Member Avatar for Sivan_1

If all that a switch does is to listen to the packets coming into each port and forms a MAC address table, no host machine sends a packet to only the switch - it only sends to another host. Does this mean that the switch ports do not have any MAC address associated with each of its ports?

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Short answer: no — a normal Layer‑2 switch port is not an end‑station with its own, network‑visible MAC like a PC NIC. A switch learns host MACs from the source field of incoming frames and builds a MAC (CAM) table that maps those host MACs to physical ports. Forwarding uses that table; the MAC on the wire remains the sending host’s NIC MAC and the switch typically does not rewrite it.

That ties together the earlier posts: is right about how the switch learns and maps MACs per port (and why a port connected to another switch will show many MACs). is also correct that Ethernet interfaces have MAC addresses — but those are the switch’s own control/management or logical interface MACs, not per‑port host MACs. The switch will use its MAC(s) when it originates traffic (management traffic, STP BPDUs, LLDP, ARP replies for an SVI, or virtual gateway MACs from HSRP/VRRP). Vendor implementations vary: many devices use a burned‑in base MAC and may derive additional interface MACs from it.

Quick checks and troubleshooting:

# inspect learned MACs (example)
show mac address-table

# inspect a switched virtual interface's MAC (example)
show interface vlan 1

# on a Linux host: view the NIC MAC
ip link show eth0

To observe learning, clear the switch’s dynamic MAC table (vendor command), generate traffic from a single host and watch the entry appear. If a port shows many MACs, it usually means another switch/hub is behind that port.

Bottom line: treat host NICs as the MAC endpoints for switched traffic; switches only expose MACs when they act as endpoints (management, SVIs, control protocols), and exact per‑port MAC behavior is vendor‑specific.

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Member Avatar for CimmerianX

Swtiches will keep a table of mac addresses that are seen on each switch port. If you have 1 pc on a port, then the switch will know that port 1 has the mac for your pc and traffic will only be sent there when destinied for your mac.

You can also cascade switches. If you have a 2nd switch B connected to port 1 on Switch A, then switch A port 1 will have multiple mac addresses on that port once detected. Managed switches also have trunked ports where vlan tagged traffic can be sent across ports with the same end effect, basically.

The switch ports themselves, do not have mac addresses. The switch 'knows' whats macs are to be found on what ports.

commented: It's all handled with the magic of firmware! :-) +13
Member Avatar for rubberman

FWIW, all ethernet interface ports (NIC - Network Interface Controller) have a MAC address. They don't need an IP address since they are only handling traffic at the transmission layer. As I mentioned above, it is the firmware (usually an FPGA or similar device) that deals with where (what MACs) the incoming/outgoing packets are going to be directed to.

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