Latest

Home / AR / ccna / MAC / CCNA: MAC Address Table

CCNA: MAC Address Table

June 25, 2024 , ,

CCNA: MAC Address Table

Layer 2 Switches use the MAC address table to make forwarding decisions. This table is populated automatically when a switch receives a frame on a port. As a frame is received on a port, its source MAC address is noted. Let’s try to understand how this works in this article.

A switch that you just powered up, has nothing in the MAC address table. Then PC-1 wants to communicate with PC-2. The switch receives the frame from PC-1 that contains the MAC address 80::01 on port 1. Port 1 is configured as a member of VLAN-11. All this information, the MAC Address, Port Number, and VLAN ID are stored in the switch MAC address table. So in short MAC address table maps the MAC address to the Switch’s VLAN and port and this entry is referred for forwarding decision.

CCNA: MAC Address Table

At this port switch has only one entry in the table. The switch doesn’t know where to forward the frame to other devices like 80::02, so it floods the frame out of all other ports in VLAN-11. All other connected devices in VLAN-11 receive the frame and check the destination MAC address of the frame. All of them except once accept the frame as the destination MAC address matches with its own MAC address and the rest all drop this frame.

PC-2 says “Hey this frame belongs to me and I’ll respond to this frame”. PC-2 responds to PC-1 using its MAC address as the source MAC and the original frame’s source address as the destination MAC address. The switch receives this frame and knows the MAC address of the PC-2 from this response.

CCNA: MAC Address Table

This way, the switch builds the table entries automatically when it sees a frame on a port. The switch now knows the destination MAC address (80::1) is on port 11 and forwards the frame to port 11.

I hope you find this informative!

Continue Reading...