Computer Networks Encryption CS100 PROFESSOR SULTANA GMU CS Dept Slides Adapted from Dr Zaman Lecture on Networking Categorizing Computer Networks based on Host Role Peer to Peer Networking Client Server Networking Categorizing Computer Networks based on Geography LAN Local Area Network or office building WAN Wide Area Network Network that connects computers and devices in a limited geographical area like a home school Connects networks over larger geographical areas such as cities countries or even globally Categorizing Computer Network based on type of Signaling used by the Network Baseband the entire bandwidth of the communication medium is used to send a single data signal Broadband allows multiple signals to be sent simultaneously over the same medium by dividing the bandwidth into multiple channels Peer to Peer Provide Consume Client Server Server Provides Client Consumes Hardware Network Interface Card NIC is a device with a unique 48 bit address that provides a way to link computers through the physical media This device is also known as a LAN adapter a network card or a network interface Network interface cards make a physical connection to the network which is used to send information locally on a LAN or to remote devices on the Internet Media used for Network Connections Wire Cabling coaxial Copper Twisted Pair Fiber Optic Cable Electromagnetic Interference Most to Least susceptible What are Internets made of Clips and cables and wireless signals that s what Internets are made of The Internet is a network with two major design principles in mind That it works over any type of network hardware That it is extremely fault tolerant The Internet is a global network Where did the Internet come from The Internet is much older than most people realize It originates from the ARPANET which dates back to 1969 Its development was pushed mainly by two groups academia and the military Universities wanted an efficient way to share information plus a way to interconnect arbitrary new network technologies The military wanted a communications tool which was hard to disrupt Backbone Example GTT The backbone of the Internet is made up of high volume global connections operated by the largest Internet providers These few providers are known as Tier 1 providers GTT Global Telecom and Technology is a Tier 1 provider based in Arlington VA Source GTT What about ordinary connections The Internet was designed to be usable over any network hardware Including wired Ethernet wireless telephone etc A note about routing An Internet connection typically isn t a cable going straight from your computer to the machine you re talking to Instead Internet packets go hop by hop from machine to machine network to network in order to reach their destination A message can cross a number of machines and several completely different type of networks before it gets where it wants to go Sometimes more than one path or route exists between two different machines If a route becomes unusable due to network failure or congestion a message can be rerouted Communication Layers How does the Internet achieve this flexibility It does so by splitting the task into several layers First no matter what kind of network it is it has to have some way to send messages to other network nodes Once we can do that we pack Internet messages known as packets into the physical network messages The Internet Protocol will split the full message into smaller packets to send them to their destination Once we can do that we can build reliability i e the ability to resend or reroute packets into the scheme streams Services i e email or web are built on top of reliable end to end communication First let s use ZEUS Zeus is a computing resource that s available to all students faculty on campus and off campus if using the VPN Most common server we will be using zeus cec gmu edu o ssh ing Secure Shell protocol to connect to a remote computer o Treat it like one drive something that can be accessed from anywhere vs Things locally stored on you device Internet Tools ping We can check whether another machine on the Internet is reachable and how long it takes to get there To do that we use a command called ping Usable from the terminal Mac or command prompt powershell Windows All you need is the command and the computer you re trying to reach C02S41E3FVH6 shvethas ping google com PING google com 172 217 9 206 56 data bytes 64 bytes from 172 217 9 206 icmp seq 0 ttl 57 time 6 526 ms 64 bytes from 172 217 9 206 icmp seq 1 ttl 57 time 4 829 ms 64 bytes from 172 217 9 206 icmp seq 2 ttl 57 time 3 872 ms 64 bytes from 172 217 9 206 icmp seq 3 ttl 57 time 6 125 ms 64 bytes from 172 217 9 206 icmp seq 4 ttl 57 time 6 450 ms 64 bytes from 172 217 9 206 icmp seq 5 ttl 57 time 3 739 ms 64 bytes from 172 217 9 206 icmp seq 6 ttl 57 time 5 951 ms C google com ping statistics 7 packets transmitted 7 packets received 0 0 packet loss round trip min avg max stddev 3 739 5 356 6 526 1 109 ms Note 172 217 9 206 is an IP address for Google Internet Tools traceroute We can use traceroute Mac or tracert Windows to find out the path our messages take to get to another machine C02S41E3FVH6 shvethas traceroute google com traceroute to google com 172 217 13 238 64 hops max 52 byte packets 1 g3100 192 168 1 1 1 916 ms 1 969 ms 1 926 ms 2 6 3 ae1304 21 artnvafc mse01 aa ie1 verizon gni net 100 41 23 26 28 133 ms ae1304 20 washdcdn mse01 aa ie1 verizon gni net 100 41 23 24 6 565 ms ae1304 21 artnvafc mse01 aa ie1 verizon gni net 100 41 23 26 9 689 ms 4 0 ae9 gw13 iad8 alter net 140 222 225 63 7 304 ms 0 ae10 gw13 iad8 alter net 140 222 225 219 5 661 ms 4 773 ms 5 72 14 218 232 72 14 218 232 4 834 ms 7 315 ms 5 472 ms 7 108 170 240 97 108 170 240 97 8 793 ms 209 85 143 230 209 85 143 230 8 958 ms 108 170 240 97 108 170 240 97 8 569 ms 8 108 170 240 98 108 170 240 98 9 368 ms 108 170 240 112 108 170 240 112 9 018 ms 108 170 246 2 108 170 246 2 6 645 ms 9 iad23s61 in f14 1e100 net 172 217 13 238 3 650 ms 108 170 235 157 108 170 235 157 7 325 ms iad23s61 in f14 1e100 net 172 217 13 238 6 767 ms Looking up Internet Addresses If we only know the numerical address of some machine do we have any way to find out what the machine is Or if we know the name of …