Other Basic Tools

traceroute
 

enables the network manager to discover the route taken by IP datagrams in travelling to a remote host. Read the "man" page for traceroute before using it in "regular operations". As for ping, the manual states:

This program is intended for use in network testing, measurement and management. It should be used primarily for manual fault isolation. Because of the load it could impose on the network, it is unwise to use traceroute during normal operations or from automated scripts.

netstat
 

gives information about the UNIX kernel data structures associated with TCP/IP. For example, netstat -r prints the kernel routing table, netstat -a reports on all current TCP activity and netstat -C gives a continually updated real-time display of most network-related parameters. netstat is a very useful piece of software.
 

arp
 

This command reports on all current Address Resolution Protocol (IP to MAC address mapping) information, and allows the network manager to "hard-wire" an ARP entry if desired. Can be very useful where Proxy-ARP is in use, or where "ARP spoofing is suspected.
 

nslookup, dig
 

useful for checking DNS (Name Service) operation. Note that if DNS is not operational, other tools may still be usable with dotted IP addresses instead of names.
 

telnet
 

useful for checking operation of the TCP sub-system. In addition, many network devices (eg, most routers) support telnet connection by the network manager to check loads, error rates, etc. Always remember that telnet passwords cross the network in plain text.