Computer network infrastructure: ARP protocol --- IP protocol --- ICMP + IGMP protocol

• ARP protocol
  • ARP cache: ARP address mapping to each item stored in the cache are set lifetime. Where more than the survival time of the project is deleted from the cache.
  • ARP is to solve the problem of mapping IP address and hardware address of the host or router on the same LAN.
    
• IP protocol
  • Using the IP protocol allows these diverse network performance from the user appears to be a unified network.
    
• ICMP protocol
  • In order to improve the delivery of IP datagrams chances of success in the Internet layer of the Internet Control Message Protocol ICMP.
  • ICMP allows the host or router report errors and provide reports on the situation abnormal situation.
  • ICMP packet format
    
• ICMP application protocol
  • PING
    • PING is used to test communication between two hosts.
    • PING uses ICMP echo request and echo-reply messages.
    • PING is ICMP network layer used as an example application layer protocol, it is not transported by TCP or UDP protocol layer.
  • Traceroute
    • Traceroute packet trace a path from the source point to the destination using the ICMP error reporting message over time.
    • principle:
      • Traceroute sends a series of IP datagrams from the source host to the destination host, encapsulated datagram is undeliverable UDP user datagram.
      • P1 is the first datagram TTL = 1, when P1 reaches the first router on the path R1, the router R1 to accept it, then the TTL - 1 = 0, R1 P1 is discarded, and sends an ICMP source host more than error report message.
      • Then the source host sends the second data packet P2, and TTL = 2. P2 to reach R1, R1 accept it and the TTL - 1 = 1, then forwarded to router R2, R2 and to accept TTL - 1 = 0, R2 P2 is discarded, and the source host sends an ICMP error reporting message longer than Wen. This has been continued.
      • When the last data packet just arrived at the destination host, the datagram TTL = 1. The host does not forward the datagram, the TTL is not decremented. But the IP datagram encapsulated in the transport layer is unable to complete delivery of UDP user datagram, so the destination host To send ICMP source end host unreachable error report message.
      • In this way, the source host will know the IP address of the router to reach the destination host elapsed, and wherein the round-trip time for each router to reach.