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Without any arguments it queries the DNS root zone. dig supports Internationalized domain name (IDN) queries. dig is a component of the domain name server software suite BIND. dig supersedes in functionality older tools, such as nslookup and the program host; however, the older tools are still used in complementary fashion.
Excluded from consideration are single-feature DNS tools (such as proxies, filters, and firewalls) and redistributions of servers listed here (many products repackage BIND, for instance, with proprietary user interfaces). DNS servers are grouped into several categories of specialization of servicing domain name system queries.
nslookup operates in interactive or non-interactive mode. When used interactively by invoking it without arguments or when the first argument is - (minus sign) and the second argument is a hostname or Internet address of a name server, the user issues parameter configurations or requests when presented with the nslookup prompt (>).
For example, to do a reverse lookup of the IP address 8.8.4.4 the PTR record for the domain name 4.4.8.8.in-addr.arpa would be looked up, and found to point to dns.google. If the A record for dns.google in turn pointed back to 8.8.4.4 then it would be said to be forward-confirmed.
A DNS name server is a server that stores the DNS records for a domain; a DNS name server responds with answers to queries against its database. The most common types of records stored in the DNS database are for start of authority ( SOA ), IP addresses ( A and AAAA ), SMTP mail exchangers (MX), name servers (NS), pointers for reverse DNS ...
That is, the reverse DNS might verify, but it will usually be part of another domain than the claimed domain name. Using an ISP's mail server as a relay may solve the reverse DNS problem, because the requirement is the forward and reverse lookup for the sending relay have to match, it does not have to be related to the from-field or sending ...
However, most modern WHOIS tools implement command line flags or options, such as the -h option to access a specific server host, but default servers are preconfigured. Additional options may allow control of the port number to connect on, displaying additional debugging data, or changing recursion/referral behavior.
dnsmasq caches DNS records, reducing the load on upstream nameservers and improving performance, and can be configured to automatically pick up the addresses of its upstream servers. dnsmasq accepts DNS queries and either answers them from a small, local cache or forwards them to a real, recursive DNS server.