Hi,

what do these do and when are these used;

routers
switches
hubs

Thanks in advance.

Sounds to me like you want to google for a network hardware tutorial for detailed info...

Hubs and switches are very similar. A hub simply repeats any ethernet frames that come in on a port to all the other ports (including the one that the frames came in on). It's literally a repeater, all the ports are effectively connected all the time. This means that only a single machine can transmit data at any time, regardless of its destination.

A switch is a bit more intelligent. It looks at the ethernet frame that's arriving and uses it's destination (from the MAC address) to decide which ports to connect together (hence the name switch) so only the destination machine receives the frame. This has the advantage that multiple machines can talk through the switch at the same time, you can have full-duplex communication, and its more secure as not everyone 'sees' all the network traffic.

Routers typically work at a higher level than hubs/switches. (In the case of IP) They make a decision about what to do with the IP packet that arrives on one interface based on things like the destination IP address (most commonly) and possibly the source IP address or TOS flags. Typically they just forward packets to somehwere else, although sometimes they will drop packets, or send errors back to the source of the packet to indicate say a network failure.

Typically hubs/switches are used to connect machines together that are on the same subnet, routers are used inbetween subnets.

that make any sense?

cheers

Jamie...