hubs, switches, routers

I was asked to take a look at a wireless seismic network that was slow. The network had about 30 nodes. Several of the nodes were configured as access points, several as backbones and all of them in bridge mode. I suspect that most radios in the 2.4 and 5.8 GHz range come configured out of the box as bridges and for small installations this is no big deal. Every radio sees all of the data from every other radio! What a mess!

When I suggested that the solution was to route everything they said no way it would take to long to learn and take way too long to implement. So they decided to make do with the slow network. I warned them that at some point they would add one more node and the system would just crash.

They did ask me to explain what the difference was between a hub and a router. Here is what I told them:

Wireless Access Points (AP) are wireless hubs and bridged backbones just connect Wireless APs together. When you use your modern wireless radios use them in router mode. Make your network IP aware. Send data only where data needs to go! At OSOP, we maintain a fast private wireless network with about 300 radios all of them routed!

Here is what hubs, switches and routers do:

(By the way, you can configure your fancy wireless router to work just like a hub :)

Hubs

– All a hub does is transfer data to every port excluding the port from where data was generated
– Hubs have no sense of Mac address or IP
– Hubs are half duplex meaning they can only send or receive
– If more than one device sends out data simultaneously then data collisions happen
– In case of a collision, a hub rejects data from all the devices and signals them to send data again. Hubs are prone to collisions and as more and more devices are added to the set up of multiple hubs, the chances of collisions will increase and hence the overall performance of network will go down.
– Nobody uses hubs much any more and with good reason

Switches

– Switches know about MAC addresses, but don’t know about IP
– The reason switches are known as “intelligent hubs” is that they build address tables in hardware to keep track of different hardware addresses and the port to which each hardware address is associated
– Switches, unlike hubs, support full duplex data transfer communication for each connected device

Routers

– Routers know about IPs
– Routers have the capability to forward data across networks
– Sometimes routers are also known as “layer-3 switches”
– Routers maintain routing tables for data forwarding

Everyone should be routing! Send data where data needs to go and NO WHERE ELSE!

— Angel

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