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check_soa - Check nameservers for a domain


    check_soa [-d] [-n] [-s] [-t] [-v] domain [nameserver]


check_soa builds a list of nameservers for the zone which contains the specified domain name. The program queries each nameserver for the relevant SOA record and reports the zone serial number.

Error reports are generated for nameservers which reply with incorrect, non-authoritative or outdated information.


Fully qualified domain name to be tested. Domains within ip6.arpa or in-addr.arpa namespaces may be specified using the appropriate IP address or prefix notation.


Optional name or list of IP addresses of specific nameserver to be tested. Addresses are used in the sequence they appear in the argument list.

SOA query packets are sent to the nameservers as rapidly as the underlying hardware will allow. The program waits for a response only when it is needed for analysis. Execution time is determined by the slowest nameserver.

This perldoc(1) documentation page is displayed if the domain argument is omitted.

The program is based on the check_soa idea described by Albitz and Liu.



Turn on resolver diagnostics.


Report negative cache TTL.


Request DNSSEC resource records.


Ignore UDP datagram truncation.


Verbose output including address records for each nameserver.


check_soa example.com

Query all nameservers for the specified domain.


Query nameservers for the corresponding in-addr.arpa subdomain.

check_soa 2001:DB8::8:800:200C:417A

Query nameservers for the corresponding ip6.arpa subdomain.

check_soa 2001:DB8:0:CD30::/60

As above, for IPv6 address prefix of specified length.

check_soa z.arin.net

Query specific nameserver as above.


The program can become confused by zones which originate, or appear to originate, from more than one primary server.

The timeout code uses the perl 4-argument select() function. This is not guaranteed to work in non-Unix environments.


(c) 2003-2011 Dick Franks <rwfranks[...]acm.org>

All rights reserved.

This program is free software; you may use or redistribute it under the same terms as Perl itself.


Paul Albitz, Cricket Liu. DNS and BIND, 5th Edition. O'Reilly, 2006.

Andrews, M., Locally Served DNS Zones, RFC6303, IETF, 2011.

Andrews, M., Negative Caching of DNS Queries, RFC2308, IETF Network Working Group, 1998.

Elz, R., Bush, R., Clarifications to the DNS Specification, RFC2181, IETF Network Working Group, 1997.

Mockapetris, P., Domain Names - Implementation and Specification, RFC 1035, USC/ISI, 1987.

Larry Wall, Tom Christiansen, Jon Orwant. Programming Perl, 3rd Edition. O'Reilly, 2000.