IP

Message Structure

• Version: 4 (IPv4) and 6 (IPv6).
• Differentiate services: To obtain better services, not generally used.
• Total length: Including the head length and the length of the data part.
• Survival time: Prevent undelivered(无法交付) data from constantly circled on the Internet.
• Protocol: Indicates which protocol the carrying data should be handed over for processing, such as ICMP, TCP, UDP, etc.

Special IP Address

• 0.0.0.0：All unclear host and destination networks.
• 255.255.255.255： Restrict broadcast address. Refers to all hosts in the same broadcast domain and cannot be forwarded by the router.
• 127.0.0.1：The local address and cannot be sent to the network interface.