To totally unlock this section you need to Log-in
Login
You might need to check the status of your DNS records for many reasons. For example, you might need to verify that any updates are correct or to troubleshoot issues accessing a particular service. Windows has a built-in tool for checking your DNS records, nslookup.
To access nslookup open up a command prompt window. Go to Start > All Programs > Accessories > Command Prompt.
Check for a record
To check for a specific record you need to specify the nslookup command, the record type — for example, A, MX, or TXT — and the host name you want to check. The following example shows how to check for any A records for example.com:
C:\Users\Administrator>nslookup -type=A example.com Server: dns1.example.com> Address: 84.118.131.60 Non-authoritative answer: Name: example.com Address: 212.10.11.34
The first two lines of output specify the server to which the request was directed which is the default server that your system uses for DNS name resolution. The second section, which specifies a non-authoritative answer, gives the name of the record and the corresponding IP address. The answer is non-authoritative because the answer comes from a server, dns1.example.com in this case, that is not the root source for those records.
Get an authoritative answer
To get an authoritative answer you need to go to the source. You can do this by specifying the authoritative name server at the end of the request.
Use the -type=soa option to tell nslookup to display the authoritative (primary) name server.
C:\Users\Administrator>nslookup -type=soa rackspace.co.uk Server: dns1.example.com> Address: 84.118.131.60 Non-authoritative answer: example.com primary name server = dns.example.com responsible mail addr = hostmaster.example.com serial = 1415913000 refresh = 3600 (1 hour) retry = 300 (5 mins) expire = 1814400 (21 days) default TTL = 300 (5 mins) dns.example.com internet address = 93.20.33.11
The address labeled primary name server is the DNS authority for the domain.
If you add the address of the authoritative name server (dns.example.com) to the first command, the record is now checked against that name server.
C:\Users\Administrator>nslookup -type=A example.com dns.example.com Server: dns.example.com Address: 69.20.95.4 Name: example.com Address: 212.64.133.165
Check when a cached record will expire
DNS uses caching, which reduces the load on authoritative name servers but means that sometimes records can be out of date. If the authoritative and non-authoritative answers differ, you will have a cached response from the resolver name server you are using. The length of time that a record is cached depends on its time-to-live (TTL) value. This is a number specified in seconds.
To see how long a record is cached, include the debug option, as shown in the following example:
C:\Users\Administrator>nslookup -type=A -debug example.com ------------ Got answer: HEADER: opcode = QUERY, id = 1, rcode = NOERROR header flags: response, want recursion, recursion avail. questions = 1, answers = 1, authority records = 2, additional = 2 QUESTIONS: 80.151.138.83.in-addr.arpa, type = PTR, class = IN ANSWERS: -> 80.151.138.83.in-addr.arpa name = dns1.rackspace.com ttl = 2466 (41 mins 6 secs) AUTHORITY RECORDS: -> 151.138.83.in-addr.arpa nameserver = dns-au.example.com ttl = 2466 (41 mins 6 secs) -> 151.138.83.in-addr.arpa nameserver = dns.example.com ttl = 2466 (41 mins 6 secs) ADDITIONAL RECORDS: -> dns.example.com internet address = 69.20.95.4 ttl = 12982 (3 hours 36 mins 22 secs) -> dns-au.example.com.rackspace.com internet address = 65.61.188.4 ttl = 12985 (3 hours 36 mins 25 secs) ------------ Server: dns1.example.com Address: 83.138.151.80 ------------ Got answer: HEADER: opcode = QUERY, id = 2, rcode = NOERROR header flags: response, want recursion, recursion avail. questions = 1, answers = 1, authority records = 2, additional = 2 QUESTIONS: example.com, type = A, class = IN ANSWERS: -> example internet address = 212.64.133.165 ttl = 279 (4 mins 39 secs) AUTHORITY RECORDS: -> example nameserver = dns.example.com ttl = 17465 (4 hours 51 mins 5 secs) -> rackspace.co.uk nameserver = dns-au.example.com ttl = 17465 (4 hours 51 mins 5 secs) ADDITIONAL RECORDS: -> dns.example.com internet address = 69.20.95.4 ttl = 15754 (4 hours 22 mins 34 secs) -> dns-au.example.com internet address = 65.61.188.4 ttl = 15727 (4 hours 22 mins 7 secs) ------------ Non-authoritative answer: Name: example Address: 212.64.133.165
The first Got answer section of this example is used to get the hostname of the server from which you are requesting the A record from, in this case dns1.example.com.
- The second Got answer section relates to your actual request.
- The HEADER section contains details about the type of request and its success.
- The QUESTIONS section shows that the request was for A records for example.com.
- he ANSWERS section displays one record with an IP address of 212.64.133.165 and a TTL of 279 seconds (4 minutes 39 seconds).
- The AUTHORITY RECORDS section specifies the name servers that correspond to the domain.
- The ADDITIONAL RECORDS section lists A records for the name servers listed in the authority records section.
So from this response, you can see that the name server being used by the client computer will reuse the same A record for example.com for the next 4 minutes and 39 seconds. If you were to run the same command on the authoritative name server you would see what the current maximum TTL for the record is.