![]() ![]() ICMP Echo requests have code 0.Ĭhecksum: Used for error checking, calculation shown below. E.g.: 8 for ICMP Echo request, 0 for ICMP Echo reply.Ĭode: Additional codes for the type of message, full list. The general structure of a IMCP packet looks like this: In a previous chapter, the calculation of the IP header checksum is described. The “Total Length” is including the ICMP packet below, therefore changes made there must be met accordingly here. ![]() Important changes to the previous usage of the IP header in combination with TCP is the change of the “Protocol” to 01 for ICMP. We are going to reuse our IP header created in a previous chapter on IP headers and update it according to our needs: ICMP packets are encapsulated in IP packets. Looking at the sent and received ICMP packets in wireshark we can see the echo request and the corresponding reply: ![]() The screenshot shows one ICMP echo requests being sent to the host at 8.8.8.8 (Google DNS service). A typical output of the tool can be seen in the screenshot below: It works by sending a ICMP echo request packet to a target host and waiting for the ICMP echo reply. This kind of tool is typically available on all operating systems with networking capability. Ping is a tool to test the reachability of a host in a network. Many common network utilities like traceroute and ping are based on ICMP messages. The Internet Control Message Protocol (ICMP) is a network-layer protocol of the internet protocol suite (IP) used for sending error messages and diagnostic information indicating success or failure when communicating with another IP address. If you skipped the previous chapter you can find a short recap on the IP protocol header here. We are going to manually create ICMP packets to ping a target host. This chapter requires some knowledge about the internet protocol (IP) and it’s structure. ![]()
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