Introduction to Computer Networking AE6382

Transcription

1

2 Computer Networks

3 How do you transfer data between two computers??

4 Carry your data on a memory stick, floppy, or 9 track computer tape from one computer to the other. slow limited distance secure

5 A better solution is to send data over a wire. Use a direct connection between each computer. Point-to-point connection. fast convenient

6 Now add a third computer.

7 And a fourth computer. Introduction to Computer Networking

8 The problem is that this solution does not scale. A very large network would look like this.

9 An alternative form is a tree structure. E D F A B C G

10 A star structure is a more flexible alternative.

11 This arrangement forms the basis of modern computer networks. The center node directs traffic from a source computer to a destination computer. A virtual point-to-point connection is created. The center node is a switch in an Ethernet based network and a router in an IP based network.

12 The Internet today is a combination of both the star and tree structure. Local networks are configured as stars (ethernet) and these are interconnected in a tree (IP). Computers on the local ethernet network are connected by way of an ethernet switch. Each of these local networks are connected by way of routers. Each packet will travel from end to end of the virtual connection created between two nodes.

13 Protocols

14 Protocols are the rules that govern how data travels over the computer network. how data is packaged into discrete increments (packets/frames) what the packet components mean proper sequence of packet transmission and reply

15 Ethernet is a low level protocol. It is used to implement networks of closely located computers LAN or Local Area Network. Ethernet is transmitted in frames. An ethernet address is 48 bits long. 00:1a:a0:b3:42:79 each digit is hexadecimal, 0-f each ethernet adapter has a unique address, this is the MAC address

16 Two types of ethernet frames, IEEE is commonly used

17 IP is a higher level protocol. It is normally used on top of ethernet. It has the advantage of being able to operate over very large networks. It is the basis of the Internet. IP is transmitted in packets. An IP address is 32 bits in length each component ranges from there is a network and host part each address is unique the center node for IP is a router

18 An IP packet Introduction to Computer Networking

19 TCP is an even higher level protocol. It is used on top of IP. It is a connection oriented protocol with reliable delivery. TCP is transmitted in packets. An TCP address (port) is 16 bits in length each port addresses a service on a computer

20 A TCP packet Introduction to Computer Networking

21 The relationship between the 3 protocols just presented is as follows: The data you are sending is packaged into the data part of a TCP packet with the port address of the destination specified. The resulting TCP packet is then inserted into the data part of an IP packet. The IP address of the destination computer is specified here. Finally, the combined TCP/IP packet is inserted into the data section of an ethernet frame. The frame is transmitted to the computer with the specified destination MAC address. At the destination the reverse process is performed until the original data is presented to the receiving program.

22 The actual sequence is more complex. There are also even higher levels, application protocols, inserted inside of a TCP packet s data field. Example application protocols ssh 22 http 80 secure shell, encrypted communications web access https 443 encrypted web access rdp 3389 Windows remote desktop

23 Domain Name Service

24 Domain Name Service (DNS) refers to the mechanism used to map names with IP addresses. Examples asdl.ae.gatech.edu C:\>nslookup Server: gw-asdl00.asdl.ae.gatech.edu Address: Non-authoritative answer: Name: Addresses: , , , Aliases:

25 Reverse lookups can also be performed C:\>nslookup Server: gw-asdl00.asdl.ae.gatech.edu Address: Name: newweb.gatech.edu Address:

26 Some Basic Network Tools

27 Windows Network Commands ipconfig a command that will display configuration of all network devices (see ipconfig /help) ipconfig /all ipconfig /release and ipconfig /renew route a command that will configure and display the current route tables on your computer (see route help) route add mask this will setup a static route route print netstat a command to display current network connections (see netstat help) netstat default to display current TCP connections netstat a display all connections, including listening tracert this command will display the path to the target host tracert

28 Windows Network Commands ping send a ping packet to the remote host (some hosts do not respond) ping nbtstat display MS specific network info (see nbtstat help) nbtstat A asdlserver.asdl.ae.gatech.edu nslookup perform DNS name and IP number mapping lookups nslookup nslookup

29 Windows - ipconfig The ipconfig command will display the current IP configuration of a windows computer.

30 Windows - nbtstat The nbtstat command displays information about other Windows systems on the network. It accepts either DNS name or NetBIOS name.

31 Windows - netstat

32 Windows - netstat

33 Windows - netstat :

34 Windows - arp :

35 Windows - tracert :

36 Linux/Unix network commands ifconfig configure and display network devices ifconfig eth0 display configuration of eth0 route configure and display the hosts route tables route display route table ip multi-purpose network command ip addr display network configurations ip route display route table netstat display current network connections netstat display all current tcp and udp connections netstat at display all current tcp connections including listening ports

37 Linux/Unix network commands traceroute display the path to remote host traceroute ping send a ping to the remote host ping