Network_Packet Structure

How am I connected to Google?

 

Method: Enter tracert 8.8.8.8 in the command prompt.

- tracert is a command used to trace the route to a DNS IP address.

- 8.8.8.8 is the IP address of Google's DNS server.

google DNS IP

- The result of the above command represents the network hops between

  Google and my computer through which data is transmitted.

 

- A total of 10 network hops were traversed for the data to be delivered to me

  from the Google DNS server.

 

- If an IP address is not visible, it means the connection has passed

  through a secure LAN segment.

 

 

Network Models: TCP/IP and OSI 7 Layers

 

Commonality:

- Both are models that define network functions in a hierarchical manner.

 

Differences:

- The number of layers differs: OSI is based on roles,

  while TCP/IP is based on protocols.

 

- OSI divides communication functions in detail,

  whereas TCP/IP is specialized in data transmission technology.

 

 

What is a packet?

- A packet is a term used to describe

  a formatted block of data transmitted over a network.

 

- Packets are structured in a way that specifies

  what data is being requested and from where.

 

- A packet is made up of a combination of various protocols.

 

- The payload refers to the actual data being sent.

 

- A footer is sometimes attached after the payload,

  but generally, footers are not used.

 

 

OSI protocal

- Before learning about encapsulation,

  it's important to know which OSI layer various protocols belong to.

 

 

 

Encapsulation Process

1. The HTTP protocol is used as the payload,

    and a TCP header is added to form a packet as shown above picture.

 

2. Then, both TCP and HTTP are used as the payload,

    and an IPv4 header is attached.

 

3. Finally, the IPv4, TCP, and HTTP are used as the payload, 

    and an Ethernet header is added.

    This is illustrated in the example diagram above picture.

 

- When sending data to someone, the payload encapsulation is

  carried out through a process similar to the above example.

 

- When adding headers, they are attached in the order of the OSI layers,

   from the upper or same layer down to the lower layer.

 

 

 

Decapsulation Process

- Decapsulation is the reverse process used to inspect the received data.

 

- A packet with a header from layer 4 protocols is called a segment.

 

- A packet with a header from layer 3 protocols is simply called a packet.

  (Note: Although the term "packet" is used,

   it has different meanings at different layers.)

 

- A packet with a header from layer 2 protocols is called a frame.

 

 

Packet example 1

 

- The picture above shows an ARP packet at layer 3, and in the case of Ethernet,

   it may have a special footer like 00 00 00 ... appended to the end. 

 

 

 

Packet example 2

- The picture above shows a packet composed of

  'Ethernet - ARP - footer' with no data.