To build a secure layer 2 switch network that avoids loops involves several key steps.

Here is a detailed step-by-step guide to help you build a secure layer 2 switch network that avoids loops using STP, BPDU, MAC filtering, and removing the native VLAN:

Step 1: Plan and design your network

Before you begin building your network, you should first plan and design it. Determine the number of switches you will need and how they will be interconnected. Consider the network topology, bandwidth requirements, and any security requirements.

Step 2: Choose your switches

Choose your switches based on your network design and requirements. Make sure the switches you select support the required features, such as VLANs, Quality of Service (QoS), and Link Aggregation Control Protocol (LACP). Also, ensure that the switches have the necessary security features, such as Access Control Lists (ACLs), Secure Shell (SSH), and Simple Network Management Protocol (SNMP).

Step 3: Configure basic switch settings

Configure basic switch settings, such as hostname, IP address, and default gateway. Also, enable password protection for the switch to prevent unauthorized access.

Step 4: Configure VLANs

Configure VLANs to segment your network into smaller logical networks. This can help improve network performance and security. Assign each port on the switch to the appropriate VLAN.

Step 5: Configure Spanning Tree Protocol (STP)

Configure STP to prevent loops in the network. STP is a protocol that helps prevent loops by blocking redundant links in the network. Configure STP on all switches in the network.

Step 6: Configure Bridge Protocol Data Unit (BPDU) guard

Configure BPDU guard to prevent rogue switches from being connected to the network. BPDU guard blocks any port that receives a BPDU, which can help prevent loops in the network.

Step 7: Configure MAC filtering

Configure MAC filtering to allow only authorized devices to connect to the network. MAC filtering can help prevent rogue devices from being connected to the network, which can help prevent loops.

Step 8: Remove the native VLAN

Remove the native VLAN to prevent VLAN hopping attacks. VLAN hopping attacks occur when a device on one VLAN gains access to traffic on another VLAN. Removing the native VLAN can help prevent these types of attacks.

Step 9: Verify STP, BPDU guard, MAC filtering, and native VLAN configuration

Verify that the STP, BPDU guard, MAC filtering, and native VLAN configuration is correct and that there are no loops in the network. Use tools such as the show spanning-tree command to view the STP and RSTP topology.

Step 10: Monitor network activity

Monitor network activity to detect and respond to potential security threats. Use tools such as SNMP and syslog to monitor network activity and identify potential issues.