MAC Address Tables In Switch For Network Data Forwarding

MAC Address Tables

Ethernet switches store MAC Address Tables, also known as Content Addressable Memory (CAM) tables. Monitoring switch ports and MAC addresses to efficiently forward Ethernet communications is its key purpose. According to the OSI model, it functions at the Data Link Layer (Layer 2).

The operation of MAC Address Tables is broken down as follows:

How it Works

Learning Mode

The switch looks at the frame’s source MAC address when an Ethernet frame reaches it. It then enters this MAC address into its MAC Address Table together with the actual port number where it was received. We call this process MAC learning. The switch gradually creates a dynamic directory of all the devices that are currently in use together with their locations.

Forwarding Mode

The switch verifies the target MAC address upon receiving a subsequent frame.

• The switch only delivers the frame to the specified port if the destination MAC address is present in the table. Unicasting is a type of tailored forwarding that greatly lowers superfluous network traffic and boosts efficiency.
• The switch floods the frame to all ports (apart from the port it originated from) if the target MAC address is not present in the table. It keeps flooding until the right route is found and understood.

Ageing and Table Management

The MAC Address Table contains temporary entries. Ageing timers are used by switches to keep the table from getting full or out of date. A device’s entry is automatically deleted from the table if it does not transmit any traffic for a predetermined amount of time (for example, by default, about 300 seconds). This keeps the table current and helps save memory.

Types of Entries

A MAC Address Table has two different kinds of entries:

• Static Entries: The switch administrator manually adds them to the table. Until the administrator removes them, they are active and have a greater priority than dynamic entries.
• Dynamic Entries: When the switch receives an Ethernet packet, these are immediately added via the MAC learning process. If no traffic is identified from the device after a predetermined amount of time, they are automatically deleted.

Structure of a MAC Address Table

Specific fields that describe the connection between MAC addresses and switch ports make up a standard MAC Address Table. A sample structure consists of:

• MAC Address: A device’s distinct hardware identification.
• Port: The actual switch port that the gadget is attached to.
• Age (seconds): The amount of time since a dynamic entry’s last activity.
• VLAN: The Virtual Local Area Network ID that the MAC address entry is associated with, if applicable.
• Type: Indicates if the MAC address was dynamically or statically learnt.

Example of a MAC Address Table:

Here, the switch knows that:

• Device A (MAC AA-AA-AA…) is on Port 1
• Device B (MAC BB-BB-BB…) is on Port 2
• Device C (MAC CC-CC-CC…) is on Port 3

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Advantages of MAC Address Table

MAC Address Tables are necessary for network operation for a number of important reasons:

• Effective Frame Forwarding: By allowing switches to route Ethernet frames to the appropriate port, they eliminate the need to transmit data throughout the network.
• Increased Network Efficiency and Decreased Congestion: They avoid network segments becoming overwhelmed by reducing superfluous broadcast traffic by sending unicast traffic straight to its destination.
• Network segregation: By enabling logical traffic segregation, even on common physical networks, support for VLAN tagging helps avoid data collisions.
• Optimal capacity Usage: By restricting broadcasts, network capacity is better utilised for critical data traffic.
• Easier Troubleshooting: By mapping devices to particular ports using commands (such as show mac address-table on Cisco devices), network administrators can make troubleshooting easier.

Disadvantages

MAC Address Tables have disadvantages despite their advantages:

• Table Overflow: The table’s capacity may be exceeded in big or incorrectly segmented networks, resulting in more broadcast flooding and unsuccessful lookups.
• Vulnerabilities: Malicious attacks like MAC flooding, which overwhelms the table with fictitious entries, or MAC spoofing, which impersonates genuine devices, can target them and damage the network.
• Monitoring Requirements: To avoid errors that over time may impair network performance, regular monitoring is required.

MAC Address Table vs ARP Table

The Address Resolution Protocol table (ARP table) and the MAC address table have separate functions and function at different OSI model layers, despite the fact that both are utilized for address mapping.

MAC Address Table

• Layer: Layer 2 Data Link Layer
• Its function is to associate a physical switch port with a device’s MAC address.
• It is located within a network switch.
• Function: Makes frame switching in a local network more effective.

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ARP Table

• Layer: Layer 3: Network Layer
• Its function is to translate a device’s physical MAC address to its logical IP address.
• Location: resides on a router or host device.
• Function: Converts IP addresses to MAC addresses in order to properly encapsulate a frame for transmission across a local network.

A switch is informed by the MAC address table “which port to send this frame out of,” whereas a computer or router is informed by the ARP table “what MAC address belongs to this IP address.”