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 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).
A typical invocation of delv looks like:
delv @server name type
- 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).
- is the domain name to be looked up.
- 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.
- -a anchor-file
- This option specifies a file from which to read DNSSEC trust anchors. The
default is /etc/bind/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 alternate 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/bind.keys is revoked and rolled over, /etc/bind/bind.keys must be updated to use DNSSEC validation in delv.
- -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.
- This option displays the delv help usage output and exits.
- 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.)
- 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".
- 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 184.108.40.206.in-addr.arpa and sets the query type to PTR. IPv6 addresses are looked up using nibble format under the IP6.ARPA domain.
- This option forces delv to only use IPv4.
- 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 +keyword=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 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.
- 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 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
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 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.
- 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.
- 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 replacement, 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 comments. 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 validation always occurs unless suppressed by the use of -i or +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.
- This option controls whether to use TCP when sending queries. The default is to use UDP unless a truncated response has been received.
- 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.
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