IP protocol and IP address

---

1.IP agreement

The network layer is located between the data link layer and the transport layer . The network layer contains many protocols , The most important one is IP agreement . The network layer provides IP Routing functions , understand IP In addition to being familiar with routing IP Outside the working mechanism of the agreement , You must also understand IP Address and how to use it reasonably IP Address to design the network .

---

IP Baotou structure

• version
• Header Length
• Differentiated Services Filed
  • Differentiated Services Codepoint
  • Explicit Congestion Notification
• Identification
• Flags
• Fragment Offset
• Time to Live
• Protocol
• Header Checksum
• Source IP Address
• Destination IP Address
• IP Options
  

2.IP Field

Fragmentation

Fragmentation ： When packets are smaller than links MTU Big time , Can be broken down into many small enough fragments .

TTL：Time to Live, Time to live

• prevent IP Packets are transmitted endlessly in the network
• Every time you go through a route TTL The value will decrease 1
• When TTL=0 At the same time , Discard packets
  

Agreement No

• Used to identify the upper layer protocol
  

3.IP Address

• stay IP In the network , The communication node needs a IP Address
• Expressed in dotted decimal system , from 32 A composition
• It is divided into Network bit and Host bit Two parts ：
  • Network bit , representative IP The segment to which the address belongs
  • Host bit , Represents a node on a network segment
  • from Subnet mask Determine the dividing point
    

IP Address classification

According to the first set of octets