One of the first signs of trouble on the network is a loss of communications by one or more hosts. If a host refuses 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 program to obtain information on network interfaces and netstat to display routing tables and protocol statistics. Third-party network diagnostic programs provide a number of troubleshooting utilities. Refer to third-party documentation for information.