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.

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 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 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

SEE ALSO

dig(1), named(8), RFC 4034, RFC 4035, RFC 4431, RFC 5074, RFC 5155.

AUTHOR
Internet Systems Consortium

COPYRIGHT
2025, Internet Systems Consortium