Suppose that the command netstat -a hangs for a long time without producing output. You might suspect:

A.
a problem with NFS

B.
a problem with DNS

C.
a problem with NIS

D.
a problem with routing

E.
that the netstat daemon has crashed

Explanation/Reference:
If the -n, –numeric option is not specified netstat tries to resolve all ip addresses into hostnames; hostnames are provided by a nameserver (or locally using /etc/hosts). The default timeout for a nameserver query is 5 seconds, so a long waiting time would indicate the DNS is not responding (or configured incorrectly).