Following are the important physical interfaces in a Cisco Router.
• Ethernet - Ethernet is typically Ethernet IEEE 802.3 standard based physical interface, which operates at 10 Mbps speed. The media standard used is 10BaseT.
• Fast Ethernet - Fast Ethernet is typically Ethernet IEEE 802.3u standard based physical interface which operates at 100 Mbps speed. The media standard used is 100BaseT.
• Gigabit Ethernet - Gigabit Ethernet is typically Ethernet IEEE 802.3ab standard based physical interface which operates at 1000 Mbps speed. The media standard used is1000BASE-T
• Serial: Serial interfaces are typically used for WAN connections from ISP (Internet Service Providers) for connectivity types like Frame Relay, T1, T3, etc
• FDDI Fiber Distributed Data Interface. - FDDI networks operates at 100 Mbps speed and uses a token-passing mechanism to prevent collisions.
• Token Ring - Token Ring interfaces can operate at either 4 Mbps or 16 Mbps. In Token Ring networks a token is passed around the network (configured in ring topology), allowing the owner of the token to transmit a frame, to avoid collision.Token Ring networks vanished from networking industry long way back. New Cisco routers do not have a Token Ring interface.
Note : Only 10Mbps Ethernet interface has a name "Ethernet" in a Cisco Router. A 100Mbps Ethernet interface is called a "FastEthernet" interface and a 1000Mbps Ethernet interface is called a "GigabitEthernet" interface.
Virtual interfaces are also available in a Cisco Router. Examples of virtual interfaces are Loopback interface and Null interface.