C
HAPTER
25
| General Security Measures
Port Security
– 876 –
COMMAND MODE
Interface Configuration (Ethernet)
COMMAND USAGE
◆ The default maximum number of MAC addresses allowed on a secure
port is zero (that is, port security is disabled). To use port security, you
must configure the maximum number of addresses allowed on a port
using the port security max-mac-count command.
◆ When port security is enabled using the port security command, or
the maximum number or allowed addresses is set to value lower than
the current limit after port security has been enabled, the switch first
clears all dynamically learned entries from the address table. It then
starts learning new MAC addresses on the specified port, and stops
learning addresses when it reaches a configured maximum number.
Only incoming traffic with source addresses already stored in the
dynamic or static address table will be accepted.
◆ To configure the maximum number of address entries which can be
learned on a port, specify the maximum number of dynamic addresses
allowed. The switch will learn up to the maximum number of allowed
address pairs <source MAC address, VLAN> for frames received on the
port. (The specified maximum address count is effective when port
security is enabled or disabled.) Note that you can manually add
additional secure addresses to a port using the mac-address-table
static command. When the port has reached the maximum number of
MAC addresses, the port will stop learning new addresses. The MAC
addresses already in the address table will be retained and will not be
aged out.
◆ MAC addresses that port security has learned, can be saved in the
configuration file as static entries. See command port security
mac-address-as-permanent.
◆ If port security is enabled, and the maximum number of allowed
addresses are set to a non-zero value, any device not in the address
table that attempts to use the port will be prevented from accessing the
switch.
◆ If a port is disabled due to a security violation, it must be manually re-
enabled using the no shutdown command.
◆ A secure port has the following restrictions:
■
Cannot be connected to a network interconnection device.
■
Cannot be a trunk port.
EXAMPLE
The following example enables port security for port 5, and sets the
response to a security violation to issue a trap message:
Console(config)#interface ethernet 1/5
Console(config-if)#port security action trap
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