What's the diff between a router, switch, hub

hi

A router is a device for passing/controlling traffic between seperate physical/logical interfaces.  It routes traffic at layer 3 between networks and is capable of supporting routing protocols which work out the best path for the traffic.

A hub is a layer 2 device that provides port access to several nodes at once - nodes pass traffic by the hub sending arp requests to all ports on the hub and forwards the packets on finding the correct destination

A switch is typically a layer 2 device that works the same as a hub but it has a cam-table where it learns the full table of all arp information of attached devices.  A lookup is performed on the cam-table to direct traffic to the correct destination rather than flooding all ports like a hub.  Some switches also work on layer 3 acting like routers and also support newer functionality like Power over Ethernet, RADIUS 802.1X authentication etc.

An unmanaged switch has the same basic functionality as a switch but does not have the capabililty of having an ip address, working with snmp etc.  Like hubs, they are not typically deployed in larger setups as you cannot see what is happening on the ports/switch engine.

If you google the above in a Q you will get heaps more detail but thats a quick overview

hth

A router links together two logical IP subnets.  For instance 192.168.1.0/24 is on a different network than 192.168.21.0/24.  A router is needed to pass traffic between the two.  A bridge is similar except for that it is used to connect to networks that are in the same IP range.  For instance 192.168.1.0/24 is split between to physical segments.  The bridge is responsible for keeping track of what IPs exist on either side and sending that traffic across as necessary.  The only place you see bridge technology anymore is in wifi to extend a wireless network range.  

A hub is a dumb device in that it doesn't not interfere with traffic.  When one computer transmits data, everything on that network gets that traffic.  

A switch is a much better device than a hub because it keeps a list of the IP addresses at every physical connection.  In this way it can deliver traffic only to the port that it needs to go.  The importance of this is seen with networks that get above 5 or 10 devices.  The more traffic that appears on the network, the more collisions there are, the slower the network gets, exponentially.  

A managed switch gives more control over how to handle the traffic and it will have an interface that you can connect to.  You have to read the features to see what it includes.  A layer 2 switch, which is more expensive, keeps a list of IPs, but also keeps track of the hardware addresses, an arp list.  This allows more control.

Dear Friend;
Those devoce sequence is below.
Hub->switch-> router
               |
    ------------------
   |.                       |
Unmanaged.     Manageable

Hub=repeater. Means that; hub is a layer1 device. It just increase amlitude of signal.

Switch=multiport bridge. All switch operations are called layer2. Layer2 means mac-address control. Eachport of switch knows which mac address is working where. So, if port 1 host speaking with port4 host, other ports can not hear this conversation.

Router is a layer 3 device. L3 means ip operation device. Ip is hyrercical address. Router can decide whoch ip will go to where under which condition.

Manageable/unmanageable switch difference is detail issue. Basicly unmanageable just simle switch. It makes switching according to mac address table.
Manageable switch can decide switching operation result conditions of admin define. It may include some futures as Vlans, qos, mac filtering.  

@Equalizer, the information that you are giving is very much incorrect.  There are layer 2 and layer 3 switches.  As a matter of fact, most switches work on layer 3 with no knowledge of layer 2.  Also, routers work with both layer 2 and layer 3 to accomplish their tasks.  Also, your sequence of devices has no bearing in networking.  Your information is incorrect and misleading.  Sorry to blast you, but I don't want the poster to get confused.  Read the other posts.

@numero_uno, for the most part I agree with what you are saying, but I do have to correct one minor point.  Switches do not technically "segment a LAN into separate networks."  They separate a LAN into separate segments.  It's just a matter of terminology.  

You are excatly incorrect. Some device can called l3 or l4 switch. This means that they are multi port router. Usually router options are enabled by admin. Other means switch router integrated devices. Please before talk market languages, you should read what is the osi model and devices. Who does not know base of network, he is not able to understand integrated devices working technichs.  

@Equalizer: Sorry, you are correct.  I don't say that very often, but I had a momentary lapse.  Layer 3 switches are the less common, more expensive switches because they maintain MAC/IP translation.