The OSI Model and You Part 2: The Data Link Layer

May 31, 2021
| |
3 min read

If the physical layer we talked about earlier in this series about OSI layers is the ‘what’ that allows data to travel, the data link layer is the ‘how.’ In the previous piece of this seven-part series on the OSI model, we described the physical layer and what cybersecurity threats could impact it. Remember, the key takeaway on how to protect the physical layer is this: business impact, contingency planning and continuity. NIST Special Publication 800-34 Revision 1, Contingency Planning Guide for Federal Information Systems, is one of your best friends here. Now, let’s take a look at the data link layer.

What Is the Data Link Layer in OSI Layers?

In this part of the OSI seven-layer framework, zeroes and ones can travel between physically connected points. To get technical for a moment: nodes. And for clarification here, a wireless connection — such as a computer to a router over Wi-Fi — counts as a physical connection for the purposes of the OSI layers model.

This part of the OSI data link layer governs how much data should be allowed to travel and how long it should take to travel over a certain distance. In addition, very importantly, it keeps an eye out for errors in data transmission. The data link layer is also made up of two sublayers: the Media Access Control (MAC) sublayer — the unique identifier of a device — and the Logical Link Control (LLC) sublayer — the interface between the device and the network layer, which comes next in the OSI model. Many of the specifications for this part of the OSI layers can be found in the Institute of Electrical and Electronics Engineers IEEE 802 Standard for Local and Metropolitan Area Networks. (If you ever wondered why the number 802.11 is in front of many Wi-Fi devices, now you know: it represents the device is compliant with IEEE 802, subpart 11.)

Cybersecurity Threats to the Data Link in OSI Layers

The data link layer is where malicious actors can begin to take advantage of the frame, a piece of information that is part of the transmission on this part of the OSI layers. Each frame has a header, body and trailer. If attackers can view or manipulate these frames, then they can compromise your data. This layer can also suffer from overload, degrading performance. The types of attacks you need to be concerned about here are MAC address spoofing, MAC address flooding, virtual local area network (LAN) circumvention and address resolution protocol poisoning.

Reducing Threats to the Seven Layers of Networking

To reduce vulnerability at this section of the OSI layers, have a ‘batten down the hatch’ type mentality, where you should expect a storm. And the best way to prepare for that storm is by limiting control and access wherever possible. There are a few ways to do that.

One of the best ways is encryption. Some protocols may be inherently insecure, so you fill that gap through encryption. If you are unsure of what encryption method is right for you, you cannot go wrong by spending some time reviewing NIST Special Publication 800-175B Revision 1.

Two other simple and effective techniques for securing the data link section of the OSI layers are disabling ports, therefore denying access, and enabling MAC address filtering. If you’re not on the guest list, sorry, you can’t join the party (or network). You also want to prevent virtual LAN (VLAN) hopping, a way an attacker sneaks their way into the party. This is a more sophisticated way to attack the data link layer, but it still can happen. Misconfigurations and poor VLAN implementation are normally the cause of this vulnerability.

Keeping these techniques in mind will help lock down this layer. In the next piece, we will talk about how to secure the next of the OSI layers, the network layer.

George Platsis
Senior Lead Technologist, Educator and Author

George Platsis works with the private, public and nonprofit sectors to address their strategic, operational and training needs, focusing on projects related ...
read more