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Subnetting

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

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Subnetting

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  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 range Subnet Mask Gateway 129.123.51.1-62 255.255.255.192 129.123.51.63 129.123.51.65-125 255.255.255.192 129.123.51.126 129.123.51.129-189 255.255.255.192 129.123.51.190 129.123.51.193-253 255.255.255.192 129.123.51.254 129.123.51.50 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 • 0111000110101011 1 • One bit even parity • Can’t tell which bit is wrong

  7. Two dimensional Even Parity 10101 1 10101 1 11110 0 10110 0 01110 1 01110 1 00101 0 00101 0 Parity Ok Parity Error Forward Error Correction possible

  8. Checksumming (CRC) D. 2r 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 5 Signal 1 0 5 Signal 2 0 10 Sum of 1 and 2 0 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 –d deletes 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 White/Orange 2 Orange/White 3 White/Green 4 Blue/White White/Blue 5 6 Green/White 7 White/Brown 8 Brown/White

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

  24. Hubs and Repeaters • Hubs (Star topology) Twisted Pair Backbone Fiber, Coax, Twisted Pair (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. 10/100Switch 10BaseThubs Telephone connections

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

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

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

  30. Repeater Repeater Repeater Repeater Switches and Bridges Bridge

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

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

  33. 100baseT to 10baseTHub/Bridge 10baseT 100baseT 100baseT to 10baseT Bridge Module 100baseT hub 10baseT hub

  34. 10MB Ethernet Rules • 3 repeater (populated) limit • 5 repeater per segment limit • 7 bridges per ethernet lan • Cable lengths • 1024 stations per ethernet lan

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

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

  37. 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 Routed vs. Switched Network

  38. 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.

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

  40. MAU • Multistation Access Unit `` Ring in Ring out Computer Ports

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

  42. Link Layer The End REMEMBER TEST NEXT WEEK!

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