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2.2.1. Switching and Routing Appliances
| Appliance | Layer | Function | Decision Based On |
|---|---|---|---|
| Hub | 1 | Repeats signals to all ports | Nothing—blind repetition |
| Switch | 2 | Forwards frames to correct port | MAC address (CAM table) |
| Router | 3 | Forwards packets between networks | IP address (routing table) |
| L3 Switch | 2-3 | Switches within VLANs, routes between | MAC (intra-VLAN), IP (inter-VLAN) |
| Firewall | 3-7 | Filters traffic based on rules | IP, port, protocol, content |
| Load Balancer | 4-7 | Distributes traffic across servers | Algorithm (round-robin, least connections) |
Router: Examines the destination IP and consults its routing table to determine the next hop. Routers create network boundaries—devices on different interfaces are on different networks and need Layer 3 routing to communicate.
Switch: Learns which MAC addresses connect to which ports by examining source MACs of incoming frames. Then forwards frames only to the port where the destination MAC exists. Unknown destinations are flooded to all ports; known destinations go only to the correct port.
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Written byAlvin Varughese
Founder•18 professional certifications