IP header and IP address
IP protocol header
1. Version is the version of ip protocol, and it is now ipv4.
2. Header Length is the length of the head, accounting for 4 digits, with a maximum of 1111 (15), so the longest length of the head is 15*32bit=180bit (60Byte).
3. TOS is the service type field, the first 3bit is the priority, and the next 4 bits represent the service type, which are minimum delay, maximum throughput, maximum reliability and minimum cost, respectively, and the last bit is 0 unused.
4. The total length of Total Length is 16 bits, so the maximum total length is 65535Byte.
5. Identification shard identification, which is used for shard reassembly. The identity of the same packet is the same.
6. Flags logo to determine whether there are any subsequent shards, whether slicing is needed, etc.
7. Fragment Offset offset. If the first shard is 01460 of the data, then the offset of the first shard is 0, and the second is 1460.
8. TTL life cycle, which is used to prevent routing loops. Each time the data passes through a router, the value is minus 1, and the maximum value is 255. When the value is 0, the data will be discarded.
9. Protocol protocol number, indicating the upper layer protocol, for example, tcp is 6. Tudp is 17.
10. Header Checksum first checksum, data transmission checksum
11. Source IP source ip address
12. Destination IP destination ip address
13. Options option, there may be no option. The first 12 items share 20Byte. If there is no option, the IP header is 20Byte; if there is, then greater than 20Byte is less than or equal to 60Byte.
IP address
1. The IP address is 3 bits, which is generally expressed in dotted decimal system. The IP address is divided into network bits and host bits. The network bits of the IP address of the same network segment are the same. Each IP address has its subnet mask, with all the network bits of the subnet mask 1 and the host bits all 0. For example, the subnet mask for the address 192.168.1.1 Universe 24 is both 1 for the first 24 and 0 for the last 8 bits.
2. The last IP address of each subnet is the broadcast address, and the first is the subnet address.
3. IP addresses are divided into A, B, C, D and E addresses. The first three are used for normal network communication, class D addresses are multicast addresses, and class E addresses are used for scientific research.
4. Private address field
10.0.0.0 10.255.255.255
172.16.0.05172.31.255.255
192.168.0.05192.168.255.255
5. Special address
127.0.0.00127.255.255.255 loopback address
0.0.0.0 indicates all addresses
255.255.255.255 broadcast address (for broadcasting to all devices in the network)
6. Defects of IP addresses in the initial planning period: insufficient IPv4 addresses, resulting in subnetting; disordered entries in the road, and address summarization.
Important agreement
