General Network Troubleshooting Tips

One of the first signs of trouble on a network is a loss of communications by one or more hosts. If a host does not to come up at all the first time that the host is added to the network, the problem might be in one of the configuration files. The problem might also be a faulty network interface card. If a single host suddenly develops a problem, the network interface might be the cause. If the hosts on a network can communicate with each other but not with other networks, the problem could lie with the router. Or, the problem could be in another network.

You can use the ifconfig command to obtain information on network interfaces. Use the netstat command to display routing tables and protocol statistics. Third-party network diagnostic programs provide a number of troubleshooting tools. Refer to third-party documentation for information.

Less obvious are the causes of problems that degrade performance on the network. For example, you can use tools such as ping to quantify problems such as the loss of packets by a host.

Running Basic Diagnostic Checks

If the network has problems, you can run a series of software checks to diagnose and fix basic, software-related problems.

How to Perform Basic Network Software Checking

On the local system, assume the Network Management role or become superuser.
Roles contain authorizations and privileged commands. For more information about roles, see Configuring RBAC (Task Map) in System Administration Guide: Security Services.
Use the netstat command to display network information.
For syntax and information about the netstat command, refer to Monitoring Network Status With the netstat Command and the netstat(1M) man page.
Check the hosts database to ensure that the entries are correct and current.
For information about the /etc/inet/hosts database, refer to hosts Database and the hosts(4) man page.
If you are running the Reverse Address Resolution Protocol (RARP), check the Ethernet addresses in the ethers database to ensure that the entries are correct and current.
Try to connect to the local host by using the telnet command.
For syntax and information about telnet, refer to the telnet(1) man page.
Ensure that the network daemon inetd is running.
# ps -ef | grep inetd
The following output verifies that the inetd daemon is running:
```
root 57 1 0 Apr 04 ? 3:19 /usr/sbin/inetd -s
```
If IPv6 is enabled on your network, verify that the IPv6 daemon in.ndpd is running:
```
# ps -ef | grep in.ndpd
```
The following output verifies that the in.ndpd daemon is running:
```
root 123  1 0  Oct 27 ?  0:03 /usr/lib/inet/in.ndpd
```