echorequest

Echo request is a term used to describe a message sent to elicit an immediate reply for testing connectivity, latency, or function. In networking, the most common form is the ICMP Echo Request, defined in RFC 792, used by the ping utility. An ICMP Echo Request (type 8, code 0) is sent to a host, and a corresponding ICMP Echo Reply (type 0) is returned. The payload can carry arbitrary data, which is echoed back by the responder, enabling measurement of round‑trip time and packet integrity. In IPv6 networks, ICMPv6 uses Type 128 Echo Request and Type 129 Echo Reply for the same purpose. An identifier and a sequence number help match replies to requests and detect out‑of‑order messages.

In application-layer contexts, many services implement echo endpoints that simply return the received input. Such endpoints are used for testing, debugging, and health checks, often via HTTP/S GET or POST requests that reflect the request body or parameters.

Security and operational considerations include the fact that ICMP traffic is frequently treated as low-priority or blocked by firewalls, which can affect reachability tests. Echo requests can be abused for reflection attacks or flood campaigns, so networks may rate‑limit or disable them. Echo endpoints in software should be designed with input validation and access controls to prevent unintended data exposure.

See also: ICMP, ICMPv6, ping, echo service, health check endpoint.