Switchport Security Configuration

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Overview

The switchport security feature (Port Security) is an important piece of the network switch security puzzle; it provides the ability to limit what addresses will be allowed to send traffic on individual switchports within the switched network.

Once an organization decides to utilize the switchport security feature on their networks, it is important to carefully plan before any configuration is put in place. While the switchport security feature is very useful if used correctly, it can easily be misconfigured; this misconfiguration can cause service interruption and ongoing headaches for an organization. The planning of the configuration includes determining which violation mode and operation mode to use based on the goals of the organization, as well as determining which switchports should be enabled with the feature. This article takes a look at how the switchport security feature is configured by extending on the concepts that were covered in Switchport Security Concepts.

 

Switchport Security Configuration

By default, the switchport security feature is disabled on all switchports and must be enabled. Table 1 shows the steps required to enable the switchport security feature on an interface (This can cause some confusion, but when using Cisco IOS, switchport configuration is performed while in interface configuration mode. The terms interface and switchport are interchangeable).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Enter privileged mode router>enable
Enter global configuration mode router#configure terminal
Enter interface configuration mode router(config)#interface interface
Enable the switchport security feature router(config-if)#switchport port-security

Without configuring any other specific parameters, the switchport security feature will only permit one MAC address to be learned per switchport (dynamically) and use the shutdown violation mode; this means that if a second MAC address is seen on the switchport the port will be shutdown and put into the err-disabled state.

Table 2 shows the steps required to alter these default parameters:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Enter privileged mode router>enable
Enter global configuration mode router#configure terminal
Enter interface configuration mode router(config)#interface interface
Configure the maximum number of MAC addresses allowed on a switchport (default : 1) router(config-if)#switchport port-security maximum value
Configure the switchport violation mode (default : shutdown) router(config-if)#switchport port-security violation {protect | restrict | shutdown}

As stated above, by default MAC addresses are learned on a switchport dynamically and are called dynamic MAC addresses. MAC addresses can also be configured in two other ways: statically and sticky. Static MAC addresses can be configured on a switchport to ensure that only a device with a specific MAC can utilize a switchport (for example, if the switchport location and a device are publically accessible and the organization wants to ensure only that authorized device can access the network). A sticky MAC address is a hybrid between a static and dynamic MAC address.  When it is dynamically learned, the MAC address is automatically entered into the running configuration as a static MAC address; the address is then kept in the running configuration until a reboot. On reboot, the MAC address will be lost; if the network engineer wants to keep the MAC address across a reboot a configuration save is required (copy running startup).

Table 3 shows the steps required to configure a static MAC address:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Enter global configuration mode router#configure terminal
Enter interface configuration mode router(config)#interface interface
Configure a static MAC address router(config-if)#switchport port-security mac-address mac-address

Table 4 shows the steps required to enable the use of sticky learning on a switchport:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Enter global configuration mode router#configure terminal
Enter interface configuration mode router(config)#interface interface
Enabling the use of sticky MAC address learning router(config-if)#switchport port-security mac-address sticky

 

Switchport Security Configuration Example

To wrap the configuration commands into a single example to ensure clarity, this section will show a basic switchport security example.

The configuration shown in Table 5 will enable the use of the switchport security feature on ports f0/1 and f0/2, statically configure the 0000.1111.2222 MAC address on the f0/1 switchport and enable sticky learning on the f0/2 switchport.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Enter global configuration mode router#configure terminal
Enter interface configuration mode router(config)#interface f0/1
Enabling the switchport security feature router(config-if)#switchport port-security
Configuring a static MAC Address (0000.1111.2222) on the switchport. router(config-if)#switchport port-security mac-address 0000.1111.2222
Enter interface configuration mode router(config)#interface f0/2
Enabling the switchport security feature router(config-if)#switchport port-security
Configuring the use of sticky MAC address learning router(config-if)#switchport port-security mac-address sticky

 

Summary

While the switchport security feature does not require that many commands to operate properly, it can also be misconfigured just as easily. Take the time to write down and triple-check that the proposed configuration is doing what is expected, and/or test a proposed configuration in a non production environment. Hopefully the content in this article can be used to get started with the switchport security feature.

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Contributor

Sean Wilkins

Sean Wilkins is an accomplished networking consultant who has been in the IT field for more than 20 years, working with several large enterprises. He is a writer for infoDispersion and his educational accomplishments include: a Master’s of Science in Information Technology with a focus in Network Architecture and Design, and a Master’s of Science in Organizational Management. Sean holds certifications with Cisco (CCNP/CCDP), Microsoft (MCSE) and CompTIA (A+ and Network+).