Port Security

Port Security
 

Port Security with Dynamically Learned and Static MAC Addresses

You can use port security with dynamically learned and static MAC addresses to restrict a port's ingress traffic by limiting the MAC addresses that are allowed to send traffic into the port. When you assign secure MAC addresses to a secure port, the port does not forward ingress traffic that has source addresses outside the group of defined addresses. If you limit the number of secure MAC addresses to one and assign a single secure MAC address, the device attached to that port has the full bandwidth of the port.

A security violation occurs in either of these situations:

•When the maximum number of secure MAC addresses is reached on a secure port and the source MAC address of the ingress traffic is different from any of the identified secure MAC addresses, port security applies the configured violation mode.

•If traffic with a secure MAC address that is configured or learned on one secure port attempts to access another secure port in the same VLAN, applies the configured violation mode.

After you have set the maximum number of secure MAC addresses on a port, port security includes the secure addresses in the address table in one of these ways:

•You can statically configure all secure MAC addresses by using the switchport port-security mac-address mac_address interface configuration command.

•You can allow the port to dynamically configure secure MAC addresses with the MAC addresses of connected devices.

•You can statically configure a number of addresses and allow the rest to be dynamically configured.

If the port has a link-down condition, all dynamically learned addresses are removed.

Following bootup, a reload, or a link-down condition, port security does not populate the address table with dynamically learned MAC addresses until the port receives ingress traffic.

A security violation occurs if the maximum number of secure MAC addresses have been added to the address table and the port receives traffic from a MAC address that is not in the address table.

Port Security with Sticky MAC Addresses

Port security with sticky MAC addresses provides many of the same benefits as port security with static MAC addresses, but sticky MAC addresses can be learned dynamically. Port security with sticky MAC addresses retains dynamically learned MAC addresses during a link-down condition.

If you enter a write memory or copy running-config startup-config command, then port security with sticky MAC addresses saves dynamically learned MAC addresses in the startup-config file and the port does not have to learn addresses from ingress traffic after bootup or a restart.

Port Security with IP Phones

Figure shows an application in which a device connects to the switch through the data port of an IP phone.

Figure Device Connected Through IP Phone

 

 

Because the device is not directly connected to the switch, the switch cannot physically detect a loss of port link if the device is disconnected. Later Cisco IP phones send a Cisco Discovery Protocol (CDP) host presence type length value (TLV) to notify the switch of changes in the attached device's port link state. With Cisco IOS Release 12.2(33)SXI and later releases, the switch recognizes the host presence TLV. Upon receiving a host presence TLV notification of a link down on the IP phone's data port, port security removes from the address table all static, sticky, and dynamically learned MAC addresses. The removed addresses are added again only when the addresses are learned dynamically or configured.

Default Port Security Configuration

Table shows the default port security configuration for an interface.

Table 62-1 Default Port Security Configuration

 
Feature
Default Setting

Port security

Disabled.

Maximum number of secure MAC addresses

1.

Violation mode

Shutdown. The port shuts down when the maximum number of secure MAC addresses is exceeded, and an SNMP trap notification is sent.

Port Security Guidelines and Restrictions

When configuring port security, follow these guidelines:

•With the default port security configuration, to bring all secure ports out of the error-disabled state, enter the errdisable recovery cause psecure-violation global configuration command, or manually reenable the port by entering the shutdown and no shut down interface configuration commands.

•Enter the clear port-security dynamic global configuration command to clear all dynamically learned secure addresses. See the Cisco IOS Master Command List, Release 12.2SX for complete syntax information.

•Port security learns unauthorized MAC addresses with a bit set that causes traffic to them or from them to be dropped. The show mac-address-table command displays the unauthorized MAC addresses, but does not display the state of the bit. (CSCeb76844)

•To preserve dynamically learned sticky MAC addresses and configure them on a port following a bootup or a reload and after the dynamically learned sticky MAC addresses have been learned, you must enter a write memory or copy running-config startup-config command to save them in the startup-config file.

•Port security supports private VLAN (PVLAN) ports.

•Port security supports IEEE 802.1Q tunnel ports.

•Port security does not support Switch Port Analyzer (SPAN) destination ports.

•Port security does not support EtherChannel port-channel interfaces.

•With Cisco IOS Release 12.2(33)SXH and later releases, you can configure port security and 802.1X port-based authentication on the same port. With releases earlier than Cisco IOS Release 12.2(33)SXH:

–If you try to enable 802.1X port-based authentication on a secure port, an error message appears and 802.1X port-based authentication is not enabled on the port.

–If you try to enable port security on a port configured for 802.1X port-based authentication, an error message appears and port security is not enabled on the port.

•Port security supports nonnegotiating trunks.

–Port security only supports trunks configured with these commands:

switchport
switchport trunk encapsulation
switchport mode trunk
switchport nonegotiate

–If you reconfigure a secure access port as a trunk, port security converts all the sticky and static secure addresses on that port that were dynamically learned in the access VLAN to sticky or static secure addresses on the native VLAN of the trunk. Port security removes all secure addresses on the voice VLAN of the access port.

–If you reconfigure a secure trunk as an access port, port security converts all sticky and static addresses learned on the native VLAN to addresses learned on the access VLAN of the access port. Port security removes all addresses learned on VLANs other than the native VLAN.

 

Note Port security uses the VLAN ID configured with the switchport trunk native vlan command for both IEEE 802.1Q trunks and ISL trunks.

•Take care when you enable port security on the ports connected to the adjacent switches when there are redundant links running between the switches because port security might error-disable the ports due to port security violations.
 

Enabling Port Security on a Trunk

Port security supports nonnegotiating trunks.

Caution Because the default number of secure addresses is one and the default violation action is to shut down the port, configure the maximum number of secure MAC addresses on the port before you enable port security on a trunk

To enable port security on a trunk, perform this task:

 
 
Command
Purpose

Step 1 

Router(config)# interface type1  slot/port

Selects the LAN port to configure.

Step 2 

Router(config-if)# switchport

Configures the port as a Layer 2 port.

Step 3 

Router(config-if)# switchport trunk encapsulation {isl | dot1q}

Configures the encapsulation, which configures the Layer 2 switching port as either an ISL or 802.1Q trunk.

Step 4 

Router(config-if)# switchport mode trunk

Configures the port to trunk unconditionally.

Step 5 

Router(config-if)# switchport nonegotiate

Configures the trunk not to use DTP.

Step 6 

Router(config-if)# switchport port-security

Enables port security on the trunk.

Step 7 

Router(config-if)# do show port-security interface type1 slot/port | include Port Security

Verifies the configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

 

This example shows how to configure Fast Ethernet port 5/36 as a nonnegotiating trunk and enable port security: 

Router# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# interface fastethernet 5/36 

Router(config-if)# switchport 

Router(config-if)# switchport mode trunk 

Router(config-if)# switchport nonegotiate 

Router(config-if)# switchport port-security 

Router(config-if)# do show port-security interface fastethernet 5/36 | include Port 
Security 

Port Security              : Enabled

Enabling Port Security on an Access Port

To enable port security on an access port, perform this task:

 
 
Command
Purpose

Step 1 

Router(config)# interface type1  slot/port

Selects the LAN port to configure.

Note The port can be a tunnel port or a PVLAN port.

Step 2 

Router(config-if)# switchport

Configures the port as a Layer 2 port.

Step 3 

Router(config-if)# switchport mode access

Configures the port as a Layer 2 access port.

Note A port in the default mode (dynamic desirable) cannot be configured as a secure port.

Step 4 

Router(config-if)# switchport port-security

Enables port security on the port.

Step 5 

Router(config-if)# do show port-security interface type1 slot/port | include Port Security

Verifies the configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

 

This example shows how to enable port security on Fast Ethernet port 5/12: 

Router# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# interface fastethernet 5/12

Router(config-if)# switchport 

Router(config-if)# switchport mode access

Router(config-if)# switchport port-security

Router(config-if)# do show port-security interface fastethernet 5/12 | include Port 
Security

Port Security              : Enabled

Configuring the Maximum Number of Secure MAC Addresses on a Port

To configure the maximum number of secure MAC addresses on a port, perform this task:

 

 
 
Command
Purpose

Step 1 

Router(config)# interface type1  slot/port

Selects the LAN port to configure.

Step 2 

Router(config-if)# switchport port-security maximum number_of_addresses vlan {vlan_ID | vlan_range}

Sets the maximum number of secure MAC addresses for the port (default is 1).

Note Per-VLAN configuration is supported only on trunks.

Step 3 

Router(config-if)# do show port-security interface type1 slot/port | include Maximum

Verifies the configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

When configuring the maximum number of secure MAC addresses on a port, note the following information:

•The range for number_of_addresses is 1 to 4,097.

•Port security supports trunks.

–On a trunk, you can configure the maximum number of secure MAC addresses both on the trunk and for all the VLANs on the trunk.

–You can configure the maximum number of secure MAC addresses on a single VLAN or a range of VLANs.

–For a range of VLANs, enter a dash-separated pair of VLAN numbers.

–You can enter a comma-separated list of VLAN numbers and dash-separated pairs of VLAN numbers.

This example shows how to configure a maximum of 64 secure MAC addresses on Fast Ethernet port 5/12: 

Router# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# interface fastethernet 3/12

Router(config-if)# switchport port-security maximum 64 

Router(config-if)# do show port-security interface fastethernet 5/12 | include Maximum

Maximum MAC Addresses      : 64

Enabling Port Security with Sticky MAC Addresses on a Port

To enable port security with sticky MAC addresses on a port, perform this task:

 
 
Command
Purpose

Step 1 

Router(config)# interface type1  slot/port

Selects the LAN port to configure.

Step 2 

Router(config-if)# switchport port-security mac-address sticky

Enables port security with sticky MAC addresses on a port.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

When enabling port security with sticky MAC addresses, note the following information:

•When you enter the switchport port-security mac-address sticky command:

–All dynamically learned secure MAC addresses on the port are converted to sticky secure MAC addresses.

–Static secure MAC addresses are not converted to sticky MAC addresses.

–Secure MAC addresses dynamically learned in a voice VLAN are not converted to sticky MAC addresses.

–New dynamically learned secure MAC addresses are sticky.

•When you enter the no switchport port-security mac-address sticky command, all sticky secure MAC addresses on the port are converted to dynamic secure MAC addresses.

•To preserve dynamically learned sticky MAC addresses and configure them on a port following a bootup or a reload, after the dynamically learned sticky MAC addresses have been learned, you must enter a write memory or copy running-config startup-config command to save them in the startup-config file.

This example shows how to enable port security with sticky MAC addresses on Fast Ethernet port 5/12: 

Router# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# interface fastethernet 5/12 

Router(config-if)# switchport port-security mac-address sticky

Displaying Port Security Settings

To display port security settings, enter this command:

 
Command
Purpose

Router# show port-security [interface {{vlan vlan_ID} | {type1  slot/port}}] [address]

Displays port security settings for the switch or for the specified interface.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

When displaying port security settings, note the following information:

•Port security supports the vlan keyword only on trunks.

•Enter the address keyword to display secure MAC addresses, with aging information for each address, globally for the switch or per interface.

•The display includes these values:

–The maximum allowed number of secure MAC addresses for each interface

–The number of secure MAC addresses on the interface

–The number of security violations that have occurred

–The violation mode.

This example displays output from the show port-security command when you do not enter an interface: 

Router# show port-security

Secure Port      MaxSecureAddr  CurrentAddr  SecurityViolation  Security

Action

                    (Count)        (Count)      (Count)

----------------------------------------------------------------------------
 
     Fa5/1           11            11            0            Shutdown

     Fa5/5           15            5             0            Restrict

     Fa5/11          5             4             0            Protect

----------------------------------------------------------------------------
 
Total Addresses in System: 21

Max Addresses limit in System: 128

This example displays output from the show port-security command for a specified interface: 

Router# show port-security interface fastethernet 5/1

Port Security: Enabled

Port status: SecureUp

Violation mode: Shutdown

Maximum MAC Addresses: 11

Total MAC Addresses: 11

Configured MAC Addresses: 3

Aging time: 20 mins

Aging type: Inactivity

SecureStatic address aging: Enabled

Security Violation count: 0

This example displays the output from the show port-security address privileged EXEC command: 

Router# show port-security address

          Secure Mac Address Table

-------------------------------------------------------------------

Vlan    Mac Address       Type                Ports   Remaining Age

                                                         (mins)

----    -----------       ----                -----   -------------

   1    0001.0001.0001    SecureDynamic       Fa5/1      15 (I)

   1    0001.0001.0002    SecureDynamic       Fa5/1      15 (I)

   1    0001.0001.1111    SecureConfigured    Fa5/1      16 (I)

   1    0001.0001.1112    SecureConfigured    Fa5/1      -

   1    0001.0001.1113    SecureConfigured    Fa5/1      -

   1    0005.0005.0001    SecureConfigured    Fa5/5      23

   1    0005.0005.0002    SecureConfigured    Fa5/5      23

   1    0005.0005.0003    SecureConfigured    Fa5/5      23

   1    0011.0011.0001    SecureConfigured    Fa5/11     25 (I)

   1    0011.0011.0002    SecureConfigured    Fa5/11     25 (I)

-------------------------------------------------------------------

Total Addresses in System: 10

Max Addresses limit in System: 128


	

	




 



    




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