Which of the following commands helps you determine the Layer 1 and Layer 2 up/down status of a Cisco
interface?
A.
show controllers
B.
show running-config
C.
show interfaces trunk
D.
show interfaces
Explanation:
The show interfaces command displays the Layer 1 and Layer 2 operational status of an interface, along with
other information.
Of interest in this output is the information contained on line 14 (also shown below). The figures for Runts and
Giants (packets that are either too large or too small) indicate that collisions are occurring or that the NIC is
malfunctioning:
Received 354125 broadcasts, 586 runts, 705 giants
As a part of troubleshooting this increase in collisions, you can also identify the speed of the interface by
reading line 4, which says the bandwidth is 10000 Kbit, indicating a FastEthernet interface.
MTU 1500 bytes, BW 10000 Kbit, DLY 100000 usec, rely 255/255, load 1/255
You can also specify a particular interface for which information should be displayed, as shown below:
Router# show interfaces ethernet 0/0
Ethernet0/0 is administratively down, line protocol is downHardware is AmdP2, address is 0003.e39b.9220 (via 0003.e39b.9220)
Internet address is 10.1.0.254/16
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 04:00:00
<<output omitted>>
The sample output indicates that interface Ethernet 0/0 is in an administratively down, line protocol is down
state. The first statement indicates the Layer 1 (Physical) status, while the second statement indicates the
Layer 2 (Data Link) status of the interface. A status of administratively down always indicates that the interface
is in a shutdown state; the interface can be activated by executing the command no shutdown. This command
also indicates the configured bandwidth of the interface (10000 Kbit in this case).
The following lines of information concern the Physical layer:
Hardware is AmdP2, address is 0003.e39b.9220 (via 0003.e39b.9220)
Ethernet0/0 is administratively down, line protocol is down
This output indicates that the link has not been enabled. There are other combinations of up and down states
that can indicate other conditions. For example, the following indicates the link is functioning:
Ethernet0/0 is up, line protocol is up
The output below indicates a problem at the other end of the link, perhaps meaning that the interface on the
other end has not been enabled or that the port to which it is connected has been disabled.
Ethernet0/0 is up, line protocol is down (not connect)
The following lines of information concern the Data Link layer:
Encapsulation ARPA
line protocol is down
The show controllers command provides Layer 1 information only, including the type of cable detected (DTE/
DCE) on a serial interface.
The show running-config command displays the current active configuration of the router, but does not indicate
the operational status of its interfaces.
The show interfaces trunk command will not show the Layer 1 and Layer 2 up/down status of a Cisco interface.
It will show all interfaces configured to be trunks. This command is very useful when you need to locate trunk
interfaces on a switch with which you are not familiar. In the output of the command below, the three trunking
interfaces are the Fa0/3, Fa0/9, and Fa0/12 interfaces.
Objective:
LAN Switching Fundamentals
Sub-Objective:
Troubleshoot interface and cable issues (collisions, errors, duplex, speed)References:
Cisco > Catalyst 6500 Series Cisco IOS Command Reference, 12.1 E > show bootvar to show ip cache > show
interfaces
