Differences between Routers, Switches & Hubs

[Stryker]

Hi folks,

Can someone explain to me the differences between Routers, Switches and Hubs? I've done some searching but can't really find a straight foward answer and I know I can always count on PCMECH (a little kissing up there)!

Any explinations would be appreciated,
Thanks,
Stryker

[Jomama]

Simply put, routers and switches keep a list of which connector leads to which IP address, and therefore do not have to broadcast to all connectors. hubs broadcast to all connectors. Hubs therefore, increase network traffic.
The diff between routers and switches is the level at which they work on the TCP/IP protocol.

[mbossman2]

hubs - early form of LAN connection. everyone sees all traffic from everyone. downside: lower performance as you must wait your turn to send.

switches - again a LAN connector. you only see traffic intended for you (identified by your unique MAC address), which really improves performance...you don't have to wait to send and other pc's are wasting cycles looking at and discarding data not meant for them

routers - allows different networks (as ID'd by their IP addresses) to "see" and communicate with each other. without this device the internet would be a whole lot smaller than it is now.


A common misconception: most switches are "layer 2" switches and they do not move (actually switch) traffic based on IP addresses. An L2 switch does not "unwrap" an ethernet frame far enough to access the IP address, the switch "opens" up the frame only far enough to view the destination MAC address. That address is then compared to the CAM table in the switch, which matches up MAC address to physical port. Now switches can be assigned IP addresses that is usually done to identify the switch as a unit for management purposes, a switch will work perfectly fine without an IP address. Now a "layer 3" (aka L3) switch, as it incorporates the key feature of a router (namely the ability to "see" and communicate with other IP networks), has the ability to unwrap an ethernet frame 1 step deeper than an L2 switch and makes its switching and routing decisions based upon both the MAC and IP address. The really cool part of the higher end L3 switches is that they are able to remember that a certain MAC address belongs to a certain IP subnet, so instead of having to "unwrap" every frame of a session it can remember the routing decision thereby giving a big boost in performance. but I digress.

[Mesaeus]

Heheh, thanks for the info mbossman2. Is a L3 switch the same as a "managed switch" ? Oh, and you forgot one important practical consequence of the difference between hubs and (L2) switches (in fact THE most important difference) : if both have 10M/100M/1000M capabilities, on the hub all devices of the same speed will only see each other, while the switch will allow everyone to see each other, no matter what the speed. This is IMHO the most important reason to take a switch over a hub. With a hub, you would have to set every device to the lowest speed denominator (often 10M) for them to all see each other, otherwise the 10M devices would see only each other, the 100M only the other ones with 100M and so...

[Stryker]

Wow some great information here guys!
Thanks for the replies everyone.

[mbossman2]

Originally Posted by Mesaeus Heheh, thanks for the info mbossman2. Is a L3 switch the same as a "managed switch" ?

no, an L3 switch is a switch that has the features of both a router and a switch. that is to say an L3 switch allows for different IP subnets to see and communicate with you. A managed switch OTOH is switch that allows "remote control" and reporting functions from a centrally located management console. IE: you have a company spread across 14 buildings and 17 floors, you need to move 1 user from the accounting VLAN to the HR VLAN (they changed jobs). Without a managed switch, you would have to pack up your laptop, find the switch, plug into the console port and make the changes and go back to your desk. With a managed switch, you can do this all remotely from your office. For most small deployments (1 floor, 1 wiring closet, 1 switch) a managed switch is a luxury item. An L2 switch can be managed or not, an L3 switch is almost always managed as it is a key part of a much larger network where management becomes an improtant feature.

Originally Posted by Mesaeus Oh, and you forgot one important practical consequence of the difference between hubs and (L2) switches (in fact THE most important difference) : if both have 10M/100M/1000M capabilities, on the hub all devices of the same speed will only see each other, while the switch will allow everyone to see each other, no matter what the speed.

that is certainly a good point, the other major reason that switches are preferred over hubs is the elimination of data collisions. the entire hub and all devices connected are a single collison domain whereas with a switch, the collision domain is limited to a single port and the port of the device connected (and even that is elimiated when full duplex is active).