The base show interfaces command outputs quite a bit of information. In addition to the basic up or down status information, the show interfaces command includes these tasty informational nuggets:

  • CoS queues: This is the total number of CoS queues configured for the particular interface card. If you’ve configured eight queues, it shows a value of eight. For this particular interface, only the default four queues are available.

  • Current address and Hardware address: The Current address is the configured MAC address for the interface card. The Hardware address is the actual MAC address tied to the hardware.

  • Last flapped: The Last Flapped field indicates the last time the interface went down and came back up. This information can be very helpful when you’re trying to figure out why traffic is lost on your network. You can correlate the last flapped date and time with changes in your network (maintenance calls, configuration changes, and so on), which can help you track down the source of the issue.

  • Input rate and Output rate: The input and output rates identify the total input and output in packets per second. In this case, the interface is down, so the values are 0.

  • Active alarms and Active defects: The active alarms and defects list the link alarms that are associated with the particular interface. In this case, the link is down, which has generated a LINK alarm. That alarm is listed as both an alarm and a defect.

You can use the base show interfaces command in operational mode:

user@router> show interfaces
Physical interface: fe-0/0/0, Enabled, Physical link is Down
 Interface index: 128, SNMP ifIndex: 23
 Link-level type: Ethernet, MTU: 1514, Speed: 10m, Loopback: Disabled,
 Source filtering: Disabled, Flow control: Enabled
 Device flags  : Present Running Down
 Interface flags: Hardware-Down SNMP-Traps Internal: 0x4000
 Link flags   : None
 CoS queues   : 4 supported, 4 maximum usable queues
 Current address: 00:05:85:02:a4:00, Hardware address: 00:05:85:02:a4:00
 Last flapped  : 2008-03-05 14:30:58 PST (4w3d 23:00 ago)
 Input rate   : 0 bps (0 pps)
 Output rate  : 0 bps (0 pps)
 Active alarms : LINK
 Active defects : LINK