Icnd1 Notes

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A network
-Collection of devices that can talk to each other.
Applications that use the network
-Web browser and FTP
-Database application
-Instant messenger
-Email
-Online games
Considerations for network applications
-Speed
-bit byte (8 bits) kilobyte (1024 bytes) megabyte (1024 kilobytes) gigabyte (1024) terabyte (1024 gigabytes) -Delay
-Voip has certain delay requirements for voice to be transmitted into data from one point to the next -Availability
-How available is your network? Can it go down? If it goes down do you have a redundancy in place? Network designs
-Bus (used thin net)
-Star (switch in the middle, all devices connect to the switch) -Ring (token ring)
OSI Model
-Layer 1-4 are the only layers of the OSI model that are concerned in Cisco -Layer 5-7 are handled by the OS; Windows, Linux, etc.
-Application: interfaces with the application and provides network access to the application -Presentation: generifies the data (HTML) and encrypts services -Session: starts and ends sessions/logically keeps sessions separate -Transport: dictates how the data is sent and defines well known services (ports). (TCP/UDP) (source and dest port) -Network: provides logical addressing (IP address)/finds the best path to a destination (source ip and des t ip) -Data link: provides physical addressing (MAC) and ensures data is error free (source and dest MAC) -Physical: provides access to the cable/electrical signals that represent ones and zeros TCP/IP stack

-Application: Telnet, FTP, SMTP, DNS, RIP, SNMP
-Transport:TCP/UDP
-Internet: IP, ARP, IGMP, ICMP
-Network access: Ethernet, token ring, frame relay, ATM
IP address format
-4 numbers, each number 0-255
-Is always combined with a subnet mask and typically a default gateway -The subnet mask dictates which portions of the ip address identifies the network and host TCP
-Builds connections
-Uses sequence numbers (all packets have tags saying this is packet 1 and once it’s all received the computer grabs all the packets it received and assembles them in order) -Reliable (uses ACKS)
-Uses a three way handshake (SYNSYN-ACKACK)
UDP
-Connectionless
-Best-effort delivery
-unreliable
Ethernet
-CSMA/CD
-carrier: network signal
-sense: ability to detect
-multiple access: all devices have equal access
-collision: what happens if two devices send at once
-detection: how the computer handle collisions when they happen Types of communications methods in an Ethernet network
-unicast: one to one communication
-broadcast: sent to everyone except on the port it was received on -multicast: one message to a group;
Mac Address
-the first 6 characters (24 bits) are Organizational Unique Identifier -the next 6 characters (24 bits) are Vendor Assigned
Understanding Ethernet Cable
-Category 5 UTP
-max distance: 100 meters
-connection: RJ-45
-industry standard for Ethernet and most commonly used
-Multi-mode Fiber
-max distance: 275 meters to a few miles
-connection: varies (some proprietary)
-connectors are cheaper
-signal is dirtier than than single-mode
-Single-mode fiber
-max distance: 1 mile to many miles
-connection: varies (some proprietary)
-difficult to work with/usually requires a specialized technician Cabling standards
-because of the way the cable twists, ends should follow standards
-T568A + T568A = straight thru
-T568B+T568B = straight thru
-T568A+T568B= crossover
-unlike devices use straight thru
-like devices user crossover
The problem with CSMA/CD
-Hubs have 1 collision domain and 1 broadcast domain
-which means only 1 computer can send/receive at the same time
-all ports receive a broadcast
-JAM signal is sent out and each device stops sending signals and then restarts -Bridge was used to learn MAC addresses between hubs
-split the network into 2 collision domains
The problem with shared CSMA/CD
-Full-duplex communication
-each port is a collision domain
-mac address learning is now in ASIC...
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