Final answer:
A single network port may show two MAC addresses if it's part of a managed switch or if there are virtual machines or interfaces using the same physical connection.
Step-by-step explanation:
One port may show two MAC addresses due to the presence of a managed switch or networking device that uses multiple MAC addresses for its operations. Network switches often have a MAC address for each port as well as a MAC address for the whole device itself, which can be seen by attached devices. This situation occurs because switches operate at the data link layer (Layer 2) of the OSI model and require MAC addresses to manage traffic between devices. This can also happen in virtual environments where virtual machines (VMs) or virtual interfaces are assigned unique MAC addresses while sharing a single physical network port. Additionally, port security features may learn and limit the number of MAC addresses allowed on a port for security purposes.
One port can have two MAC addresses because of VLAN (Virtual Local Area Network) tagging. VLAN tagging allows multiple VLANs to share the same physical network infrastructure. Each VLAN has its own MAC address table, and the switch can switch frames between different VLANs based on these MAC addresses. Hence, a single port can have multiple MAC addresses. This is part of network management to control traffic or for security features.
For example, consider a scenario where a switch has two VLANs connected to a single port. Each VLAN has its MAC address table. If a device in one VLAN sends a frame to a device in the other VLAN, the switch will use MAC addresses from the respective VLAN's table to forward the frame.
In addition to VLAN tagging, a port may have two MAC addresses if it is using MAC address spoofing. MAC address spoofing is a technique in which a device changes its MAC address to impersonate another device or to evade network security measures