Subnetting AND = AND = COMPARED (MINUS) TO = AND = COMPARED (MINUS) TO = Since there is a non-zero result, the request must be forwarded to the routed via the gateway address.

Subnetting continued Address rangeSubnet MaskGateway AND = AND = COMARISON: ABS(0 – 64) = 64, go to router (gateway)

Link Layer Ethernet PPP Token rings

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

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

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

Two dimensional Even Parity Parity OkParity Error Forward Error Correction possible

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

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

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)

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

Packet Traffic Network Cable

Collisions Signal 1 Signal Sum of 1 and 2 Ethernet threshold

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

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

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).

DHCP Interchange

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

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)

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.

RJ45 Connector Looking from the CABLE end

White/Orange Orange/White White/Green Green/White Blue/White White/Blue White/Brown Brown/White

Ethernet Twist (hub-hub) W/O O/W G/W W/G transmit receive transmit receive This can be used to connect two pc’s together

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

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!

10/100 Switch 10BaseT hubs Telephone connections

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

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

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

Switches and Bridges Repeater Bridge

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

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

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

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

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

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

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

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.

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

MAU Multistation Access Unit `` Ring inRing out Computer Ports

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

Link Layer The End REMEMBER TEST NEXT WEEK!