Network Layer – IP Protocol Layer 3

What is Network Layer ?

• Network layer is the Layer 3 of the OSI Model.
• Network Layer is the Layer where the IP Address Lives.
• IP (Internet Protocol) determines where we are going to send packets to by looking at the destination IP address.
• How we determine where to send them is up to the routing protocol,
• IP uses unit called as Packet, so we normally refer to as IP Packet.
• IP itself does not setup a connection, in order to transport data you need the “transport” layer and use TCP or UDP.

IP Address and It’s Characteristics

What is IP Address ?

IP address is just an identity for the deivice.

• 32-Bit Address
• Splits into 2 part as Network and Host
• 4 Octet
• 1 Octet = 8bit
• 4 Octet = 4 * 8 = 32 Bit
• Represented in Decimal format

Default Network and Host Format

By Default, 

• Class A network will have a 8-bit (1st Octet) as a Network part and the remaining 24-bit(2nd,3rd and 4th) as a host part.
• Class B network will have a 16-bit (1st and 2nd Octet) as a Network part and the remaining 16-bit(3rd and 4th Octet) as a host part.
• Class C network will have a 24-bit (1st,2nd and 3rd Octet) as a Network part and the remaining 8-bit(4th Octet) as a host part.

IPV4 Classes:

• Class A - 0.0.0.0    - 126.255.255.255
• Class B - 128.0.0.0 - 191.255.255.255
• Class C - 192.0.0.0 - 223.255.255.255
• Class D - 224.0.0.0 – 239.255.255.255
• Class E - 240.0.0.0 - 254.255.255.254

1. We are not using Class D & E IP Address range
2. Class D is only for Multicast 
3. Class E is under Research purpose

IPV4 Frame Format

          From the Above Frame format, Just look into the Red and Blue fields,

The mentioned Red and Blue Fields are the ones that are necessary and basics mandatory fields for an IP packet.

Protocol : This field gives the information about what type of Protocol used in Layer 4 (Transport layer). The Protocol may be TCP or UDP.

Source Address : This field gives the information about from which interface the packets are generating as a source to reach the destination. It may be any physical Interface, Loopback, Tunnel or any other Interface.

Destination Address : This field gives the information about the IP that is to be reached from this Router with the mentioned source.

Data : Information carried from the packet.

Default subnet Mask of IPv4 Address

• If you Look closer 127.0.0.0 segment will not be there.
• The reason for this is it will check for whether your internal IP stack is OK
• You can go to command prompt in your PC, and try to ping 127.0.0.1,  you will get a response.

Private and Public IP Address

    Private IP range

             Class A: 10.0.0.0 – 10.255.255.255

             Class B: 172.16.0.0 – 172.31.255.255

             Class C: 192.168.0.0 – 192.168.255.255

    Public IP range

•  IP address other than above mentioned range are said to be as Public IP address
•  Public IP addresses are used on the Internet.
•  Private IP addresses are used on your local area network and should not be used on the Internet.

APIPA 

•  APIPA - Automatic Private IP Addressing
•  If the PC unable to get an IP Address, Windows will automatically assign an IP to PC,     that IP range is said to be APIPA
• APIPA IP range : 169.254.0.0 to 169.254.255.255
• You can also look into my Video:
• That's all about Network Layer...