Hub, Switch, Router: What Each One Actually Does
Three grey boxes with eight ports each, and from the outside you cannot tell them apart. Put the same frame into each one and three different things happen: the hub copies it out of every port, the switch sends it out of exactly one, and the router opens it, reads the address inside and sends it to another network. This lesson opens the hardware series: what each box actually does, why the hub is gone, what a switch writes on its clipboard, and the two words the exam counts.
You'll learn
- The hub: a Layer 1 repeater that copies every frame out of every port, one shared road, collisions, and why nobody installs one any more
- The switch: it reads MAC addresses, learns source addresses into its MAC address table, floods unknown destinations once, then delivers to one port
- Why a switch still copies one frame everywhere: the broadcast (FF:FF:FF:FF:FF:FF)
- The router: the first box that opens the frame, routes on the IP address, rebuilds the frame for the next network, and never passes a broadcast on
- Collision domains and broadcast domains, and how to count them the way exam questions expect
- The home router: a switch, a router and a wireless access point (plus NAT) in one box
- The Layer 3 switch: a switch with a small routing table, routing between VLANs without a router
- The real thing: a switch's MAC address table and the host's arp -a
- Exam corner: counting broadcast and collision domains across a router, two switches and a hub
Chapters
- 0:00Three grey boxes, one crate
- 0:37The crate, and the roundabout
- 1:13One shared road: collisions
- 1:41The switch-depot and its clipboard
- 2:39The one crate it still copies: the broadcast
- 2:57Where the street ends: the router
- 3:28Collision domains and broadcast domains
- 4:07The box under your TV: three in one
- 4:39The Layer 3 switch
- 5:01The real names
- 5:39The real thing: the MAC address table and arp -a
- 6:10Exam corner
- 6:46Recap and next time
Exam objectives: CompTIA Network+ N10-009: 1.2 (routers, switches, Layer 3 capable switches, hubs, wireless access points), 2.1 (switching concepts: MAC address table, flooding, broadcast and collision domains), 5.5 (arp).
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