1. Network Devices Lecture 2

2. Cabling Computer to computer – crossover cable Computer to hub – straight-through cable Hub to switch or Hub to hub MDI-X port to MDI port – straight-through MDI port to MDI-X port – straight-through MDI-X port to MDI-X port – cross-over

3. LEDs Light emitting diodes Present on both hubs, switches, and routers Green – live connection at that port on that piece of equipment Flashing green – activity (traffic) Amber – problem Red or no light – not working

4. Managed v. Unmanaged Applies to both switches and hubs Has an interface that can be configured Speed VLANS (switches)

5. Number of Ports Hubs and Switches 8 16 24 32

6. Packet Network HeaderData The protocol data unit that is transmitted over a WAN or between LANs when using a router.

7. IP Address Logical Address or Network Address #.#.#.#

8. Routers Intelligent network device Has CPU built in Determines best path for packet to get to destination Bases decision on IP address Synonyms – logical address, network address Refers to its routing table to make decisions about which port to send the packet Configurable Can connect two LAN segments Can connect a LAN to a WAN AUI ports – notice the transceivers on the second router on the rack. Serial ports to connect LAN to WAN

9. Routable (Routed) Protocols Responsible for sending messages between nodes. IP – Internet Protocol (part of the TCP/IP protocol suite IPX/SPX – Novell – going away; replaced by IP Appletalk – MacIntosh – replaced by IP

10. NetBeui This network protocol is non-routable.

11. Routing Protocols Routing protocols route routable protocols Responsible for updating routing tables between routers so they can know the topology of the network and determine best path. Routing tables – lists of networks and the associated port to each network Routing can be dynamic (automatic) or administrator can configure a static route.

12. Routing Table Example NetworkInterface 192.5.5.0E0 205.7.5.0E1 201.100.11.0S0 S0 Network 201.100.11.1 E1 Network 205.7.5.0 Network 192.5.5.0 E0

13. Routing Protocols Distance Vector Link State

14. Distance Vector Routers send routing table updates to each neighboring router periodically. Examples RIP (Routing Information Protocol) IGRP (Interior Gateway Routing Protocol) Movement from one router to the next is considered a “hop.” DV metric (measurement) is “hops.” Lower number of hops is better – determines best path

15. DV Disadvantage Each router transmits its entire routing table every 30 seconds (RIP) creating a lot of network traffic.

16. Convergence The amount of time needed for all routers in a network to have common knowledge – routing tables all have the same information in them.

17. Routing Loops A C D E B Network 1 At first, all routers have common routing tables. Network 1 goes down. Router E sends its routing table without Network 1. Router A updates its routing table. At the next update (after 30 seconds), Router A sends its table to D and B. They have to update their tables. Meanwhile, Router C doesn’t have the update about Network 1 so it sends its table to D & B. D may assume that there’s another path through C -> B to Network 1 so it updates its table. Next round, it updates Router A. Router A assumes there is another path. Now they all have inaccurate information and the loop continues.

18. Split Horizon A C D E B Network 1 Split horizon will not allow an update from the opposite direction of the first update. So, A notified D and B and they cannot send erroneous tables back to A thereby preventing routing loops.

19. Link State Protocols Examples OSPF – Open Shortest Path First NLSP – Network Link State Protocol When network is installed and OSPF configured as the routing protocol, OSPF uses LSAs (Link State Advertisements) to collect information about the network and build a database of the entire topology. During the initial stage where it is learning the topology, the process causes a lot of activity on the network. After the database is built and best paths chosen, traffic is minimized because updates only occur when there is a topology change, (for example, a network goes down) and LSAs are exchanged to make the update in the database. Disadvantage Requires more RAM to store the database than DV protocols.

20. Server-based Routers Servers can have two NICS installed and act as a limited router.

21. Brouter Device that can function as both a router and a bridge depending upon the protocol of the message. If it is a routable protocol, it routes it. If the message protocol is an Ethernet protocol, it either forwards it or blocks it (functions as a bridge).

22. Gateways A device, system, or software that can perform the function of translating data from one protocol to another (TR to Ethernet), and one format to another. Usually a server. Slows network traffic because of translation time.

23. CSU/DSUs Channel Service Unit/Digital Service Unit Changes signal from one digital format to another.

24. ISDN Terminal Adapters Translates digital signal between two digital formats.

25. Modem Modulator/Demodulator Translates from digital to analog and back. 56 kbps maximum connection speed. Actual transfer speed is less – around 43 kbps.

26. Two Factors that Determine Modem Connection Speed Maximum connection speed of the Universal Asynchronous Receiver/Transmitter (UART) chip Actual modem speed

27. UART Chips & Speeds ChipSpeed bps 82509600 16450115200 16550115200 16650430800 16750921600 16950921600

28. Modem Commands to Know ATA – Answers incoming call ATH – Hangs up current connection ATZ – Resets the modem ATI3 – Displays modem id info