The link between a LAN and a WAN includes several components that could cause a link to fail, including cables, connections, NICs, gateways, and the ISP. A common problem is the configuration of hardware and software. Areas where configuration issues are common include the DHCP server, email server and clients, the hosts file, NICs, routers and switches, VLANs, default gateways, and firewalls.
In many cases, the messages that are displayed characterize a problem, but not necessarily its cause. These include resource unavailable, destination host unreachable, unknown host, failure of service provider, and cannot resolve hostname/FQDN.
Some of the network problem troubleshooting tools available are ping, tracert/traceroute, ipconfig, nslookup, net use, mount, nbtstat, and netstat.
