Networking : How Internet Works
1. Browser is a web applications
2. Browser is communicate web server
3. Mobile applications are also web application with predefined URL and Webservers
4. URL is Uniform Resource Locator web address in simple term
5. Machine address is IP Address Internet Protocol Address (internet address)
6. Communication on internet happens between two applications using same type of
address means it is a combination of two IP addresses is talk to each other.
7. It is numerical value assigned to device participating in a network
8. It is used to identify devices on the network
9. IP Address can be assigned to a device by configuring another application on its
operating system
10. Physical address MAC address is a device address
11. All applications communicate with each other using IP address
12. When application communicate they send & receive both
13. Type "ipconfig" in command Prompt in windows OS & on linux OS "ifconfig" in the shell
14. Ping url on command prompt their are config ip address of any website
15. Ping our machine ip address for respond if alive.
Networking : Network & IP Addressing
1. Go to CMD with administration & type nslookup then type url & get url address
2. Open any browser & go to the nslookup.io & then search any url then get site address
3. Gateway Maintains a Table for each interface
4. Importance of having ports
5. Ip address have Ports know as TCP Ports Gateway does Network Address & Port
Translation
6. Go to CMD with administration & type netstat then get how many open ports of TCP like
local & foreign address & state
Networking : Protocols
1. TCP/IP Addressing
2. Each computer in a TCP/IP network must be given a unique identifier, or IP Address
3. This address operates at Layer 3
4. All comuters also have a unique physical address, known as a MAC Address or Media
Access Control Address. This are assigned by the manufacturer of the network interface
card.
5. This address operates at Layer 2
6. MAC Address is burned into ROM on a network interface card
7. MAC Address are 48 bits
8. MAC Address divide into 2 parts Vendor Code & Serial Number
9. Addresses type : Physical, IP, Port Address
10. TCP stands for Transmission Control Protocol
11. UDP stands for User Datagram Protocol
12. IP Address are 32 bits Addresses
13. Commonly expressed in decimal format e.g. (192.168.10.12)
14. Each "dotted decimal" is commonly called an octet (8bits)
15. IP Address Class Class A : net.host.host.host Class B : net.net.host.host Class C :
net.net.net.host
16. Subnet Mask : Assume: Address = 131.108.4.150 Network = 131.108 But we add
subnet mask also as Subnet Mask = 255.255.255.0 Subnet (or the effective network) =
131.108.4.0
Networking : Mapping & Scanning
1. Port Scanning: This techniques that attackers use to discover services they can break
into.
2. Idea : Sending a message to each port one at a time. Based on the type of response, an
attacker knows if the port is used. The used ports can be probed further for weakness.
3. Ports : All computers to connected to a LAN run various services that listen at some
ports. The use of port numbers are not unique. However, some port numbers become
standard for certain services. In general, port numbers are divided into two ranges.
4. Standard ports (0 - 1023) : Assigned to services by IANA (Internet Assigned Numbers
Authority). Only Super-user is allowed to open the ports.
5. Ex. ftp-data 20/udp, ftp21/tcp, ssh22/tcp
6. NMAP - Scanning tool :
7. Network exploration tool & security / port scanner
8. NMAP ("Network Mapper") is an open source tool for network explanation & security
auditing.
9. Designed to rapidly scan large networks.
10. NMAP is used to find hosts available on the network and what services (application
name & version) those hosts are offering, what OS & their versions they are running,
what type of packet filters/ firewalls are in use, & dozens of other characteristics.
11. NMAP characteristics: Flexible, Powerful, Portable, Easy, Free, Well Documented,
Supported, Acclaimed, Popular
Protocols & TCP/IP Handshake
1. Application A should established a formal connection with Application B.
2. What is Protocol?
3. In the previous Ex. For application A to communicate with application B & vice versa it
must follow certain rules. This set of rules are called protocols.
4. So, a Protocol is basically a set of rules that needs to followed by two devices or
applications to communicate over the network.
5. There are two types of protocols, they are TCP (Transition Control Protocol) - Reliable
Protocol UDP(User Datagram Protocol) – Unreliable Protocol
6. What is Sequence number & Acknowledgement number?
7. So to arrange those packets in particular order this is the Sequence & Acknowledgement
number.
