Network protocols

• Networking protocols define the rules and conventions for communication across a network.
• Protocols define speed of transmission, error checking, async/sync etc.

Handshaking

• The protocols are established between sender and receiver before starting communication.
• This is done via a handshake.
• Data packets are exchanged between various routers.

TCP 3-way handshake

IP vs Mac address

• A Mac address is provided by the NIC manufacturer and cannot be changed, but can be spoofed.

• An IP address is typically assigned by a router, and allows for easier communication across the internet and within your local network.

• IP addresses are more commonly used in networking applications.

IPs

IPv4

• 32-bit IP addresses
• Around 4 billion possible IPs
• 8 bits form an octet. Each octet may represent any number between 0 to 255.
• 192.123.45.94

Reserved IP Ranges

A → 10.x.x.x /8 B → 172.16.0.1 - 172.31.255.255.255 / 16 C → 192.168.x.x /24

Link local 127.0.0.1

x.x.x.0 is a network address rather than a device address

Broadcast address x.x.x.255

IPv6

• 128-bit IP addresses
• fc00:bbbb:bbbb:bb01::34:4e8e

Classful Addressing

• Initially, a network consisted of different classes
• Each class has a different structure of addressing
• Consider a large organisation; it will require class A addressing. In a single network, 2^24 hosts can be used. In total, only 2^7 such organisations can be addressed.

Classless Addressing

• In classless addressing, an IP address has an 8-bit suffix that specifies the number of bits allocated for network ID.
• For example, if the 8-bit suffix represents the number 14 and the remaining 18 bits represent the host ID.
• For example, 172.45.9.3/14 is represented in binary as given.

Subnet masking

• A subnet mask is used to identify the two parts of an IP address.
• For example, a subnet mask 255.0.0.0 represents a network ID of 8 bits and a host ID of 24 bits. This is equivalent to a suffix /8 in classless addressing. (CIDR)
• When AND operation is performed between an IP address and its subnet mask, its network ID is obtained.

Public and private

Private

• These addresses need not be registered on the internet registry.
• Private addressing for internal networks saves unique IPv4 addresses that can be used for routers and web servers that connect to the internet daily.

Public

• Some public IP addresses are also identified using domin names.
• A DNS server translates the domain name to an IP address.

Static and Dynamic addressing

Static Addressing

• Static IP addresses are assigned by the network administrator. When the device is in use, this address remains unused.

Dynamic IP Addressing

• An IP addressing can be used when the device is not used.
• The protocol responsible for this is dynamic host control protocol (DHCP)

Dynamic Host Control Protocol (DHCP)

• DHCP also provides subnet masks and other automatic configuration details. This eliminates the problem of manual configuration.

• Takes care of frequent changes in an IP address

• Allocates private addresses within an internal network

• Broadcast to all DHCP servers requesting an IP

• A DHCP server offers an IP for a particular duration

• Broadcasts a message confirming the request for IP

• DHCP server that offered the IP address sends an acknowledgement and assigns the DHCP client the IP address.

Port Numbers

• A port number is a 16-bit number attached to the IP address that is used to identify a process or application on a computer
• Using this number, an application running in the client system is accessed.

I am familiar with ports, so some information has been omitted.

NAT—Network Address Translation

• A network address translator provides external access to a privately addressed network as shown in the figure.
• 1 public IP is shared between all private IPs.
• Adds a layer of security
• Private IP addresses are not available to external servers
• Router tracks requests and reassigns them to the appropriate host
• Port numbers are assigned with a specific time frame

Port Forwarding

• Port forwarding is an application of NAT where port mappings are explicitly defined, allowing you to talk to services behind non-standard ports.

TCP/IP

• TCP/IP is a suite of communication protocols used to interconnect network devices of different manufacturers on the internet.

• Source → Sender of the message

• Destination → Receiver of the message

• Packet sequence → The order of the message in which it should be reassembled

• Data → Contents of the message

• Error checking → Bits to make sure that the message has been received correctly

User Datagram Protocol (UDP)

• A protocol similar to TCP but operates at a faster rate
• UDP: message is sent in the form of chunks or called datagrams
• TCP: message is sent as segments
• Used for gaming and video calling over the internet

HTTP

CRUD

C → Create → POST R → Read → GET U → Update → PUT D → Delete → DELETE

Email Communications: SMTP, POP3, IMAP

SMTP

• Send emails

POP3

• Retrieve mail from server
• Delete mail from server

IMAP

• Retrieve message from server
• Leave mail on the remote server

SSH (Secure Shell Protocol)

• Remotely access a terminal on another computer through a text interface

• SSH is used by network administrators and developers

• Typically runs on port 22

FTP (File Transfer Protocol)

• FTP defines the set of rules for transferring large files on the Internet
• The files required for a website are organised on a web server using this protocol.
• Users may have private access to upload the files. Other users may be given access to download these files.

VoIP (Voice over Internet Protocol)

• A set of protocols that enable you to make voice calls over the internet using UDP.

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