving it from the network, then retrieving only the needed updates via IXFR. The format of the zone file is the same than the one used with rpzFile(), and can for example be generated via:

rec_control dump-rpz zone-name output-file

It is also possible to use the dumpFile parameter in order to dump the latest version of the RPZ zone after each update.

Policy Actions

If no settings are included, the RPZ is taken literally with no overrides applied. Several Policy Actions exist

Policy.Custom

Will return a NoError, CNAME answer with the value specified with defcontent, when looking up the result of this CNAME, RPZ is not taken into account.

Policy.Drop

Will simply cause the query to be dropped.

Policy.NoAction

Will continue normal processing of the query.

Policy.NODATA

Will return a NoError response with no value in the answer section.

Policy.NXDOMAIN

Will return a response with a NXDomain rcode.

Policy.Truncate

will return a NoError, no answer, truncated response over UDP. Normal processing will continue over TCP