Switch vs Router Key Differences | Generated by AI
You’re very close to the core difference, but let’s clarify it accurately and cleanly.
Key Differences Between a Switch and a Router
| Feature | Layer | Switch (Network Switch) | Router |
|---|---|---|---|
| Operates at | OSI Layer | Layer 2 (Data Link) – sometimes Layer 3 (multilayer switches) | Layer 3 (Network layer) |
| Uses | MAC addresses (Ethernet hardware addresses) | IP addresses (logical network addresses) | |
| Needs to know destination in advance? | No – learns automatically via MAC address table | Yes – needs routing table (static or dynamic) | |
| Main job | Forward frames inside the same network (same subnet) | Forward packets between different networks/subnets | |
| Broadcast domain | One switch = one broadcast domain (unless VLANs) | Each interface = separate broadcast domain | |
| Typical purpose | Extend a LAN, reduce collisions, high-speed local connectivity | Connect different LANs, connect to Internet/WAN |
How They Actually Work (Simplified)
Network Switch
- When a frame arrives, the switch looks only at the destination MAC address.
- It maintains a MAC address table (CAM table) that it learns automatically:
- “MAC 00:11:22:33:44:55 was seen on port 5” → next time it sends traffic for that MAC only to port 5.
- It never changes the source or destination MAC address (except in very rare cases). It just forwards the original frame to the correct port.
- All devices connected to the same switch (same VLAN) are in the same IP subnet and same broadcast domain.
- Goal: make a bigger, faster Layer-2 network.
Router
- When a packet arrives, the router looks at the destination IP address.
- It checks its routing table: “To reach 192.168.2.0/24, send it out interface Gi0/1, next-hop 10.0.0.2”.
- The router rewrites the Layer-2 information:
- Changes destination MAC to the next-hop’s MAC (or the final destination if directly connected).
- Changes source MAC to its own MAC on the outgoing interface.
- Decrements TTL, recalculates IP checksum, etc.
- Routers separate different IP networks and broadcast domains.
- Goal: connect different networks together (including the Internet).
Your Statements – Corrected
You said:
“route, you need to know destination, have route table to route, where to route”
→ Yes, 100% correct.
“while switch is easy, because like switch packet, just the target are fixed, just need to change source and target”
→ Almost, but not quite:
- The switch does not change source or destination MAC addresses (normally).
- The “target” (MAC) is not fixed forever; the switch learns dynamically which port each MAC is on.
- It’s “easy” because it only cares about MAC → port mapping inside one network.
“switch packets, it is to extend the network instead of routing, right?”
→ Exactly right. A switch extends a single Layer-2 network (makes it bigger and faster). A router connects multiple different networks.
Quick Analogy
- Switch = local post office sorting letters inside the same city by street address (MAC).
- Router = the highway system that moves mail between different cities using zip codes (IP).
So yes, you got the big picture right: switches make one network bigger, routers connect different networks together.