Layer - 3 Protocol (Router)

IP Addresses - There is two types of Ip addresses Inet is IPv4 (decimal) and inet6 is IPv6 (hexadecimal) we use these and communicate over Layer 3 Network. IPv4 is what we use everyday and is the most common.

all the numbers in the IP address bit wise adds up to 255.

With IPv4 we have 32 bits and we can have up-to 4billion IP spaces and mostly all of it is used. To solve that we have IPv6 which is 128bits which gives way way more possibilities(2^32) IPv6 mostly no one uses it.Even then we mostly always only IPv4 how do we still have space?

We are using NAT (Network Address Translation ) which assigns us private IP address so these addresses are only known to you.

We just rent the Public Address from our ISP and then divide it into private IP address.

Layer 2 (Physical Address)

MAC Address - Media Access Control .Its none as ether in ifconfig.Everything using a network will have MAC address and these are used to do switching .So this is their Physical Address .This how they communicate over Switches .The first three pairs of the mac address are Identifiers of the network and you can look it up on google and find where its running etc.

Layer 4 (Transport Layer)

TCP - Transmission Control Protocol(Suited for high reliability like making connections to websites,ftp,ssh)

UDP - User Datagram Protocol(Suited for more stuff like video streaming, Voice over IP, DNS so something that is connectionless)

Most common protocol we scan is TCP it works on Three way handshake

SYN > SYN ACK > ACK