The Basics of Layer 2 Network Mapping

Layer 2 network mapping gives IT and network professionals valuable information about how devices are physically connected. What is Layer 2, and what can you do with it? 

What is Layer 2?

Layer 2 refers to the data link layer of the network. This is how data moves across the physical links in your network. It's how switches within your network talk to one another. Installing Layer 2 on your infrastructure gives you high-speed connectivity between devices. It can also provide you with improved network performance.

To create a Layer 2 map of your network, network mapping software will look at your devices and the data they provide. Specifically, it will look at the SNMP-Bridge MIB to tell you how your network is constructed based on what it sees.

Nowadays, software that can create Layer 2 outputs or maps is a necessity for many IT professionals because of the details it can give you.

What is the Difference Between Layer 2 and Layer 3?

While Layer 2 is the data link layer of your network, Layer 3 uses IP addresses to communicate between network infrastructure. Layer 3 mapping scans for IPs of devices and determines the networks and subnets they're associated with to build out the Layer 3 map.

Layer 2 Network Mapping 

When you enable Layer 2, you're able to see much more information on the state of your network. Here's what you can do with Layer 2:

• See what's connected to your switches
• Discover a device's MAC address and what VLAN it's connected to
• Eliminate the need for cable tracing by easily seeing what a port is connected to
• Identify spare ports on your network
• Discover problem machines on your network and shut down the port
• Search your network by MAC address to find a missing machine
• Avoid network shutdowns by identifying switch loopbacks
• Identify switch-to-switch connections and build a backbone Layer 2 map
• Build Layer 2 network maps one switch at a time or of the whole network using auto-discovery

Layer 2 Protocols

There are several Layer 2 protocols used during the engine scan. These include: 

• SNMP: Simple Network Management Protocol is used for collecting information from devices and configuring them.
• CDP: Cisco Discovery Protocol is used to share information about directly-connected Cisco equipment
• LLDP: Link Layer Discovery Protocol is used to advertise the identity, capabilities, and neighbors on a wired LAN Ethernet. It gathers the sys name, description, port name, VLAN, etc.
• STP: Spanning Tree Protocol works on the switch of a bridged Ethernet LAN, ensuring you do not create loops when you have a redundant path in your network.
• ARP: Address Resolution Protocol is used to map an IP address to a physical address (MAC) that is recognized on the local device.
• FDB: Forwarding Database is used by Layer 2 devices to store which ports the mac was learned on. When an Ethernet frame arrives at a Layer 2 device, the Layer 2 device will inspect the destination MAC address of the frame and look to its FDB table for information on where to send that specific Ethernet frame.

Optimizing Your Network for Layer 2

Your Layer 2 data will only be as good as your network configuration. If your devices aren’t configured properly, the Layer 2 information you receive won’t be very accurate.

They are still many networks out there that are running older SNMP implementations or don’t even have SNMP turned on. This will directly impact their ability to discover and map Layer 2 connections. So if you want Layer 2 data, it’s important to first and foremost optimize your network by making sure your infrastructure has been configured properly.

When you use Layer 2 with a network mapping software, any map containing Layer 2 switches can be updated automatically to show how those devices are interconnected and the ports through which they are connected. These tools typically provide you with multiple Layer 2 scanning options. You can either do a full scan of your entire infrastructure to include endpoint connects, or throttle the scan to just display your switching backbone.

Layer 2 gives you a detailed account of network activity and device statuses. You'll be able to easily find out how devices were configured and if they're performing up to par in real time. Finding a reliable network monitoring solution that allows you to create Layer 2 maps will help you keep your network running smoothly.