44
NETWORKS
Port Security
This page allows you to configure the Port Security global and per-port settings. Port Security allows for limiting the
number of users on a given port. A user is identified by a MAC address and VLAN ID. If Port Security is enabled on a
port, the limit specifies the maximum number of users on the port. If this number is exceeded, an action is taken
depending on violation mode. The violation mode can be one of the four different described below.
The Port Security configuration consists of two sections, a global and a per-port.
Global Configuration
Aging Enabled
If checked, secured MAC addresses are subject to aging as discussed under Aging Period.
Aging Period
If Aging Enabled is checked, then the aging period is controlled with this input. If other modules are using
the underlying functionality for securing MAC addresses, they may have other requirements to the aging
period. The underlying functionality will use the shorter requested aging period of all modules that have
aging enabled.
The Aging Period can be set to a number between 10 and 10000000 seconds with a default of 3600 seconds.
To understand why aging may be desired, consider the following scenario: Suppose an end-host is connected
to a 3rd party switch or hub, which in turn is connected to a port on this switch on which Port Security is
enabled. The end-host will be allowed to forward if the limit is not exceeded. Now suppose that the end-host
logs off or powers down. If it wasn't for aging, the end-host would still take up resources on this switch and
will be allowed to forward. To overcome this situation, enable aging. With aging enabled, a timer is started
once the end-host gets secured. When the timer expires, the switch starts looking for frames from the
end-host, and if such frames are not seen within the next Aging Period, the end-host is assumed to be
disconnected, and the corresponding resources are freed on the switch.
Hold Time
The hold time - measured in seconds - is used to determine how long a MAC address is held in the MAC table
if it has been found to violate the limit. Valid range is between 10 and 10000000 seconds with a default
of 300 seconds. The reason for holding a violating MAC address in the MAC table is primarily to ensure that
the same MAC address doesn't give rise to continuous notifications (if notifications on violation count is
