1. Day11 Devices/LAN/WAN

2. Network Devices Hub Switches Bridge Router Gateway

3. Hub Keyword: Dumb Operates at physical layer –Just repeats electricity Will often cause collisions More machines = more congestion No longer exist

4. Bridge Originally to connect 2 LANs. Selectively forwards packets from one LAN to the other if they are destined for a machine on the second LAN Requires a small computer to evaluate each packet to see where to send it No longer exist

5. Hub Switch Sends traffic to all ports Very cheap Very simple Could connect 8, 16, 24, 32, 64, or 128 computers Could only support a single media (Cat5) Will have lots of collisions Everyone sees everything Only forwards traffic to the port it should go More expensive More complex Can connect 8, 16, 24, 32, 64, or 128 computers Often supports more than one media (fiber, Cat5 etc) Cuts down on collisions You can only see data destined for you

6. Why break up into LANs? A company with 1000 computers could have a single LAN –With hubs, it would be horribly slow –Even with switches, it’ll be fairly slow, you may saturate the backbone of the switch and the switch interconnects Better to break up into 5 LANs with 200 computers each. –Provides less “chatter” –May improve security

7. Physical Breakup Computers 1-200 plug into 7 32port switches Switches connect to each other with fiber People in this LAN can talk to any of the other 199 computers on this LAN They cannot talk to computer 201 which is in our second LAN. LAN1 and LAN2 are both connected to a Router –A single router will be sufficient for all 1000 computers, and will end up with 5 cables connected to it

8. Virtual Breakup Sometimes keeping up with all those wires is difficult –Sometimes 2 people need to be in the same LAN, but are in different buildings Instead of running the wires separately, most switches are smart enough today to deal with Virtual LANs A Virtual LAN (VLAN) acts like a physical LAN, but is created by telling the switch which VLAN each port is on. –Hence, 2 people plugged into the same switch may not be able to talk to each other if they are on different VLANs without going through a router.

9. Router Connects multiple LANs Single connection into network –You don’t plug computers into routers directly Has IP address on network Routes data at a higher level in OSI HUB Computer HUB Computer HUB Computer HUB Computer Router I

10. Switches Routers Used to connect multiple computers locally Decide which machine to send to based on MAC address Used to connect multiple LANs Decide which machine to send to based on IP address Strips MAC address information from the packet and replaces with WAN info

11. Gateway Old term for a device which connects 2 different types of networks –E.g. Ethernet -> Token Ring Today term is usually interchangeable with Router

12. Then and Now In the old days –Computers connected to Hubs –Hubs were interconnected via Bridges/Gateways –When you needed to get to a WAN you passed through a router Today –Hubs and Bridges no longer exist, and have been replaced by switches –Routers are still routers, but are sometimes called gateways

13. Fault Tollerance Networks need to be fault tolerant –If a switch fails, we still want to be able to reach the computer –Solutions: Plug the computer into 2 different switches Make each switch have internal redundancy –If a part of the switch fails, there is a redundant “hot spare” available.