.. Copyright (C) Internet Systems Consortium, Inc. ("ISC")
..
.. SPDX-License-Identifier: MPL-2.0
..
.. This Source Code Form is subject to the terms of the Mozilla Public
.. License, v. 2.0.  If a copy of the MPL was not distributed with this
.. file, you can obtain one at https://mozilla.org/MPL/2.0/.
..
.. See the COPYRIGHT file distributed with this work for additional
.. information regarding copyright ownership.

.. highlight: console

.. iscman:: delv
.. program:: delv
.. _man_delv:

delv - DNS lookup and validation utility
----------------------------------------

Synopsis
~~~~~~~~

:program:`delv` [@server] [ [**-4**] | [**-6**] ] [**-a** anchor-file] [**-b** address] [**-c** class] [**-d** level] [**-i**] [**-m**] [**-p** port#] [**-q** name] [**-t** type] [**-x** addr] [name] [type] [class] [queryopt...]

:program:`delv` [**-h**]

:program:`delv` [**-v**]

:program:`delv` [queryopt...] [query...]

Description
~~~~~~~~~~~

:program:`delv` is a tool for sending DNS queries and validating the results,
using the same internal resolver and validator logic as :iscman:`named`.

:program:`delv` sends to a specified name server all queries needed to
fetch and validate the requested data; this includes the original
requested query, subsequent queries to follow CNAME or DNAME chains,
queries for DNSKEY, and DS records to establish a chain of trust for
DNSSEC validation. It does not perform iterative resolution, but
simulates the behavior of a name server configured for DNSSEC validating
and forwarding.

By default, responses are validated using the built-in DNSSEC trust anchor
for the root zone ("."). Records returned by :program:`delv` are either fully
validated or were not signed. If validation fails, an explanation of the
failure is included in the output; the validation process can be traced
in detail. Because :program:`delv` does not rely on an external server to carry
out validation, it can be used to check the validity of DNS responses in
environments where local name servers may not be trustworthy.

Unless it is told to query a specific name server, :program:`delv` tries
each of the servers listed in ``/etc/resolv.conf``. If no usable server
addresses are found, :program:`delv` sends queries to the localhost
addresses (127.0.0.1 for IPv4, ::1 for IPv6).

When no command-line arguments or options are given, :program:`delv`
performs an NS query for "." (the root zone).

Simple Usage
~~~~~~~~~~~~

A typical invocation of :program:`delv` looks like:

::

    delv @server name type

where:

.. option:: server

   is the name or IP address of the name server to query. This can be an
   IPv4 address in dotted-decimal notation or an IPv6 address in
   colon-delimited notation. When the supplied ``server`` argument is a
   hostname, :program:`delv` resolves that name before querying that name
   server (note, however, that this initial lookup is *not* validated by
   DNSSEC).

   If no ``server`` argument is provided, :program:`delv` consults
   ``/etc/resolv.conf``; if an address is found there, it queries the
   name server at that address. If either of the :option:`-4` or :option:`-6`
   options is in use, then only addresses for the corresponding
   transport are tried. If no usable addresses are found, :program:`delv`
   sends queries to the localhost addresses (127.0.0.1 for IPv4, ::1
   for IPv6).

.. option:: name

   is the domain name to be looked up.

.. option:: type

   indicates what type of query is required - ANY, A, MX, etc.
   ``type`` can be any valid query type. If no ``type`` argument is
   supplied, :program:`delv` performs a lookup for an A record.

Options
~~~~~~~

.. option:: -a anchor-file

   This option specifies a file from which to read an alternate
   DNSSEC root zone trust anchor.

   By default, keys that do not match the root zone name (`.`) are
   ignored. If an alternate key name is desired, it can be
   specified using the :option:`+root` option.

   Note: When reading trust anchors, :program:`delv` treats
   ``trust-anchors``, ``initial-key``, and ``static-key`` identically. That
   is, for a managed key, it is the *initial* key that is trusted;
   :rfc:`5011` key management is not supported. :program:`delv` does not
   consult the managed-keys database maintained by :iscman:`named`. This
   means that if the default key built in to :program:`delv` is revoked,
   :program:`delv` must be updated to a newer version in order to continue
   validating.

.. option:: -b address

   This option sets the source IP address of the query to ``address``. This must be
   a valid address on one of the host's network interfaces, or ``0.0.0.0``,
   or ``::``. An optional source port may be specified by appending
   ``#<port>``

.. option:: -c class

   This option sets the query class for the requested data. Currently, only class
   "IN" is supported in :program:`delv` and any other value is ignored.

.. option:: -d level

   This option sets the systemwide debug level to ``level``. The allowed range is
   from 0 to 99. The default is 0 (no debugging). Debugging traces from
   :program:`delv` become more verbose as the debug level increases. See the
   :option:`+mtrace`, :option:`+rtrace`, and :option:`+vtrace` options below for
   additional debugging details.

.. option:: -h

   This option displays the :program:`delv` help usage output and exits.

.. option:: -i

   This option sets insecure mode, which disables internal DNSSEC validation. (Note,
   however, that this does not set the CD bit on upstream queries. If the
   server being queried is performing DNSSEC validation, then it does
   not return invalid data; this can cause :program:`delv` to time out. When it
   is necessary to examine invalid data to debug a DNSSEC problem, use
   :option:`dig +cd`.)

.. option:: -m

   This option enables memory usage debugging.

.. option:: -p port#

   This option specifies a destination port to use for queries, instead of the
   standard DNS port number 53. This option is used with a name
   server that has been configured to listen for queries on a
   non-standard port number.

.. option:: -q name

   This option sets the query name to ``name``. While the query name can be
   specified without using the :option:`-q` option, it is sometimes necessary to
   disambiguate names from types or classes (for example, when looking
   up the name "ns", which could be misinterpreted as the type NS, or
   "ch", which could be misinterpreted as class CH).

.. option:: -t type

   This option sets the query type to ``type``, which can be any valid query type
   supported in BIND 9 except for zone transfer types AXFR and IXFR. As
   with :option:`-q`, this is useful to distinguish query-name types or classes
   when they are ambiguous. It is sometimes necessary to disambiguate
   names from types.

   The default query type is "A", unless the :option:`-x` option is supplied
   to indicate a reverse lookup, in which case it is "PTR".

.. option:: -v

   This option prints the :program:`delv` version and exits.

.. option:: -x addr

   This option performs a reverse lookup, mapping an address to a name. ``addr``
   is an IPv4 address in dotted-decimal notation, or a colon-delimited
   IPv6 address. When :option:`-x` is used, there is no need to provide the
   ``name`` or ``type`` arguments; :program:`delv` automatically performs a
   lookup for a name like ``11.12.13.10.in-addr.arpa`` and sets the
   query type to PTR. IPv6 addresses are looked up using nibble format
   under the IP6.ARPA domain.

.. option:: -4

   This option forces :program:`delv` to only use IPv4.

.. option:: -6

   This option forces :program:`delv` to only use IPv6.

Query Options
~~~~~~~~~~~~~

:program:`delv` provides a number of query options which affect the way results
are displayed, and in some cases the way lookups are performed.

Each query option is identified by a keyword preceded by a plus sign
(``+``). Some keywords set or reset an option. These may be preceded by
the string ``no`` to negate the meaning of that keyword. Other keywords
assign values to options like the timeout interval. They have the form
``+keyword=value``. The query options are:

.. option:: +cdflag, +nocdflag

   This option controls whether to set the CD (checking disabled) bit in queries
   sent by :program:`delv`. This may be useful when troubleshooting DNSSEC
   problems from behind a validating resolver. A validating resolver
   blocks invalid responses, making it difficult to retrieve them
   for analysis. Setting the CD flag on queries causes the resolver
   to return invalid responses, which :program:`delv` can then validate
   internally and report the errors in detail.

.. option:: +class, +noclass

   This option controls whether to display the CLASS when printing a record. The
   default is to display the CLASS.

.. option:: +hint=FILE, +nohint

   This option specifies a filename from which to load root hints;
   this will be used to find the root name servers when name server
   mode (``delv +ns``) is in use. If the option is not specified,
   built-in root hints will be used.

.. option:: +ns, +nons

   This option toggles name server mode. When this option is in use,
   the ``delv`` process instantiates a full recursive resolver, and uses
   that to look up the requested query name and type. Turning on this
   option also activates ``+mtrace``, ``+strace`` and ``+rtrace``, so that
   every iterative query will be logged, including the full response messages
   from each authoritatve server.  These logged messages will be written
   to ``stdout`` rather than ``stderr`` as usual, so that the full trace
   can be captured more easily.

   This is intended to be similar to the behavior of ``dig +trace``, but
   because it uses the same code as ``named``, it much more accurately
   replicates the behavior of a recursive name server with a cold cache
   that is processing a recursive query.

.. option:: +qmin[=MODE], +noqmin

   When used with ``+ns``, this option enables QNAME minimization mode.
   Valid options of MODE are ``relaxed`` and ``strict``. By default,
   QNAME minimization is disabled.  If ``+qmin`` is specified but MODE
   is omitted, then ``relaxed`` mode will be used.

.. option:: +ttl, +nottl

   This option controls whether to display the TTL when printing a record. The
   default is to display the TTL.

.. option:: +rtrace, +nortrace

   This option toggles resolver fetch logging. This reports the name and
   type of each query sent by :program:`delv` in the process of carrying
   out the resolution and validation process, including the original query
   and all subsequent queries to follow CNAMEs and to establish a chain of
   trust for DNSSEC validation.

   This is equivalent to setting the debug level to 1 in the "resolver"
   logging category. Setting the systemwide debug level to 1 using the
   :option:`-d` option produces the same output, but affects other
   logging categories as well.

.. option:: +mtrace, +nomtrace

   This option toggles logging of messages received. This produces
   a detailed dump of the responses received by :program:`delv` in the
   process of carrying out the resolution and validation process.

   This is equivalent to setting the debug level to 10 for the "packets"
   module of the "resolver" logging category. Setting the systemwide
   debug level to 10 using the :option:`-d` option produces the same
   output, but affects other logging categories as well.

.. option:: +strace, +nostrace

   This option toggles logging of messages sent. This produces a detailed
   dump of the queries sent by :program:`delv` in the process of carrying
   out the resolution and validation process. Turning on this option
   also activates ``+mtrace``.

   This is equivalent to setting the debug level to 11 for the "packets"
   module of the "resolver" logging category. Setting the systemwide
   debug level to 11 using the :option:`-d` option produces the same
   output, but affects other logging categories as well.

.. option:: +vtrace, +novtrace

   This option toggles validation logging. This shows the internal process of the
   validator as it determines whether an answer is validly signed,
   unsigned, or invalid.

   This is equivalent to setting the debug level to 3 for the
   "validator" module of the "dnssec" logging category. Setting the
   systemwide debug level to 3 using the :option:`-d` option produces the
   same output, but affects other logging categories as well.

.. option:: +short, +noshort

   This option toggles between verbose and terse answers. The default is to print the answer in a
   verbose form.

.. option:: +comments, +nocomments

   This option toggles the display of comment lines in the output. The default is to
   print comments.

.. option:: +rrcomments, +norrcomments

   This option toggles the display of per-record comments in the output (for example,
   human-readable key information about DNSKEY records). The default is
   to print per-record comments.

.. option:: +crypto, +nocrypto

   This option toggles the display of cryptographic fields in DNSSEC records. The
   contents of these fields are unnecessary to debug most DNSSEC
   validation failures and removing them makes it easier to see the
   common failures. The default is to display the fields. When omitted,
   they are replaced by the string ``[omitted]`` or, in the DNSKEY case, the
   key ID is displayed as the replacement, e.g. ``[ key id = value ]``.

.. option:: +restarts

   When name server mode (``delv +ns``) is in use, this option sets the
   maximum number of CNAME queries to follow before terminating resolution.
   This prevents ``delv`` from hanging in the event of a CNAME loop.
   The default is 11.

.. option:: +maxqueries

   This option specifies the maximum number of queries to send to resolve
   a name before giving up. The default is 50.

.. option:: +maxtotalqueries

   This option specifies the maximum number of queries to send to resolve
   a client request before giving up. The default is 200.

.. option:: +trust, +notrust

   This option controls whether to display the trust level when printing a record.
   The default is to display the trust level.

.. option:: +split[=W], +nosplit

   This option splits long hex- or base64-formatted fields in resource records into
   chunks of ``W`` characters (where ``W`` is rounded up to the nearest
   multiple of 4). ``+nosplit`` or ``+split=0`` causes fields not to be
   split at all. The default is 56 characters, or 44 characters when
   multiline mode is active.

.. option:: +all, +noall

   This option sets or clears the display options :option:`+comments`,
   :option:`+rrcomments`, and :option:`+trust` as a group.

.. option:: +multiline, +nomultiline

   This option prints long records (such as RRSIG, DNSKEY, and SOA records) in a
   verbose multi-line format with human-readable comments. The default
   is to print each record on a single line, to facilitate machine
   parsing of the :program:`delv` output.

.. option:: +dnssec, +nodnssec

   This option indicates whether to display RRSIG records in the :program:`delv` output.
   The default is to do so. Note that (unlike in :iscman:`dig`) this does
   *not* control whether to request DNSSEC records or to
   validate them. DNSSEC records are always requested, and validation
   always occurs unless suppressed by the use of :option:`-i` or
   :option:`+noroot`.

.. option:: +root[=ROOT], +noroot

   This option indicates whether to perform conventional DNSSEC validation, and if so,
   specifies the name of a trust anchor. The default is to validate using a
   trust anchor of "." (the root zone), for which there is a built-in key. If
   specifying a different trust anchor, then :option:`-a` must be used to specify a
   file containing the key.

.. option:: +tcp, +notcp

   This option controls whether to use TCP when sending queries. The default is to
   use UDP unless a truncated response has been received.

.. option:: +unknownformat, +nounknownformat

   This option prints all RDATA in unknown RR-type presentation format (:rfc:`3597`).
   The default is to print RDATA for known types in the type's
   presentation format.

.. option:: +yaml, +noyaml

   This option prints response data in YAML format.

Files
~~~~~

``/etc/resolv.conf``

See Also
~~~~~~~~

:iscman:`dig(1) <dig>`, :iscman:`named(8) <named>`, :rfc:`4034`, :rfc:`4035`, :rfc:`4431`, :rfc:`5074`, :rfc:`5155`.
