The status of network interfaces may be viewed at Status > Interfaces. In the first part of Figure Interface Status, a DHCP WAN connection has been made and the IPv4 and IPv6 address, DNS, etc have been obtained automatically. The MAC address, media type, in/out packets, errors, and collisions for the network interface are all visible. Dynamic connection types like PPPoE and PPTP have a Disconnect button when connected and a Connect button when offline. Interfaces obtaining an IP address from DHCP have a Release button when there is an active lease, and a Renew button when there is not.
In the lower part of the image, the LAN connection is visible. Since this is a normal interface with a static IP address, only the usual set of items are shown.
If an interface status indicates “no carrier” then it typically means that the cable is not plugged in or the device on the other end is malfunctioning in some way. If any errors are shown, they are typically physical in nature: cabling or port errors. The most common suspect is cables, and they are easy and cheap to replace. In some circumstances errors and collisions may appear due to a link speed or duplex mismatch. See Interface Configuration for more about setting the speed and duplex of an interface.