question about bridge

bighornsheep

I remember that with switches, they look at the source address first, and if there isnt a record of the MAC, it records it, and then proceed to looking for the destination MAC, and if it doesnt exist, it floods it to all the ports...

Am I right? is this also the case with bridge?

Technotes only mentions that it reads the incoming frame...and my Network+ book didnt mention this detail...or maybe I havent read far enough yet...

netcom2000

A switch provides many collision domains which are good on networks bandwidth, say computer A wants to send data to computer X on the network, then only computer X will recieve the frame, so if you have a 24 port switch for example then no other node on the network will be affected.

This means that on a 24 port switch there are 24 collision domains.

A bridge on the other hand, (though you wont see many about in networks today) builds a table based on MAC addresses, so if you have a network of 10 computers, five on one side of the bridge (or interface) and five on the other, when a computer sends data, the bridge checks its physical address table, and if the data is destined for a computer on the other side of the bridge, it will send it there, if on the other hand the data is destined for a computer on the same segment, then that computer will get the data without having to look at the other segment.

Dont confuse bridges with routers though, bridges work at the second layer of the OSI model, and deal only with MAC (Hardware addresses) whereas a router looks at the logical address (IP) and forwards it to other routers and default gateways.

Hope this helps, takes time, but keep at it and it all falls intoplace.

bighornsheep

ah.....

right! ...bridge vs. router...
thanks!

Danman32

Bridges and switches are essentially the same. Bridges are often thought of as having only 2 ports where switches have multiple ports.

I believe a switch/bridge looks at the destination address first, so it can begin to forward to the correct port. As it forwards, it can get the source address and record the port it is on if it isn't already in the table.
If you reversed this, then the forwarding would be unnecessarily delayed. Granted in a single process hardware if you defer the source address store after forwarding, you only delay processing the next frame, but I am sure hardware is optimized that the storage of the source MAC can be processed while beginning processing the next frame.