Glossary
What is ICMP?
A protocol used for network error messages and diagnostics such as ping.
IP networks use control messages to report connectivity conditions and delivery problems. Ping uses Echo messages, while traceroute can use responses such as time exceeded along the path. Related functions on IPv6 use ICMPv6. These messages do not check page content or an HTTP response.
Example
An Echo reply to an Echo request is the basis of a ping measurement. A time exceeded message from a network device can help inspect a route.
Common issue
Blocking ICMP can reduce diagnostic visibility without blocking every application connection. Evaluate web access with a separate HTTP or HTTPS check.