IP Protocol, Apr/6/2023

Today, I learend about the Internet Protocol. It is the introduction part for IP Protocol.

 

Before start the IP, we should know about the Network Layer.

 

Network layer

• Transport segment from sending to receiving host
• On sending side encapsulates segments into datagrams
• On receiving side, delivers segments to transport layer
• Network layer protocols in every host, router
• Router examines header fields in all IP datagrams passing through it

Here is the picture of the internet network layer.

 

Before getting into the transport layer section, our internet goes through the network layer.

 

So, what is "IP datagram format" 🤨?

In other words, we say the basic unit of information thorough the internet!

 

It would be easy to understand with this picture.

IP datagram format

• "ver" means the IP protocol version number
• "Head. Len" is the length of the header. It is represent by byte
• "type of service" refers the type of data
• "length" is the total datagram length (bytes)
• 16-bit indentifier, flags and fragment offset is for the gragmentation/reassembly
• "Time to live" is for the max number remaining hops
• "Upper layer" protocol is for delivering payload
• "Header Checksum" checks the whether error is in datagram

The IP header check sume is important. IP header cheksum is calculated at source for the first time.

It is attached to the packet as a field of Network layer header.

 

Each router:

1. Detach Network layer header.
2. Test the checksum.
3. 1. Discard the packet. 
   2. or Decrement TTL field of Network layer header by 1.
   3. Calculate the new checksum
   4. Replace the checksum in Network layer header
   5. Attach the new Network layer header to payloadIf an error is detected.

Checksum

This is the short explaination for the check sum. We compare the source, if same --> no error, but if is not same it occurs the error and drop the packet!