ICMP RIP OSPF

(i) ICMP

IP is an unreliable protocol, and IP does not provide error control (if the data is in error during propagation), this time ICMP is working.

ICMP provides two functions: Error reporting, querying.

ICMP ICMP packets are divided into two categories, one is error message, and the other is query message.

ICMP target unreachable: That is, there is no way to send IP packets to the corresponding destination address, then the router will send an ICMP to the source host, tell him why the target is unreachable.

ICMP source suppression: When the host sends data to another host, the router issues an ICMP source suppress message if the speed reaches the saturation of the router or link.

ICMP Redirect message: If the router discovers that the sending host uses suboptimal paths to send data, then the router sends an ICMP to the host, saying there is a better path, which contains the most appropriate routing information and source data.

ICMP Timeout Message: There is a field TTL (Time to Live, lifetime) in the IP packet, and its value is reduced by 1 per router, until it is reduced to 0 o'clock that IP packet is discarded. At this point, the IP router sends an ICMP time-out message to the sending host and notifies the packet that it has been discarded.

ICMP echo Message: A message between the host or route used for communication to determine whether the sending packet successfully reached the peer. You can send an echo request message to the peer host, or you can receive a loopback reply message back to the end host.

Ping program

The ping program mainly uses the ICMP echo request message and the ECHO response message to test whether the target host can be reached. It is a basic diagnostic tool for checking system connectivity.

The ICMP echo request and the ICMP Echo reply message are working together. When the source host sends an ICMP echo request packet to the target host, it expects the response from the target host. After the target host receives an ICMP echo request packet, it exchanges the address of the source, destination host, and then sends the data portion of the received ICMP Echo Request packet intact in its own ICMP echo reply packet, then back to the party that sent the ICMP echo request. If the checksum is correct, the sender will assume that the target host's echo service is normal, that is, the physical connection is unblocked.

ICMP RIP OSPF