What is ICMP Ping Packet

In computer network administration, a ping (Packet Internet or Inter-Network Groper) is a program that is used to determine if an IP address exists and can accept requests at a particular destination. To initiate a ping, we send an Internet Control Message Protocol (ICMP) Echo Request to a specified interface on the network and wait for a response.

Ping signals are sent to the specified address when the ping command is issued. In response to the echo request, the target host sends an echo reply packet. The ICMPv4 protocol, or ICMP, can be used to address network problems. The ICMP error and query messages not only alert the end systems during connectivity issues, but also provide diagnostic information from intermediary systems, such as the round-trip time. The ICMP protocol can be powerful, but it does not make IP reliable; it only provides error messages and messages related to data delivery. There is a possibility that the causes of delays in data transmission do not fall within the scope of the ICMP messages. When a transmission error occurs, TCP notifies the host. Aside from the Host Reachability (Echo Request/Echo Reply) messages, other ICMP messages include Destination Unreachable and Time Expiration. ICMP Echo Request and Echo Reply messages can be used to test an IP network’s reachability. The local host sends ICMP Echo Requests to the remote host. If the destination host is available, it responds with an Echo Reply. Ping uses ICMP Echo messages. An ICMP destination unreachable message is sent when a host or gateway is unable to deliver a packet. An error code is included in the message.

Here are some of the Destination Unreachable codes for ICMPv4: 0: Net unreachable, 1: Host unreachable, 2: Protocol unreachable, 3: Port unreachable.Routers use ICMPv4 Time Exceeded messages to indicate that a packet cannot be forwarded because the Time-to-Live (TTL) field has been decremented to 0. When the router receives an IPv4 packet with a TTL of zero, it throws the packet away and sends a Time Expired message to the source host. In general, ICMP messages can be categorized into two types: error reporting and queries. Every ICMP packet includes a Type, Code, and Checksum field. Query payloads differ from error messages, as each has a distinct purpose. Destination unreachable occurs when a router reports that the requested destination address is not reachable. If the hop limit reaches zero, time exceeded is sent. The problem associated with a parameter can occur when determining the field value in the header or extension header is problematic. The packet too large error occurs when a device is unable to transmit the data because the packet exceeds the Maximum Transmission Unit (MTU) of the outgoing link. The echo request/reply is used to confirm reachability. Routing solicitation/advertising is a means of soliciting and receiving information about routers, including their IP addresses.

Written by pramod