#Layer 2 mac address learning for mac

A layer 2 switch uses Content Address Memory to keep track of the source MAC address. For example, if server 1 sends traffic to server 3, it does not get broadcast onto the link to switch C, only on the link to switch D. While doing this, it requires the MAC address of a NIC on each network node and learns these MAC addresses, and maintains them in a table called a MAC table. This way, traffic between any two switches is not broadcast to the other switches. Other hosts using the forged MAC address of Host A cannot obtain the frames destined for Host A.įor example, in the following topology, switch A learns the MAC addresses of ports on switch B, C, and D. Then, the frames destined for Host A are always sent out of port A. To improve the security for Host A, manually configure a static entry to bind Host A to port A.

especially, switches make decisions to forward and filter frames, learn MAC addresses, and use STP to avoid loops, as follows: Step 1.

#Layer 2 mac address learning for mac

Forwards frames destined for MAC A out of port B to the illegal user.Īs a result, the illegal user obtains the data of Host A. Switches use Layer 2 logic, examining the Ethernet data-link header to choose the way to process frames.Learns a new MAC address entry with port B as the outgoing interface and overwrites the old entry for MAC A.When an illegal user sends frames with MAC A as the source MAC address to port B, the device performs the following operations: When Host A is connected to port A, a MAC address entry will be learned for the MAC address of Host A (for example, MAC A). Mac-address-table age-time), after which they are automatically deleted.ĭynamic MAC address learning does not distinguish between illegitimate and legitimate frames, which can invite security hazards. Dynamic entries remain in the table for a predetermined amount of time (defined with the command If the retrieved address does not exist in the table, it is added. Network nodes with multiple network interfaces, such as routers and multilayer switches, must have a unique MAC address for each NIC in the same network. Dynamic: Dynamic entries are automatically added to the table through a process called MAC learning, in which the switch retrieves the source MAC address (and VLAN ID, if present) of each Ethernet frame received on a port.Static entries remain active until they are removed by the switch administrator. Static entries have higher priority than dynamic entries. Static: Static entries are manually added to the table by a switch administrator.The MAC address table can contain two types of entries: The table enables the switch to send outgoing data (Ethernet frames) on the specific port required to reach its destination, instead of broadcasting the data on all ports (flooding). The MAC address table is where the switch stores information about the other Ethernet interfaces to which it is connected on a network.