Switch – Does a Switch MAC Address Table Sync Across VLANs?

broadcastmac addressswitchswitchingvlan

Ok, I have read up about this 16K limit for the MAC address table, or better known as the CAM table, on certain switches. Lets say I have 14 different edge switches with that 16K limit, and I have VLAN 200 set up across all of these same switches, would I expect to see the tables "sync" across all of the switches for that VLAN? For example, if one switch fills up with 10K mac addresses, would I expect to see these same MAC addresses in the CAM table across all switches in that VLAN? Could this be something that differs by configuration and/or vendor implementation?

Best Answer

Synchronizing MAC address tables across switches doesn't make any sense. Each switch maintains its own MAC address table.

For instance, suppose you have Switch 1 and Switch 2 connected together of their ports 24, and MAC address 0123.4567.89ab comes into Switch 1 port 5. On switch 1, the MAC address table would reflect that MAC address 0123.4567.89ab is connected to port 5. If any frames from the host with that MAC address find their way to Switch 2, the MAC address table of Switch 2 will have MAC address 0123.4567.89ab coming into port 24. If no frames from MAC address 0123.4567.89ab get sent to Switch 2, then Switch 2 will not have 0123.4567.89ab in its MAC address table.

If you synchronize MAC address table across those two switches, then how would you propose to resolve the port conflict where 0123.4567.89ab is on port 5 of one switch, but it is on port 24 of the other switch?

The closest thing you could have is with switch stacks, where multiple switches are connected in a stack, and the stack looks like a single switch. You configure the stack, not the individual switches, and things like STP and MAC address tables are done as if the stack was a single switch.

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