CCNA 200-301 Switch Concepts
CCNA 200-301 Switch Concepts
Understanding Layer 2 & Layer 3 Switches
Layer 2 Switches: The Local Network Organizers
Operating at the Data Link Layer, a Layer 2 switch is the foundational building block of a local network (LAN). Its main job is to intelligently forward data frames to the correct device within the same network or VLAN.
MAC Address Forwarding
Builds a MAC address table to send frames only to the port of the intended recipient device, not to all devices.
Collision Domain Segmentation
Each switch port is its own collision domain, drastically reducing data collisions and improving network efficiency.
Single Broadcast Domain
By default, broadcasts are forwarded to all ports. VLANs are needed to create multiple broadcast domains on a Layer 2 switch.
Analogy: Think of a Layer 2 switch as a smart mail sorter in an office building. It knows exactly which desk (MAC address) each piece of mail (data frame) goes to, so it doesn't have to shout out to the whole floor.
Layer 3 Switches: The Network Navigators
A Layer 3 switch (or multilayer switch) does everything a Layer 2 switch can do, but adds routing capabilities from the Network Layer. It can make forwarding decisions based on IP addresses, allowing it to connect different networks.
IP Address Routing
Maintains a routing table to forward packets between different subnets or VLANs, acting like a high-speed router.
Inter-VLAN Communication
The primary device used for routing traffic between different VLANs without needing an external "router-on-a-stick".
Broadcast Domain Boundary
Naturally stops broadcasts at the network edge, as it does not forward broadcast packets between different networks (VLANs).
Analogy: Think of a Layer 3 switch as the central post office for a city. It not only sorts mail for its own building but also knows how to route mail to different neighborhoods (VLANs) across the city (the entire network).
At-a-Glance Comparison
| Feature | Layer 2 Switch | Layer 3 Switch |
|---|---|---|
| OSI Layer | Layer 2 (Data Link) | Layer 2 (Data Link) & Layer 3 (Network) |
| Forwarding Decision | Based on Destination MAC Address | Based on Destination IP Address (and MAC) |
| Address Table | MAC Address Table (CAM Table) | MAC Address Table & Routing Table |
| Inter-VLAN Routing | No | Yes |
| Broadcast Domains | One large domain (by default) | Multiple, separated domains (one per VLAN/subnet) |
