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DELV(1) BIND 9 DELV(1)
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delv - DNS lookup and validation utility
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 [queryopt...] [query...]
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 valida-
tion. It does not perform iterative resolution, but simulates the
behavior of a name server configured for DNSSEC validating and forward-
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 trustwor-
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).
A typical invocation of delv looks like:
delv @server name type
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
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 sup-
plied, delv performs a lookup for an A record.
This option specifies a file from which to read DNSSEC trust
anchors. The default is /etc/bind.keys, which is included with
BIND 9 and contains one or more trust anchors for the root zone
Keys that do not match the root zone name are ignored. An alter-
nate key name can be specified using the +root=NAME options.
Note: When reading the trust anchor file, 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, which means that if
either of the keys in /etc/bind.keys is revoked and rolled over,
/etc/bind.keys must be updated to use DNSSEC validation in delv.
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>
This option sets the query class for the requested data. Cur-
rently, only class "IN" is supported in delv and any other value
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.
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.
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 exam-
ple, when looking up the name "ns", which could be misinter-
preted as the type NS, or "ch", which could be misinterpreted as
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.
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 126.96.36.199.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.
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:
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 diffi-
cult 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
This option controls whether to display the CLASS when printing
a record. The default is to display the CLASS.
This option controls whether to display the TTL when printing a
record. The default is to display the TTL.
This option toggles resolver fetch logging. This reports the
name and type of each query sent by delv in the process of car-
rying 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.
This option toggles message logging. This produces a detailed
dump of the responses received by delv in the process of carry-
ing 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.
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
systemwide debug level to 3 using the -d option produces the
same output, but affects other logging categories as well.
This option toggles between verbose and terse answers. The
default is to print the answer in a verbose form.
This option toggles the display of comment lines in the output.
The default is to print comments.
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.
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 replace-
ment, e.g. [ key id = value ].
This option controls whether to display the trust level when
printing a record. The default is to display the trust level.
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.
This option sets or clears the display options +[no]comments,
+[no]rrcomments, and +[no]trust as a group.
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.
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 valida-
tion always occurs unless suppressed by the use of -i or
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 dif-
ferent trust anchor, then -a must be used to specify a file con-
taining the key.
This option controls whether to use TCP when sending queries.
The default is to use UDP unless a truncated response has been
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.
This option prints response data in YAML format.
dig(1), named(8), RFC 4034, RFC 4035, RFC 4431, RFC 5074, RFC 5155.
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