Computer Network

  • A computer network is an interconnection of a group of computers.

Types of networks: 

  • Personal Area Network (PAN)
  • Local Area Network (LAN) 
  • Campus Area Network (CAN) 
  • Metropolitan Area Network (MAN)
  • Wide Area Network (WAN) 
  • Internetwork 
    • Intranet 

    • Extranet 

    • Internet

Network Hardware

  • Network Interface Cards 
  • Repeaters 
  • Hubs
  • Bridges 
  • Switches 
  • Routers 

Networking Concepts

Hostname

  • is the unique name by which a network-attached device (computer, file server, network storage device, fax machine, copier, cable modem, etc.) is known on a network. 

IP Address

  • is a unique address that certain electronic devices use in order to identify and communicate with each other on a computer network utilizing the Internet Protocol standard (IP)
  • IPv4 addressing Scheme  uses 32-bit (4 bytes) addresses, which limits the address space to 4,294,967,296 (232) possible unique addresses.

Port:

Protocol

  • a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints.

Packet

Network Model

The TCP/IP model is a layered abstract description for communications and computer network protocol design. (source: wikipedia)

Physical Layer:

  • Role: responsible for encoding and transmission of data over network communications media.
  • Ethernet physical layer · Modems · PLC · SONET/SDH · G.709 · Optical fiber · Coaxial cable · Twisted pair · 

Data Link Layer

  • Role: responsible for node to node (hop to hop) packet delivery.
  • 802.11 · 802.16 · Wi-Fi · WiMAX · ATM · DTM · Token ring · Ethernet · FDDI · Frame Relay · GPRS · EVDO · HSPA · HDLC · PPP · PPTP · L2TP · ISDN 

Network/Internet Layer

  • Role: responsible for end to end (source to destination) packet delivery,.
  • IP (IPv4 · IPv6) · OSPF · IS-IS · BGP · IPsec · ARP · RARP · RIP · ICMP · ICMPv6 ·

Transport Layer

  • Role: responsible for delivering data to the appropriate application process on the host computers
  • TCP · UDP · DCCP · SCTP · RTP · RSVP · IGMP ·

Application Layer

  • Role: interfaces directly to and performs common application services for the application processes;
  • DHCP · DNS · FTP · HTTP · IMAP4 · IRC · POP3 · SIP · SMTP · SNMP · SSH · TELNET · RPC ·

Some Important Protocols

IP (Internet Protocol)

  • a Network Layer Protocol
  • a data-oriented protocol used for communicating data across a packet-switched internetwork.
  • Provides Global scale hierarchical Address scheme? IP addressing and Routing

TCP (Transmission Control Protocol)

  • a Transport Layer Protocol
  • provides reliable, in-order delivery of a stream of bytes, making it suitable for applications like file transfer and e-mail
  • Protocol Operation:
    • connection establishment 

    • data transfer 

    • connection termination 

 

HTTP (Hypertext Transfer Protocol)

Port:

  • 80
  • 81 alternate

Utility:

  • Publishing and retrieving hypertext pages

Commands:

  • GET : to get the representation of a published resource
  • POST : to submit data to be processed

HTTP Status Codes:

  • 200: OK
  • 201: Accepted
  • 400: bad request
  • 401: Unauthorised
  • 403: Forbidden
  • 404: Not found
  • 500: Internal server error

 

FTP (File Transfer Protocol)

Concepts:

Commands:

  • GET : to get the representation of a published resource
  • POST : to submit data to be processed

Port:

  • 20 FTP data port
  • 21 FTP (control) Command Port

Utility:

  • File Sharing

Applications/Tools:

  • gftp
  • Bulletproof FTP

SSH (Secure Shell Remote Protocol)

Port:

  • 22 

Utility:

  • allows data to be exchanged over a secure channel between two computers 
  • typically used to log into a remote machine and execute commands

Applications/Tools:

  • openSSH
  • SSH Secure Shell 

 

POP3 (Post Office Protocol - Version 3)

Port:

  • 110

Utility:

  • Retrieving Email

Applications/Tools:

  • Outlook Express

 

SMTP (Simple Mail Transfer Protocol)

Port:

  • 25

Utility:

  • Email routing

Applications/Tools:

  • Outlook Express

 

Command line Tools Utilities

ipconfig/ifconfig

  • a command line interface that displays all current TCP/IP network configuration values
  • to display all active TCP connections and the TCP and UDP ports on which the computer is listening use ipconfig -all 

Netstat

  • a command-line tool that displays network connections, routing tables, and a number of network interface statistics.
  • to display all active TCP connections and the TCP and UDP ports on which the computer is listening use netstat  -a

Ping

  • a command-line tool that is used to test whether a particular host is reachable across an IP network.
  • using the known hostname: ping smtp.daiict.ac.in
  • using the known IP Address: ping 10.100.56.27

Tracert

  • traceroute is a computer network tool used to determine the route taken by packets across an IP network. 
  • using the known hostname: tracert smtp.daiict.ac.in

hostname

  • is the unique name by which a network-attached device (which could consist of a computer, file server, network storage device, fax machine, copier, cable modem, etc.) is known on a network.
  • to display the hostname of the system use hostname

 

Web Based Utilities

Visual Tracert

http://visualroute.visualware.com/

or

http://whatismyipaddress.com/staticpages/index.php/tools-visual-traceroute

Domain Dossier Investigate domains and IP addresses 

Function:

URL: http://centralops.net/co/DomainDossier.aspx

Example: 220.225.53.35

Email Dossier Investigate email addresses 

URL: http://centralops.net/asp/co/EmailDossier.vbs.asp

Browse Mirror

URL: http://centralops.net/asp/co/BrowserMirror.vbs.asp

Auto Who is

http://hexillion.com/asp/samples/AutoWhois.vbs.asp

ping

URL: http://centralops.net/asp/co/Ping.vbs.asp

Connection Test

URL: http://myvoipspeed.visualware.com/it/index.html

References:

 

Last modified: Wednesday, 10 July 2013, 3:09 PM