Testing Network Connectivity

To make sure your network connections are configured and behaving properly, do these tasks:

•	Confirm that your computer has the appropriate settings for DNS servers, the correct hostname, and an available IP address with the proper subnet mask (show hosts); the proper default gateway (show ip default-gateway).

•	Check network interfaces (show interfaces). Make sure the links are up, the addresses are correct, default routes are set correctly (show ip route). Check cable connectivity.

•	Check ARP tables (show arp).

•	Check DNS /hostnames configurations (show hosts).

•	Check that applications like SSH, and Firefox are working.

•	Test connections to remote servers; use ping (Ctrl+c to stop ping):

a.	Ping the loopback address (by using the ping 127.0.0.1 command) to verify that TCP/IP is installed and working correctly on the local computer.

b.	Ping the local computer IP address to verify it was added to the network correctly.

c.	Ping the IP address of the default gateway to verify that the gateway is functional and it is possible to connect to a local host on the local network.

d.	Ping the IP address of another remote host to verify that you can communicate through a router.

•	Check the network path to a destination with traceroute:

a.	At the command prompt, type traceroute <IP_address_of_remote_network_host>, and then press ENTER.

b.	Examine the results to determine the length of time that the packet took to reach each network segment and the point at which the connection may stop working.

 

Table 20 TCP/IP Diagnostic Utilities

Utility	Used to...
show arp	View the ARP (address resolution protocol) table on the local computer to detect invalid entries.
show hosts	View hostname, DNS configuration, and static host mappings
show ip {default-gateway | route}	Display current TCP/IP network configuration values
ping	Verify whether TCP/IP is configured correctly and that a remote TCP/IP system is available
traceroute	Check the route to a remote system