The nslookup utility is used to resolve either hostnames to IP addresses or IP addresses to hostnames.

NSLookup Help File:

#pragma ident   "@(#)nslookup.help      1.6     96/09/12 SMI"
 
Commands:       (identifiers are shown in uppercase, [] means optional)
NAME            - print info about the host/domain NAME using default server
NAME1 NAME2     - as above, but use NAME2 as server
help or ?       - print info on common commands; see nslookup(1) for details
set OPTION      - set an option
    all         - print options, current server and host
    [no]debug   - print debugging information
    [no]d2      - print exhaustive debugging information
    [no]defname - append domain name to each query
    [no]recurse - ask for recursive answer to query
    [no]vc      - always use a virtual circuit
    domain=NAME - set default domain name to NAME
    srchlist=N1[/N2/.../N6] - set domain to N1 and search list to N1,N2, etc.
    root=NAME   - set root server to NAME
    retry=X     - set number of retries to X
    timeout=X   - set initial time-out interval to X seconds
    querytype=X - set query type, e.g., A,ANY,CNAME,HINFO,MX,PX,NS,PTR,SOA,TXT,W
KS
    port=X      - set port number to send query on
    type=X      - synonym for querytype
    class=X     - set query class to one of IN (Internet), CHAOS, HESIOD or ANY
server NAME     - set default server to NAME, using current default server
lserver NAME    - set default server to NAME, using initial server
finger [USER]   - finger the optional USER at the current default host
root            - set current default server to the root
ls [opt] DOMAIN [> FILE] - list addresses in DOMAIN (optional: output to FILE)
    -a          -  list canonical names and aliases
    -h          -  list HINFO (CPU type and operating system)
    -s          -  list well-known services
    -d          -  list all records
    -t TYPE     -  list records of the given type (e.g., A,CNAME,MX, etc.)
view FILE       - sort an 'ls' output file and view it with more
exit            - exit the program, ^D also exits