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Differentiate between Layer 2 and Layer 3 switching.

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Layer 2 (Data Link Layer) and Layer 3 (Network Layer) switching are two different approaches used in networking to forward packets at different levels of the OSI model. Let's delve into the technical details of each:

Layer 2 Switching:

  1. Operating Layer:
    • Position in the OSI Model: Layer 2 switches operate at the Data Link Layer (Layer 2) of the OSI model.
    • Functionality: They primarily deal with frames and use MAC addresses to make forwarding decisions.
  2. Addressing:
    • Address Type: Layer 2 switches use MAC (Media Access Control) addresses to forward frames.
    • Address Table: These switches maintain a MAC address table (also known as a forwarding table or content addressable memory - CAM table) to associate MAC addresses with corresponding switch ports.
  3. Forwarding Decision:
    • Basis of Decision: The decision to forward a frame is based solely on the destination MAC address.
    • Broadcast Handling: Layer 2 switches forward broadcasts and unknown unicast traffic to all ports in the same VLAN.
  4. Network Segmentation:
    • Segmentation Capability: Layer 2 switches can create multiple broadcast domains by separating ports into different VLANs.
    • Isolation: Devices within the same VLAN can communicate with each other, but devices in different VLANs cannot without the assistance of a router.
  5. Protocols:
    • Protocols Supported: Common Layer 2 protocols include Ethernet, IEEE 802.1Q (VLAN tagging), and others.

Layer 3 Switching:

  1. Operating Layer:
    • Position in the OSI Model: Layer 3 switches operate at the Network Layer (Layer 3) of the OSI model.
    • Functionality: They deal with packets and use IP addresses for forwarding decisions.
  2. Addressing:
    • Address Type: Layer 3 switches use IP (Internet Protocol) addresses to make forwarding decisions.
    • Address Table: They maintain a routing table, which contains IP addresses and associated next-hop information.
  3. Forwarding Decision:
    • Basis of Decision: The decision to forward a packet is based on the destination IP address.
    • Broadcast Handling: Layer 3 switches typically do not forward broadcasts; they rely on routers to handle broadcast traffic.
  4. Network Segmentation:
    • Segmentation Capability: Layer 3 switches can segment networks into different subnets.
    • Isolation: Devices in different subnets cannot communicate directly without the help of a router.
  5. Protocols:
    • Protocols Supported: Common Layer 3 protocols include IP, OSPF (Open Shortest Path First), RIP (Routing Information Protocol), and others.

Comparison:

  • Operational Scope: Layer 2 switches operate at a lower level, dealing with local network communication, while Layer 3 switches operate at a higher level, enabling inter-subnet communication.
  • Forwarding Decision Basis: Layer 2 switches use MAC addresses, while Layer 3 switches use IP addresses.
  • Broadcast Handling: Layer 2 switches forward broadcasts within the same VLAN, whereas Layer 3 switches generally do not handle broadcasts and rely on routers.
  • Network Layer Functions: Layer 3 switches can perform routing functions, making them capable of inter-subnet communication, unlike Layer 2 switches.