#Switch mac address learning mac#
In order to forward the frame, the switch will check if the destination MAC address exists in its address table. First of all, the switch will store the source MAC address of that frame () and the port the frame came from (fa0/2) in its table as a new entry. Let’s now assume that B wants to reply back to A, so the switch now receives a frame from B destined to A. However, since the switch does not find the address of B in its table, it will have to flood the frame to both ports fa0/2 and fa0/3, so both B and C will receive it: So the table will now contain one entry with the information of server A. When the switch receives this frame from A, it will store the source MAC address () and the port where the frame came from (fa0/1) in its table . Let’s assume that the switch receives for first time a frame from A destined to B. In the initial stage, the switch does not know any MAC addresses at all. A basic example is described below of how a switch, connected to three servers, builds its MAC address table and forwards or floods frames. The same will happen if the switch receives a frame with a broadcast/multicast destination address with the difference that this time the destination of the frames is the well-known broadcast/multicast address. This process is called unknown unicast flooding. What happens though when the switch receives a frame with a destination MAC address that is not included in the table? In that case the switch will just broadcast/flood the frame with the unknown destination address to all of its ports (apart from the port where the frame came from). That means that next time the switch receives a frame with this MAC address as a destination, it will know –by looking in its address table- to which port to forward that frame. Every time a switch receives a new frame, it stores the source MAC address of that frame along with the port from where it received it in its table. But how does a switch actually think and take forwarding decisions?Ī switch learns MAC addresses from the frames it receives and then stores this information in an internal table. While the term CAM table is fairly common, for the purposes of this course, we will refer to it as a MAC address table.A switch is a layer 2 device, which means that it processes frames and forwards them based on MAC addresses.
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Note: The MAC address table is sometimes referred to as a content addressable memory (CAM) table. The switch can now forward frames between source and destination devices without flooding, because it has entries in the address table that identify the associated ports.
![switch mac address learning switch mac address learning](https://i.pinimg.com/originals/04/14/de/0414de8f336326918c5a5cea709eb088.jpg)
The destination address of the frame and its associated port is found in the MAC address table. The switch enters the source MAC address of PC2 and the port number of the switch port that received the frame into the address table. The destination device replies to the broadcast with a unicast frame addressed to PC1. Because the destination address is a broadcast, the switch floods the frame to all ports, except the port on which it received the frame. The switch enters the source MAC address and the switch port that received the frame into the address table. The switch receives a broadcast frame from PC1 on Port 1.
![switch mac address learning switch mac address learning](https://zeru.com/blog/wp-content/uploads/How-to-Change-Password-in-Facebook-on-Your-Mac_10659.png)
To see how this works, view each of the steps in Figures 1-6. Typically, switch ports used to interconnect two switches have multiple MAC addresses recorded in the MAC address table. In networks with multiple interconnected switches, the MAC address tables record multiple MAC addresses for the ports connecting the switches which reflect the node's beyond. When the destination node responds, the switch records the node's MAC address in the address table from the frame's source address field. When an incoming data frame is received by a switch and the destination MAC address is not in the table, the switch forwards the frame out all ports, except for the port on which it was received. Once a MAC address for a specific node on a specific port is recorded in the address table, the switch then knows to send traffic destined for that specific node out the port mapped to that node for subsequent transmissions.
![switch mac address learning switch mac address learning](https://benisnous.com/wp-content/uploads/2021/04/DevOps-amp-SysAdmins-Physical-switch-not-learning-MAC-address-of.jpg)
A switch builds its MAC address table by recording the MAC addresses of the nodes connected to each of its ports.
#Switch mac address learning how to#
For a switch to know which port to use to transmit a unicast frame, it must first learn which nodes exist on each of its ports.Ī switch determines how to handle incoming data frames by using its MAC address table. The switch fabric is the integrated circuits and the accompanying machine programming that allows the data paths through the switch to be controlled. Switches use MAC addresses to direct network communications through their switch fabric to the appropriate port toward the destination node.