16.6. Communications Commands (Revision #1)

Certain of the following commands find use in network data transfer and analysis, as well as in chasing spammers.

Information and Statistics

host

Searches for information about an Internet host by name or IP address, using DNS.

bash$ host surfacemail.com
surfacemail.com. has address 202.92.42.236

ipcalc

Displays IP information for a host. With the -h option, ipcalc does a reverse DNS lookup, finding the name of the host (server) from the IP address.

bash$ ipcalc -h 202.92.42.236
HOSTNAME=surfacemail.com

nslookup

Do an Internet "name server lookup" on a host by IP address. This is essentially equivalent to  ipcalc  -h or dig -x . The command may be run either interactively or noninteractively, i.e., from within a sc ript.

The nslookup command has allegedly been "deprecated," but it is still useful.

bash$ nslookup -sil 66.97.104.180
nslookup kuhleersparnis.ch
Server:         135.116.137.2
Address:        135.116.137.2#53

Non-authoritative answer:
Name:   kuhleersparnis.ch

dig

Domain Information Groper. Similar to nslookup, dig does an Internet name server lookup on a host. May be run from the command-line or from within a script.

Some interesting options to dig are +time=N for setting a query timeout to N seconds, +nofail for continuing to query servers until a reply is received, and -x for doing a reverse address lookup.

Compare the output of   dig -x   with  ipcalc -h  and nslookup.