In IPV4, we can use this tcpdump command to filter all ICMP packets. Capture ICMP packets with Tcpdump Command
#Icmp checksum code
While this information alone might not be enough to troubleshoot a problem, if that packet were also to specify a Code field value of 3, indicating “port unreachable,” We could conclude that there is an issue with the port with which we are attempting to communicate. For example, a Type field value of 3 indicates “destination unreachable.” We might consider the ICMP Type field the packet’s classification and the Code field its subclass. That type of field is a one-byte field at the very beginning of the ICMP protocol header. If the type field is 8, then the packet is an ICMP echo (ping) request, while if the type field is 0, then the packet is an ICMP echo (ping) reply. The ICMP protocol has a field called type, which indicates what type the ICMP packet is. Variable A portion that varies depending on the Type and Code fields.Checksum Used to ensure that the contents of the ICMP header and data are intact upon arrival.Code The subclassification of the ICMP message, based on the RFC specification.Type The type or classification of the ICMP message, based on the RFC specification.
The ICMP header contains the following fields: ICMP contains a relatively small header that changes depending on its purpose. ICMP is part of IP, and it relies on IP to transmit its messages. Data is sent from one host to another as a request, and the receiving host should send that data back as a reply. The primary purpose of an ICMP ping is to test communication between devices. Most network-troubleshooting techniques and tools center around common ICMP message types. Internet Control Message Protocol (ICMP) is the utility protocol of TCP/IP, responsible for providing information regarding the availability of devices, services, or routes on a TCP/IP network. ICMP messages are encapsulated into IP datagrams, which are then encapsulated into an Ethernet frame. Internet Control Message Protocol (ICMP), described in RFC 792 and part of the TCP/IP protocol stack, is an error reporting and control-based protocol used between network devices.
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