It is generally detectable when you begin to suffer latency and slowness within the network, however the most common failure within this type of infrastructure is when one of the client-side equipment injects dhcp into the infrastructure, this causes the broadcast to extend. through the network leads to a total downtime, so it is important to segment and route within the network so that this problem does not occur. 

Determining failures at Layer 2 (Data Link) of a network can be a detailed process that involves diagnosing problems related to the physical connection, detecting collisions, excessive broadcast traffic problems, and VLAN configuration errors. , among others.

Here are some common strategies and tools that can be used to identify and diagnose Layer 2 failures:

1. Review of Physical Indicators

• Status Lights on Devices: Check the status lights on switches, routers, and NICs (Network Interface Cards) to see if they indicate any physical problems, such as disconnections or hardware problems.
• Cable Verification: Make sure all cables are connected correctly and are not damaged. A faulty cable can cause connectivity issues and packet loss.

2. software tools

• Diagnostic Commands: Use commands like ping, traceroute, and operating system-specific tools to diagnose connectivity and traffic routing. Although these tools operate at higher layers, they can help identify if the problem originates at Layer 2.
• Network Monitors and Protocol Analyzers: Tools like Wireshark can capture and analyze network traffic, identifying problems such as excessive collisions, frame errors, and unusually high broadcast traffic.

3. Review of Configurations and Logs

• System and Device Logs: Review event logs on your network devices. Switches and routers often log warnings and errors that may indicate problems at Layer 2.
• VLAN configuration: Verify that VLANs are configured correctly on all relevant devices and that ports are assigned to the correct VLANs.

4. Performance Analysis

• Bandwidth Usage and Traffic Analysis: Network monitoring tools can help identify performance bottlenecks and unusual traffic patterns that could indicate problems at Layer 2.

5. Layer 2 Specific Tests

• Ethernet Loopback Tests: Some devices allow configuration of loopback tests to verify port operation and Layer 2 communication.
• Checking the MAC Table: Checking MAC tables on switches can help identify address learning issues or ports incorrectly blocked by the Spanning Tree Protocol (STP).

6. Identification of Common Errors

• Duplex and Speed ​​Errors: Make sure connected devices agree to the correct speed and duplex settings to avoid performance issues.

When addressing problems at Layer 2, it is crucial to proceed systematically, ruling out other possible causes of network problems and using a combination of hardware and software tools to diagnose and fix identified problems.