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6.3. Port Security
The Switch will learn the MAC address of the device directly connected to a particular port and
allow traffic through. We will ask the question: “How do we control who and how many can
connect to a switch port?” This is where port security can assist us. The Switch allow us to
control which devices can connect to a switch port or how many of them can connect to it (such
as when a hub or another switch is connected to the port).
Let’s say we have only one switch port left free and we need to connect five hosts to it. What
can we do? Connect a hub or switch to the free port! Connecting a switch or a hub to a port has
implications. It means that the network will have more traffic. If a switch or a hub is connected
by a user instead of an administrator, then there are chances that loops will be created. So, it is
best that number of hosts allowed to connect is restricted at the switch level. This can be done
using the “port-security limit” command. This command configures the maximum number of
MAC addresses that can source traffic through a port.
Port security can sets maximum number of MAC addresses allowed per interface. When the
limit is exceeded, incoming packets with new MAC addresses are dropped. It can be use MAC
table to check it. The static MAC addresses are included for the limit.
Note : If you configure a port of the Switch from disabled to enabled, all of the MAC learned by
this port will be clear.
Default Settings:
The port security on the Switch is disabled.
The Maximum MAC per port is 5.
The port state of the port security is disabled.
6.3.1. CLI Configuration
Node Command Description
enable show port-security This command displays the current port security
configurations.
enable configure terminal This command changes the node to configure node.
configure port-security
(disable|enable)
This command enables / disables the global port security
function.
configure interface IFNAME This command enters the interface configure node.
interface port-security
(disable|enable)
This command enables / disables the port security
function on the specific port.
interface port-security limit
<1-1000>
This command configures the maximum MAC entries
on the specific port.
configure interface range
gigabitethernet1/0/
PORTLISTS
This command enters the if-range configure node.
if-range port-security
(disable|enable)
This command enables / disables the port security
function for the specified ports
if-range port-security limit
<1-1000>
This command configures the maximum MAC entries
for the specified ports.