Limit Control

This page allows you to configure the Port Security Limit Control system and port settings.

Limit Control allows for limiting the number of users on a given port. A user is identified by a MAC address and VLAN (Virtual LAN) ID. If Limit Control 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. The action can be one of the four different actions as described below.
The Limit Control module utilizes a lower-layer module, Port Security module, which manages MAC addresses learnt on the port.

The Limit Control configuration consists of two sections: system-wide and port-wide.

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Object Description
System Configuration
Mode Indicates if Limit Control is globally enabled or disabled on the switch. If globally disabled, other modules may still use the underlying functionality, but limit checks and corresponding actions are disabled.
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 port security for securing MAC addresses, they may have other requirements to the aging period. The underlying port security will use the shorter requested aging period of all modules that use the functionality.
The Aging Period can be set to a number between 10 and 10,000,000 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 Limit Control 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.
Port Configuration
Port The port number to which the configuration below applies.
Mode Controls whether Limit Control is enabled on this port. Both this and the Global Mode must be set to Enabled for Limit Control to be in effect. Notice that other modules may still use the underlying port security features without enabling Limit Control on a given port.
Limit The maximum number of MAC addresses that can be secured on this port. This number cannot exceed 1024. If the limit is exceeded, the corresponding action is taken.
The switch is “born” with a total number of MAC addresses from which all ports draw whenever a new MAC address is seen on a Port Security-enabled port. Since all ports draw from the same pool, it may happen that a configured maximum cannot be granted, if the remaining ports have already used all available MAC addresses.
Action If Limit is reached, the switch can take one of the following actions:
None: Do not allow more than Limit MAC addresses on the port, but take no further action.
  • Trap: If Limit + 1 MAC addresses is seen on the port, send an SNMP (Simple Network Management Protocol) trap. If Aging is disabled, only one SNMP trap will be sent, but with Aging enabled, new SNMP traps will be sent every time the limit gets exceeded.
  • Shutdown: If Limit + 1 MAC addresses is seen on the port, shut down the port. This implies that all secured MAC addresses will be removed from the port, and no new address will be learned. Even if the link is physically disconnected and reconnected on the port (by disconnecting the cable), the port will remain shut down. There are three ways to re-open the port:
    1. Boot the stack or elect a new master the switch,
    2. Disable and re-enable Limit Control on the port or the stack/switch.
    3. Click the Reopen button.
  • Trap & Shutdown: If Limit + 1 MAC addresses is seen on the port, both the “Trap” and the “Shutdown” actions described above will be taken.
State This column shows the current state of the port as seen from the Limit Control's point of view. The state takes one of four values:
Disabled: Limit Control is either globally disabled or disabled on the port.
  • Ready: The limit is not yet reached. This can be shown for all actions.
  • Limit Reached: Indicates that the limit is reached on this port. This state can only be shown if Action is set to None or Trap.
  • Shutdown: Indicates that the port is shut down by the Limit Control module. This state can only be shown if Action is set to Shutdown or Trap & Shutdown.
Re-open Button If a port is shut down by this module, you may reopen it by clicking this button, which will only be enabled if this is the case. For other methods, refer to Shutdown in the Action section.

Note that clicking the Re-open button causes the page to be refreshed, so non-committed changes will be lost.

../_Common/../Graphics/refresh.png Refresh the page immediately. Any non-committed changes will be lost.
../_Common/../Graphics/save_new.png Save changes.
../_Common/../Graphics/reset_new.png Undo any changes and revert to previously saved values.