What’s happening here is our PC is sending a Type 8, Code 0 message which is an Echo Request to 10.44.44.4. We can confirm this with a Wireshark capture, looking at the response packet. If we check the ICMP Control Messages table, we can see Destination host unreachable maps to Type: 3, Code: 1. Packets: Sent = 4, Received = 4, Lost = 0 (0% loss) Reply from 10.250.1.1: Destination host unreachable. Pinging 10.44.44.4 with 32 bytes of data:
If I ping an IP on a network I know my router doesn’t have a route for, we get a Destination host unreachable message from the router ( Reply from 10.250.1.1). You’ve no doubt seen these messages when doing pings. A complete list of ICMP Types can be found on Wikipedia. For example, the Destination Unreachable type contains multiple Codes, one of which is 1, which maps to the message Destination host unreachable. ICMP is a diagnostic protocol and has a number of different message types, each one responsible for communicating a specific event - be it a ping request (called an Echo Request), a ping reply (called an Echo Reply), or a number of other diagnostic results.Įach message type consists of two fields, a Type field, which is a general grouping of similar sub-types, called Codes. Ping however uses a protocol called ICMP. Most traffic on the internet is encapsulated in either TCP, or UDP. ICMP and Ping ICMP (Internet Control Message Protocol) I’m not going to cover every detail, but a few key topics that have helped me troubleshoot and better understand issues over the years. So if you’ve ever used ping or traceroute, and wanted to know a little more, read on. I’ve found that having a good networking foundation has been a tremendous help in my day to day work. I wanted to write a post and do a bit of a deepdive into ICMP, ping and traceroute. ICMP, Ping, and Traceroute - What I Wish I Was Taught
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