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Networking Fundamentals · Foundational

ICMP Echo Request

ICMP type 8 message sent by ping to test whether a destination is reachable.

Definition

The destination responds with an Echo Reply containing the same identifier, sequence number and data. Many hosts and firewalls block echo requests, so a lack of reply does not always mean the host is down. ICMPv6 uses type 128.

Example

ping 10.0.0.1 sends a series of ICMP type 8 messages.

Exam tip

Echo Request is type 8; Echo Reply is type 0.

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