Networking Refresher

A mini networking refresher! This was done by me for my CEH Theory test :)

Networking Refresher

Networking is the exchange of information and ideas among people with a common profession or special interest, usually in an informal social setting. I recently felt like I had trouble remembering some of the stuff related to networking. Thus, I decided to take a small refresher and write stuff down so that they would stick with me better! What better way than to blog about it? 😏


IP Addressing (Layer 3)

IPV4

  • Decimal notation
  • 32 bits

IPV6

  • Hexadecimal notation
  • 128 bits

Network Address Translation (NAT)

  • Network address translation is a method of remapping one IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device.

Classful Network

A classful network is a network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing in 1993. The method divides the IP address space for Internet Protocol version 4 into five address classes based on the leading four address bits.

Private / Public IP Address classes

MAC Addresses (Layer 2)

A media access control address is a unique identifier assigned to a network interface controller for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth.

  • Related to switching
  • 48 bits
  • Contains 6 pairs of twos [00:0c:29:78:a2:a2]
  • First 3 pairs/half = Identifier [Able to identify the vendor of the NIC]

TCP, UDP and the Three-Way Handshake

TCP (Transmission Control Protocol) is a standard that defines how to establish and maintain a network conversation through which application programs can exchange data. [Connection oriented protocol]

UDP (User Datagram Protocol) is an alternative communications protocol to Transmission Control Protocol (TCP) used primarily for establishing low-latency and loss-tolerating connections between applications on the internet. [Connection-less protocol]

A three-way handshake is a method used in a TCP/IP network to create a connection between a local host/client and server

TCP

  • Connection-Oriented Protocol
  • High Reliability
  • HTTP
  • HTTP
  • FTP
  • SSH

How does the TCP Three-way handshake work?

To Initiate a connection:

SYN → SYN, ACK → ACK

To gracefully terminate a connection:

FIN → FIN, ACK → ACK

UDP

  • Connection-less Protocol
  • Less Reliable
  • Streaming
  • DNS
  • VOIP

Common Ports and Protocols

  • TCP (Transmission Control Protocol)
  • FTP | 21
  • SSH | 22
  • Telnet | 23
  • SMTP | 25
  • DNS | 53
  • HTTP | 80
  • HTTPS | 443
  • POP3 | 110
  • SMB | 139 + 445
  • IMAP | 143
  • UDP (User Diagram Protocol)
  • DNS | 53
  • DHCP | 67 . 68
  • TFTP | 69
  • SNMP | 161

The OSI Model

The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology.

1 | Physical → data cables, Cat6

2 | Data link → Switching, MAC Addresses

3 | Network → IP Addresses, Routing

4 | Transport → TCP, UDP

5 | Session → Session Management

5 | Presentation → WMV, JPEG, MOV

6 | Application → HTTP, SMTP