Essentials of Computer Network
What is Computer Network?
A computer network is a system in which multiple computers are interconnected to each other to share information and resources.
Components of Network
1. Network Cables(Transmission Media)
2. NIC(Network Interface Card)
3. Hubs
4. Switches
5. Router
6. Servers
7. Client
OSI Model
Open System Interconnection Model(OSI) is a conceptual reference model to characterize and standardize the computer communication which happens over the computer network.
Layers of OSI Model:
1.Physical Layer: Media, signals and binary transmission between computer and network. Components: RS-232, RJ45, V34, SDH, DSL, 802.11
2.Data Link Layer: Physical addressing and node to node delivery of data in the form of frames. Components: Ethernet, 802.11,MAC, VALN,HDP,PPP.
3.Network Layer: Logical addressing and source to destination delivery in the form of packets. Protocols: IP, ARP, IPSec, ICMP, IGMP, OSPF.
4.Transport Layer: End to end connection and reliability in form of Segments or User Datagram. Protocols: TCP, UDP, SCTP, SSL, TLS.
5.Session Layer: Interhost Communication and Session Management in TCP,SIP,RIP.
6.Presentation Layer: Data Representation and encryption. This layer recognizes the data like: HTML, DOC, JPEJ, etc.
7. Application Layer: Network Processes to application. Protocols: DNS, WWW/HTTP, P2P, SMTP, etc.
TCP/IP Model
The real world application of OSI model is known as the TCP/IP model.
Attack On Various Layers:
1.Physical Layer: Eves dropping Attack, Jamming Attack
2.MAC layer: MAC Spoofing,MITM Attack(Man In The Middle)
3.Network Layer: IP Hijacking, IP Spoofing, Smurf Attack
4.Transport Layer: TCP Flood, UDP Flood
5.Application Layer: Malware Attack, SQL Injection, SMTP Attack
What is port number and what it does?
Port number is basically a way to identify specific process to which an internet or other network messages are to be forwarded to. It is a 16 bit number.
Types of Port [As decided by IANA]:
Well known Ports: 0–1023
Registered Ports: 1024–49151
Dynamic/Private Ports: 49152–65535
Few Important Port Numbers:
20–21: FTP
53: DNS
80:HTTP
110: POP3
3306:MySQL
8080:HTTP Proxy
443: HTTP over SSL[HTTPS]
Important Utilities and Tools to Understand Computer Network
Ping: This command is used to check connectivity
Ipconfig/ ifconfig: Shows the configuration of a specific network
Nestat: It shows the network statistics
Tracert/Tracepath: It shows the path between the client and server
NSLookup: Name Server Lookups
Arp: Map ip address to mac address
Pathping: Shows Detailed Ping Stats
Conclusion
As stated earlier this is just a brief introduction to a vast subject known as Computer Networking. I tried to cover as many important points as possible. If the topic interests you, there are many books available for computer networking for detailed study on the subject.