TCP/IP learning ---- IP datagram format

TCP/IP learning ---- IP datagram format the format of IP datagram is as follows (Here we only discuss IPv4) IP datagram format version 4B header length 4B service type (TOS) 8B total length (number of bytes) 16B flag 16 mark 3B offset 13B survival time (TTL) 8B protocol 8B header check and 16B source IP address 32B destination IP address 32B (note that the total length of the above fields is 20 bytes) option (if any) Data note: 1. The length of the IP datagram header and Data Length are both variable-length, but always an integer multiple of 4 bytes. for IPv4, the 4-bit version field is 4. 2. protocol fields refer to TCP, UDP, ICMP, and IGMP. 3. Only the IP header is verified, and the data validation is performed by a higher level protocol.