DELV(1) BIND 9 DELV(1)
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 <#
std-iscman-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 an-
chor 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 en-
vironments 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/re-
solv.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 ig-
nored. If an alternate key name is desired, it can be specified
using the +root option.
Note: When reading trust anchors, delv treats trust-anchors, ini-
tial-key, and static-key identically. That is, for a managed key,
it is the initial key that is trusted; RFC 5011 <https://
datatracker.ietf.org/doc/html/rfc5011.html> key management is not
supported. delv does not consult the managed-keys database main-
tained by named <#std-iscman-named>. This means that if the de-
fault 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 inter-
faces, or 0.0.0.0, or ::. An optional source port may be speci-
fied by appending #<port>
-c class
This option sets the query class for the requested data. Cur-
rently, 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 in-
creases. 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 <#
cmdoption-dig-arg-cd>.)
-m This option enables memory usage debugging.
-p port#
This option specifies a destination port to use for queries, in-
stead 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 neces-
sary 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 some-
times 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 per-
forms 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 +key-
word=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 trou-
bleshooting 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 estab-
lish a chain of trust for DNSSEC validation.
This is equivalent to setting the debug level to 1 in the "re-
solver" 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 de-
tailed dump of the queries sent by delv in the process of carry-
ing 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 "val-
idator" module of the "dnssec" logging category. Setting the sys-
temwide 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 de-
fault 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 res-
olution. 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 50.
+maxtotalqueries
This option specifies the maximum number of queries to send to
resolve a client request before giving up. The default is 200.
+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 re-
source 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 char-
acters when multiline mode is active.
+all, +noall
This option sets or clears the display options +comments, +rrcom-
ments, 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 com-
ments. 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
<#std-iscman-dig>) this does not control whether to request
DNSSEC records or to validate them. DNSSEC records are always re-
quested, and validation always occurs unless suppressed by the
use of -i or +noroot.
+root[=ROOT], +noroot
This option indicates whether to perform conventional DNSSEC val-
idation, and if so, specifies the name of a trust anchor. The de-
fault 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 re-
ceived.
+unknownformat, +nounknownformat
This option prints all RDATA in unknown RR-type presentation for-
mat (RFC 3597 <https://datatracker.ietf.org/doc/html/rfc3597
.html>). 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
SEE ALSO
dig(1) <#std-iscman-dig>, named(8) <#std-iscman-named>, RFC 4034
<https://datatracker.ietf.org/doc/html/rfc4034.html>, RFC 4035 <https://
datatracker.ietf.org/doc/html/rfc4035.html>, RFC 4431 <https://
datatracker.ietf.org/doc/html/rfc4431.html>, RFC 5074 <https://
datatracker.ietf.org/doc/html/rfc5074.html>, RFC 5155 <https://
datatracker.ietf.org/doc/html/rfc5155.html>.
Author
Internet Systems Consortium
Copyright
2026, Internet Systems Consortium
9.20.21-1~deb13u1-Debian 2026-03-13 DELV(1)
Generated by dwww version 1.16 on Mon Mar 30 03:55:08 CEST 2026.