Layer-2 MAC Tables
Network Switches and Access Points connect Hosts on the same Local Network and move traffic according to information stored in their MAC Table.
Also known as the Content Addressable Memory, or CAM table, the MAC Table keeps track of the interfaces or Ports on which a given MAC Addresses can be reached.
For example, a Frame arrives on Switch Port 1 with the Source MAC of Host A.
After UPDATING the MAC Table with Host A’s MAC on Port 1, the Switch will take one of three actions regarding the Frame.
If the Destination MAC is already mapped to a certain Port, then the Switch will FORWARD the Frame to that particular Port, and only that Port.
If however, no entry exists in the MAC Table for the Destination MAC, then the Switch will FLOOD the Frame out all Local Ports, except the Port on which the Frame was received (so as to avoid loops in the Network).
A Switch will also FLOOD should the Layer-2 Broadcast Address be used as the Destination MAC Address.
As source traffic begins to populate on the network, the Switch continues to update its MAC tables in order to forward traffic, rather than flood.
Lastly, a Switch may also FILTER the Frame according to its Destination and/or Source MAC Address, when the Switch is configured with a MAC Access Control List, or ACL, for short.
The Forward Information Base, or FIB for short, allows a Router to look up the interface on which it forwards a Packet received on a different Interface.
The source & destination MAC addresses in the Layer-2 Frame are rewritten in order to enable traffic to pass across each Local Segment, when moving data across networks.
In this way, the MAC table only fills with Layer-2 addresses, that is, addresses belonging to Hosts and interfaces inside the LAN.
44:33:4A:7D:FD:84
A1:8E:09:3A:DC:2C
12:E6:95:77:E8:B6
BF:C9:BB:3B:9C:7B
70:1D:89:7C:FE:3D
38:FD:E1:0D:D2:29
Whenever a Host needs to reach another Host on a different network, it sends the Frame to its Local Gateway.
At Layer-2, the Destination MAC is the Gateway, but at Layer-3, the
At Layer-2 destined to a host on a different Network which it determines according to MAC entries in its FIB, and rebuilds the Layer-2 Frame
Local Interface on a rebuilt Frame will be forwarded to reach the intended recipient.
source
mac address
