A network hub is a box with several Ethernet ports that repeats every signal it receives out of all its other ports. It works at layer 1, reads no addresses and makes no decisions, so every connected device shares one collision domain, runs at half duplex and sees everybody else's traffic.
Switches send each frame only to the port that needs it. Hubs are obsolete, and the right response to finding one is to replace it.
- A hub repeats electrical signals. It does not read MAC or IP addresses
- Every device on a hub shares the bandwidth and the collisions
- Hub ports run at half duplex, at 10 or 100 megabits per second
- A small switch is inexpensive and removes all three problems
- The one honest use left is watching traffic, and a mirror port does that better
On this page
The hubWhat a network hub does
A network hub is the simplest device that can connect multiple computers into a local area network. Each device plugs into a port on the hub with a twisted pair cable, which makes the hub the central point of a star topology. That is the whole resemblance to a modern network.
Inside, a hub is a multiport repeater. When an electrical signal arrives on one port, the hub regenerates it and transmits it out of all the other ports. It does not store the data, inspect it or look for a destination.
So a data packet sent from one computer to one printer is delivered to all the devices on the hub, and each network card discards what is not addressed to it. Data transmission on a hub is a broadcast every time, whatever the sender intended.
That puts hubs at layer 1 of the OSI model, the physical layer. A hub has no MAC address table and no idea which device is on which port. An unmanaged hub has no MAC or IP address of its own either. It is closer to a powered cable splitter than to a networking device.
The word gets borrowed for other products: a USB hub and a smart home hub are unrelated devices that share only the idea of a central connection point. On this page, hub means the Ethernet hub.
CollisionsWhy every device on a hub shares one collision domain
Because a hub repeats everything everywhere, all the devices connected to it behave as if they were on one shared wire. Only one of them can transmit data at a time. If two transmit at the same moment, the signals collide, both frames are destroyed and both senders have to try again.
Ethernet handled this with CSMA/CD: listen before sending, detect a collision, wait a random time, send again. That only works at half duplex, where a device either sends or receives. So every port on a hub runs at half duplex, and a device that could send and receive at once is not allowed to.
Three consequences follow, and they are the reasons hubs disappeared.
The bandwidth is shared. A 100 megabit hub gives 100 megabits to the whole group, not to each port. Ten busy devices get a fraction each, minus the time lost to collisions. Network performance falls as devices are added, which is the opposite of what people expect when they add ports.
Collisions grow with load. On a quiet network they are rare. On a busy one, retransmissions create more traffic, which creates more collisions. A hub based network degrades sharply instead of gradually.
Everybody sees everything. Every frame reaches every port, so any connected device running a capture tool can read data meant for the others. That is a network security problem with no fix, because the hub has no settings.
Size was limited as well. Collision detection depends on timing, so 10 megabit Ethernet followed the 5-4-3 rule: at most five segments and four repeaters between any two devices, with only three of the segments populated. Fast Ethernet was stricter, allowing one Class I hub or two Class II hubs in a collision domain.
The switchHow a switch fixed what a hub got wrong
A switch looks the same from the outside: a box of Ethernet ports at the center of a star. The difference is that a switch works at layer 2, the data link layer, and reads the addresses in each Ethernet frame.
It learns which MAC address lives on which port and records that in its MAC address table. A frame for the printer goes out of the printer's port and nowhere else. Each port becomes its own collision domain with a single device on it, so the link runs at full duplex and collisions stop.
In a hub vs switch comparison, that one change removes every hub problem at once. Each port gets the full bandwidth in both directions. Adding devices does not slow the network down. A device sees only its own data plus broadcasts.
Switches also brought features that hubs never had: VLANs to separate multiple networks on one box, port security, access control per port, Power over Ethernet and monitoring.
Price was the only argument for the hub, and it ended in the early 2000s when small switches became as cheap. For any new purchase, the network hub vs switch question has one answer: buy the switch.
Hub typesThe types of hub you may see named
Older networking documentation and exam material divide hubs into types. The labels describe history, not a choice you need to make.
Passive hub. A connection point that joins the wires and passes signals along without regenerating them. It adds no reach to the network.
Active hub. The common kind: it has a power supply and regenerates the signal before repeating it, so each cable run can use its full length. This is the multiport repeater described above.
Intelligent hub. An active hub with a management module, usually SNMP, that reports port status and lets an administrator disable a port remotely. It still repeats data to all the ports.
Dual speed hub. A 10/100 device that contains two hubs, one per speed, joined by a small internal bridge. Devices at the same speed still share a collision domain.
The Gigabit Ethernet standard still defined repeaters, but by then the market had moved to switching. Ethernet at 10 gigabits and faster is full duplex only, with no CSMA/CD, so a hub at those speeds cannot exist.
Still out thereHubs are obsolete, and where you may still meet one
Nobody should install a network hub today. That does not mean you will never find one, and knowing where they hide is the practical value of this page.
Under a desk or in a ceiling. Somebody needed two more ports fifteen years ago and the box is still there. The symptom is a group of devices that are slow only when several of them are busy, and a switch port upstream logging collisions.
Inside old industrial and building systems. Machine controllers, older access control panels and lab instruments may have been installed with a small hub in the cabinet. Replace it with an unmanaged switch unless the equipment vendor says the system depends on every device seeing all traffic.
In a network engineer's bag. Because a hub copies all data to all ports, plugging a laptop into one was the classic way to capture traffic between two devices. A mirror port on a managed switch, or a network tap, does the job without forcing the link to half duplex.
The page on reading a Wireshark capture covers what to do with the data once you have it.
In a product listing. If something new is sold as an Ethernet hub, read the specification. A device that lists full duplex, a MAC address table or gigabit ports is a switch using the old word.
When a hub has to stay connected to a switch for a while, leave the switch port on autonegotiation. It will settle at half duplex, which is correct for a hub. Forcing the switch side to full duplex creates a duplex mismatch and a link full of CRC errors.
PitfallsWhere people go wrong
Calling every small switch a hub. The word survives in speech long after the hardware left. Before troubleshooting a "hub", look at the label. If it is a switch, collisions are not your problem.
Forcing full duplex on a port that faces a hub. A hub cannot do full duplex. The forced side sends whenever it likes, the hub side sees collisions, and throughput collapses while the link light stays green.
Chaining hubs to reach farther. Each added hub enlarges the same collision domain, and the repeater limits exist because late collisions appear when the domain gets too big. One switch ends the problem.
Keeping a hub as a cheap monitoring tool on a live link. It drags that link down to half duplex and shared bandwidth while you measure it, so the capture shows a network that is slower than the real one.
Assuming an old hub is harmless because it still works. It exposes all the traffic on it to every connected device, and it cannot be managed, monitored or secured. Working is not the same as acceptable.
ComparisonHub, switch and router, and what each one does with incoming data
| Criterion | Hub | Switch | Router |
|---|---|---|---|
| OSI layer | Layer 1, physical | Layer 2, data link | Layer 3, network |
| Reads | Nothing | MAC addresses | IP addresses |
| Sends incoming data to | Every other port | Only the destination port | The next network |
| Collision domain | One for all ports | One per port | One per port |
| Duplex | Half | Full | Full |
| Bandwidth | Shared by all devices | Dedicated per port | Dedicated per port |
| Who can see your traffic | Every connected device | Only the destination | Only the destination |
| Place in a network today | None | Connects devices in a LAN | Connects the LAN to other networks |
The hub vs router row matters less than it looks, because the two were never alternatives. A router joins different networks and decides where packets go next. Hubs joined devices inside one network, and that is the job switches took over. The rows on collision domain and duplex explain why.
FAQFrequently asked questions
What is a hub in networking?
A hub is a layer 1 device with several Ethernet ports that repeats any signal it receives out of all its other ports. It reads no addresses, so every connected device shares the same bandwidth and the same collision domain. Switches have replaced hubs.
What is a hub, in simple terms?
A box that joins several computers with cables and copies whatever one of them sends to all the others. Each computer ignores what is not addressed to it. It is simple and cheap, and it wastes capacity and exposes traffic.
What is the difference in hub vs switch?
A hub repeats incoming data to every port and forces half duplex. A switch reads the destination MAC address and forwards the frame to one port at full duplex. The switch gives each device dedicated bandwidth and keeps traffic private.
Network hub vs switch: which should I buy?
A switch, always. Small unmanaged switches are inexpensive, run at gigabit speeds and full duplex, and avoid collisions entirely. There is no performance, security or price reason left to choose a hub for a network.
What is an Ethernet hub?
Ethernet hub is the full name for a network hub: a multiport repeater for twisted pair Ethernet, usually with 4 to 24 ports at 10 or 100 megabits per second. Some older models also carried a coaxial or AUI connector for legacy segments.
What does a hub in computer network diagrams mean today?
In a current diagram it usually means a central connection point in general, or the drawing is old. If a physical hub really is installed, treat it as a fault waiting to be found and plan to replace it with a switch.
What is the difference in hub vs router?
A hub connects devices inside one network by repeating signals at layer 1. A router connects separate networks and forwards packets by IP address at layer 3. They never did the same job, so one cannot stand in for the other.
Are hubs still used?
Rarely, and not by design. They survive in old installations, inside some legacy industrial equipment and occasionally as a quick way to capture traffic. New networks use switches for every connection.
Does a hub have a MAC address or an IP address?
An ordinary hub has neither, because it never sends or receives frames of its own. Intelligent hubs with a management module had an address for that module only. The ports themselves stayed address blind.
Does a hub slow down a network?
Yes. All devices share one pool of bandwidth at half duplex, and collisions waste more of it as traffic rises. A hub that serves two idle devices may go unnoticed. A hub that serves ten busy ones will not.
Can I connect a hub to a switch?
Yes, and it will work. The switch port drops to half duplex and treats everything behind the hub as one shared segment. Leave that port on autonegotiation, and replace the hub when you can.
What is the difference between a hub and a repeater?
A repeater has two ports and regenerates a signal to extend a cable run. A hub is a repeater with many ports. Both work at the physical layer and neither reads addresses.
Can a hub be used to capture network traffic?
It can, because every port receives a copy of all data. It also forces the monitored link to half duplex and shared bandwidth. A mirror port on a managed switch or a dedicated tap gives a cleaner capture.
Keep readingRelated concepts
Read next · Design Star Topology, and Why the Building Decided It The cabling layout hubs brought to Ethernet and switches kept, with what a central device means for failures. Open this next12 min- Switching · 9 min The MAC Address Table, and How to Find Which Port a Device Is On The table a switch builds to send each frame to one port, which is the thing a hub never had.
- Network fundamentals · 10 min Layer 1 Networking, the Physical Layer, and Why It Is Where Most Faults Start What the physical layer covers, from signals and cabling to the devices that never read an address.