In a Cisco switch, what is the default period of time after which a MAC address ages out and is discarded?

A.
100 seconds

B.
180 seconds

C.
300 seconds

D.
600 seconds

Explanation:
To configure the aging time for all MAC addresses, perform this task:

Command
Purpose
Step 1
switch# configure terminal
Enters configuration mode.
Step 2
switch(config)# mac-address-table aging-time seconds [vlan vlan_id] Specifies the time before an entry ages out and is discarded from the MAC address table. The
range is from 0 to 1000000; the default is 300 seconds. Entering the value 0 disables the MAC

aging. If a VLAN is not specified, the aging specification applies to all VLANs.

http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/configuration/guide/cli/MAC Address.html