Switch restricts MAC address access

Switches can restrict network access by allowing or blocking devices based on their MAC addresses using MAC filtering or port security.How MAC Filtering WorksMAC filtering is a network access control method where a switch or router checks a device's MAC (Media Access Control) address against a configured list to determine whether it can connect to the network . There are two main modes:Allow list (whitelist): Only devices with MAC addresses explicitly listed are permitted to access the network.Deny list (blacklist): Devices with MAC addresses on the list are blocked, while all others are allowed . MAC filtering can be enforced at the connection layer, preventing the device from joining the network, or at the DHCP layer, allowing connection but denying an IP address so network services cannot be used .Port Security on SwitchesOn managed switches, especially Cisco devices, port security is commonly used to restrict MAC addresses per port . Key features include:Static MAC addresses: Only specific MAC addresses are allowed on a port.Sticky MAC addresses: The switch dynamically learns MAC addresses and adds them to the allowed list.Violation actions: When an unauthorized MAC address is detected, the switch can protect (ignore traffic), restrict (log and drop traffic), or shutdown the port . Example Cisco commands for port security:CodeCopyswitchport mode accessswitchport port-securityswitchport port-security mac-address switchport port-security violation restrict This setup ensures that unknown devices are blocked immediately when they attempt to connect .MAC Access Control Lists (ACLs)MAC ACLs can also be applied to restrict non-IP traffic at Layer 2, but they are less flexible than port security for general device access control . They are mainly used in bridging scenarios rather than for general network access restriction.Considerations and LimitationsSecurity: MAC addresses can be spoofed, so MAC filtering or port security should be combined with stronger authentication methods like 802.1X or RADIUS for robust security .Scalability: Maintaining large allow or deny lists manually can be cumbersome, especially in networks with many devices .Network management: Changes in device inventory require updating MAC lists to avoid accidental lockouts . In summary, switches can restrict access by using MAC filtering, port security, or MAC ACLs, with port security being the most practical for per-port control. For enterprise networks, combining these methods with authentication servers provides stronger protection against unauthorized devices.