1. Subnetting 129.123.7.55 AND 255.255.255.0= 129.123.7.0 129.123.7.148 AND 255.255.255.0=129.123.7.0 129.123.7.0 COMPARED (MINUS) TO 129.123.7.0= 0.0.0.0 129.123.25.77 AND 255.255.255.0=129.123.25.0 129.123.7.0 COMPARED (MINUS) TO 129.123.25.0=0.0.18.0 Since there is a non-zero result, the request must be forwarded to the routed via the gateway address.

2. Subnetting continued Address rangeSubnet MaskGateway 129.123.51.1-62255.255.255.192129.123.51.63 129.123.51.65-125255.255.255.192129.123.51.126 129.123.51.129-189255.255.255.192129.123.51.190 129.123.51.193-253255.255.255.192129.123.51.254 129.123.51.50 AND 255.255.255.192 = 129.123.51.0 129.123.51.70 AND 255.255.255.192 = 129.123.51.64 COMARISON: ABS(0 – 64) = 64, go to router (gateway)

3. Link Layer Ethernet PPP Token rings

4. Link Layer Terms Framing Link Access Reliable Delivery Flow Control Error Detection Error Correction Half and Full Duplex

5. Ethernet Hardware Network Interface Cards Physical Link –Twisted Pair 100 Meter length limit Point to Point –Fiber Expensive Point to Point 2000 meter length limit

6. Error Detection Parity Checks (16 bit example) Data bits:Parity 01110001101010111 One bit even parity Can’t tell which bit is wrong

7. Two dimensional Even Parity 101011101011 111100101100 011101011101 001010001010 Parity OkParity Error Forward Error Correction possible

8. Checksumming (CRC) D. 2 r XOR R D=# of data bits, r = CRC bits Polynomial Code See example on page 429 in book.

9. Multiple Access methods Shared Wire (ethernet) Shared Wireless (WiFi, 802.11a/b/g) Satellite Cocktail party

10. Multiplexing Time division –Each packet has a defined time slot –Requires precise timing Frequency division –Each packet has it’s own frequency allocation –Requires large bandwidth for many channels CDMA (Code division multiple access) –Assigned codes (wireless techniques, Ch. 6)

11. CSMA (carrier sense multiple access) Listen before speaking If someone else begins talking at the same time then stop talking (collision detection).

12. Packet Traffic Network Cable

13. Collisions Signal 1 Signal 2 0 5 0 5 0 10 Sum of 1 and 2 Ethernet threshold

14. MAC (Media access control addressing) 12 digit hexadecimal address Unique to every system on the LAN Usually hard coded into the NIC but can be changed in software Broadcast address ff:ff:ff:ff:ff:ff

15. Address Resolution Protocol (ARP) Translates IP addresses to MAC addresses. Keeps in subnet traffic inside the subnet. Uses timers to clear ARP tables arp –a lists arp entries (PC or Unix) arp –ddeletes an arp entry

16. DHCP Dynamic Host Configuration Protocol Configure many machines from one server at boot. Multiple servers, uses router helper addresses to discover servers. Addresses can be static (same address for every lease period) or Dynamic (different address for each lease period).

17. DHCP Interchange

18. Ethernet Cabling Cont. –Coax (10 MB ethernet only) obsolete inexpensive Bus System (party line) Thin(185 Meter length limit) –30 connections/cable, min 18 inches between Thick (500 meter length limit) –200 connections, min 2.5M between Transceivers

19. 10baseT/100baseT 2 twisted pairs Transmit/Receive 100 meter/328 foot distance limit Uses standard telephone modular plugs Category 3 (10mb) vs. Category 5 (100mb)

20. Twisted Pair Ethernet Ethernet uses wires 1 and 2 for one pair and 3 and 6 for the other pair. Wires 4 and 5 are used for analog (single pair) telephone Ethernet data is transmitted on one pair and received on the other pair in the cable.

21. RJ45 Connector 1 2 3 4 5 6 7 8 Looking from the CABLE end

22. 1 2 3 4 5 7 8 6 White/Orange Orange/White White/Green Green/White Blue/White White/Blue White/Brown Brown/White

23. Ethernet Twist (hub-hub) W/O O/W G/W W/G 1 2 3 6 1 2 3 6 transmit receive transmit receive This can be used to connect two pc’s together

24. Hubs and Repeaters Hubs (Star topology) Twisted Pair Fiber, Coax, Twisted Pair Backbone (Twisted Pair may need a twist!)

25. Hub Advantages Standard Telephone Wiring Standard Punch Blocks and Cross Connects Ability to disable a single port Easier to monitor traffic patterns Visible Indication of Link Status If a wire is cut only one port is affected –Unless the backbone feed is cut!

26. 10/100 Switch 10BaseT hubs Telephone connections

28. Coaxial Installation Multidrop (Bus topology) T T=terminator (50 ohm resistor) Repeater Backbone Other computers T T T

29. Repeater Rule 10MB 3 repeater rule Repeater System 1 Sys 2 Sys3 System 1 can talk to Sys 2 but not Sys3

30. Network Diameter (100MB) 205 Meter Limit Repeater 100M 5M 100M 10MB diameter is 500M

31. Switches and Bridges Repeater Bridge

32. Bridge Insides Interface Filter based on ethernet address LAN A LAN B

33. Switch Insides A B C D E F G Switching based on ethernet address

34. 100baseT to 10baseT Hub/Bridge 10baseT 100baseT 10baseT hub 100baseT hub 100baseT to 10baseT Bridge Module

35. 10MB Ethernet Rules 3 repeater (populated) limit 5 repeater per segment limit 7 bridges per ethernet lan Cable lengths 1024 stations per ethernet lan

36. How to get around limits? Hubs Switch ROUTER Other Lans To the Internet (switching based on IP address) Firewall

37. Ethernet Errors Carrier Loss –Link Lights? Collisions –What does the collision light indicate? Troubleshooting tools –tcpdump, snoop, traceroute, ping

38. Routed vs. Switched Network Routed –IP/IPX Layer Routing –Subnetted Network –Broadcast Filtering –More Expensive –Complex Configuration –Better Control Switched –Ethernet Layer Routing –Flat Network –Broadcasts propagate –Less Expensive –Simple Configuration –Loose Control –Network Diameter limit

39. Token Ring Special packets called tokens circulate in a ring from computer to computer. –If a free token is detected then a computer will take control and send it’s data –If a token is destined for a specific computer that computer takes the token –One one computer at a time can use the token so no collisions take place.

40. Token Ring Mic (Media Interface Connector at each computer) 4 or 16 MB/s

41. MAU Multistation Access Unit `` Ring inRing out Computer Ports

42. PPP Protocol Modem Pools Multiple Network Layer Protocols Multiple types of links Error Detection Failure detection (liveness) Address negotiation Simple

43. Link Layer The End REMEMBER TEST NEXT WEEK!