Ubuntu Manpage: delv - DNS lookup and validation utility

Provided by: bind9-dnsutils_9.20.4-3ubuntu1.2_amd64

NAME

       delv - DNS lookup and validation utility

SYNOPSIS

       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...]

       delv [-h]

       delv [-v]

       delv [queryopt...] [query...]

DESCRIPTION

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

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 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 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, delv tries each of the servers listed in
/etc/resolv.conf. If no usable server addresses are found, 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, delv performs an NS query for "." (the root zone).

SIMPLE USAGE

       A typical invocation of delv looks like:

          delv @server name type

       where:

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

       name   is the domain name to be looked up.

       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, delv performs a lookup for an A record.

OPTIONS

-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 +root option.

Note: When reading trust anchors, 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. delv does not consult the managed-keys database maintained by named.
This means that if the default key built in to delv is revoked, delv must be updated to a newer
version in order to continue validating.

-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>

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

-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 delv become more verbose as the debug level
increases. See the +mtrace, +rtrace, and +vtrace options below for additional debugging details.

-h This option displays the delv help usage output and exits.

-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 delv to time out. When it is
necessary to examine invalid data to debug a DNSSEC problem, use dig +cd.)

-m This option enables memory usage debugging.

-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.

-q name
This option sets the query name to name. While the query name can be specified without using the
-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).

-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 -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 -x option is supplied to indicate a reverse lookup, in
which case it is "PTR".

-v This option prints the delv version and exits.

-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 -x is used, there is no need to
provide the name or type arguments; 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.

-4 This option forces delv to only use IPv4.

-6 This option forces delv to only use IPv6.

QUERY OPTIONS

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:

+cdflag, +nocdflag
This option controls whether to set the CD (checking disabled) bit in queries sent by 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 delv can then validate
internally and report the errors in detail.

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

+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.

+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.

+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.

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

+rtrace, +nortrace
This option toggles resolver fetch logging. This reports the name and type of each query sent by
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 -d option produces the same output, but affects other
logging categories as well.

+mtrace, +nomtrace
This option toggles logging of messages received. This produces a detailed dump of the responses
received by 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 -d option produces the same
output, but affects other logging categories as well.

+strace, +nostrace
This option toggles logging of messages sent. This produces a detailed dump of the queries sent by
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 -d option produces the same
output, but affects other logging categories as well.

+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 -d option produces the same
output, but affects other logging categories as well.

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

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

+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.

+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 ].

+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.

+maxqueries
This option specifies the maximum number of queries to send to resolve a name before giving up.
The default is 32.

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

+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.

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

+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 delv output.

+dnssec, +nodnssec
This option indicates whether to display RRSIG records in the delv output. The default is to do
so. Note that (unlike in 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 -i or +noroot.

+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 -a must be used to
specify a file containing the key.

+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.

+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.

+yaml, +noyaml
This option prints response data in YAML format.

FILES

       /etc/resolv.conf

AUTHOR

       Internet Systems Consortium

COPYRIGHT

       2025, Internet Systems Consortium

9.20.4-3ubuntu1.2-Ubuntu                           2024-12-03                                            DELV(1)