Understanding Port Security

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You use port security to ensure only authorized clients can connect to a network. If you’re planning on taking the Security+ exam, you should have a basic understanding of port security and how it can be implemented.

For example, can you answer this question?

Q. Your organization frequently has guests visiting in various conference rooms throughout the building. These guests need access to the Internet via wall jacks, but should not be able to access internal network resources. Employees need access to both the internal network and the Internet. What would BEST meet this need?

A. PAT and NAT

B. DMZ and VPN

C. VLANs and 802.1x

D. Routers and Layer 3 switches

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

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Port Security

Port security limits the computers that can connect to ports on a switch. At the most basic level, administrators disable unused ports. For example, individual RJ-45 wall jacks in an office lead to specific physical ports on a switch. If the wall jack is not being used, administrators can disable the physical port on the switch. This prevents someone from plugging in a laptop or other computer into the wall jack and connecting to the network.

MAC address filtering is another example of port security. In a simple implementation, the switch remembers the first one or two MAC addresses that connect to a port. It then blocks access to systems using any other MAC addresses. You can also manually configure each port to accept traffic only from a specific MAC address. This limits each port’s connectivity to a specific device using this MAC address. This can be very labor intensive, but it provides a higher level of security.

Port Security

802.1x Port Security

The 802.1x protocol is a port-based authentication protocol and it provides much stronger port security than simply disabling unused ports or using MAC address filtering. It requires users or devices to authenticate when they connect to a specific access point, or a specific physical port, and can be implemented in both wireless and wired networks. It secures the authentication process prior to a client gaining access to a network, and blocks network access if the client cannot authenticate.

You can implement 802.1x as a Remote Authentication Dial-In User Service (RADIUS) or Diameter server. RADIUS provides centralized authentication, and Diameter is an improvement over RADIUS, supporting additional features such as Extensible Authentication Protocol (EAP). 802.1x also supports EAP and can be implemented to require authentication using multiple methods, including digital certificates.

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The 802.1x server will prevent rogue devices from connecting to a network. Consider open RJ-45 wall jacks. Although disabling them is a good port security practice, you can also configure an 802.1x server to require authentication for these ports. If clients cannot authenticate, the 802.1x server blocks or restricts access to the network.

It’s possible to combine an 802.1x server with other network elements such as a VLAN. For example, imagine you want to provide visitors with Internet access, but prevent them from accessing internal network resources. You can configure the 802.1x server to grant full access to authorized clients, but redirect unauthorized clients to another area of the network via a VLAN.

VLAN

A virtual local area network (VLAN) uses a switch to group several different computers into a virtual network. You can group the computers together based on departments, job function, or any other administrative need. This provides security because you’re able to isolate the traffic between the computers in the VLAN.

Normally, a router would group different computers onto different subnets, based on physical locations. All the computers in a routed segment are located in the same physical location, such as on a specific floor or wing of a building.

However, a single switch can create multiple VLANs to separate the computers based on logical needs rather than physical location. Additionally, administrators can easily reconfigure the switch to add or subtract computers from any VLAN if the need arises.

For example, a group of users who normally work in separate departments may begin work on a project that requires them to be on the same subnet. You can configure a switch to logically group these workers together, even if the computers are physically located on different floors or different wings of the building. When the project is over, you can simply reconfigure the switch to return the network to its original configuration.

Similarly, you can use a single switch with multiple VLANs to separate users. For example, if you want to separate the traffic between the HR department and the IT department, you can use a single switch with two VLANs. The VLANs logically separate all the computers between the two different departments, even if the computers are located close to each other.

Remember this

You can create multiple VLANs with a single switch. A VLAN can logically group several different computers together, or logically separate computers, without regard to their physical location.


 

Q. Your organization frequently has guests visiting in various conference rooms throughout the building. These guests need access to the Internet via wall jacks, but should not be able to access internal network resources. Employees need access to both the internal network and the Internet. What would BEST meet this need?

A. PAT and NAT

B. DMZ and VPN

C. VLANs and 802.1x

D. Routers and Layer 3 switches

Answer is C. An 802.1x server provides port-based authentication and can authenticate clients. Clients that cannot authenticate (the guests in this scenario) can be redirected to a virtual local area network (VLAN) that grants them Internet access, but not access to the internal network. None of the other solutions provides port security or adequate network separation.

Port Address Translation (PAT) and Network Address Translation (NAT) each translate private IP addresses to public IP addresses.

A demilitarized zone (DMZ) provides a buffer zone between a public network and a private network for public-facing servers.

A virtual private network (VPN) provides access to a private network via a public network.

Routers work on Layer 3, and Layer 3 switches mimic some of the functionality of routers.

See Chapter 3 of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide for more information on basic network security.

 

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