Domain Name Service (DNS) is a system which translates the meaningful Hostnames and Domain Names into valid IP Addresses. A DNS Client or a Resolver is a host or a network device which queries the DNS servers for various resource records like the IP Address for a host like a Mail Server.
The nscd daemon is a caching daemon in Sun Solaris. It provides caching services for hosts,passwd,group,ipnodes databases using various nameservice lookups like hosts file, DNS, NIS,NIS+ and more. Each cache has a separate time-to-live for its data and modifying the local database like /etc/hosts invalidates that cache within ten seconds. nscd doesn’t cache /etc/shadow (contains encrypted passwords for /etc/passwd) file simple for security reasons as anyone would understand.
As nscd daemon provides caching service, it is necessary when you run a name service like DNS, NIS or NIS+ in your network. The configuration of nscd daemon can customised using the /etc/nscd.conf file and it is important more from a security point of view where you can control what is and how is cached on your solaris server.
It may be sometime required to flush your DNS Cache mostly when trying to troubleshoot a problem with your name service or when there was an invalid DNS entry after a server outage. The possible solution to clear these cached invalid entries or to wait till the record expires based on its TTL (Time To Live)