Extended Echo Request
ICMP Type 42 Extended Echo Request allows a host to query the operational status of a specific network interface by name, index, or address – without requiring layer-2 connectivity to that interface. Defined in RFC 8335, it extends the basic ping mechanism to probe individual interfaces on multi-homed or multi-interface devices.
Description
RFC 8335 defines Extended Echo Request and Reply (Types 42/43) to probe the operational status of specific network interfaces. Unlike basic ping which tests reachability to a host, Extended Echo identifies a specific interface by name (e.g., eth0), ifIndex, or IP address and reports whether that interface is operationally up or down.
This enables network operators to diagnose multi-interface devices where one interface may be down while the host is still reachable via another. The request includes an Interface Identification Object specifying how to identify the interface.
The reply (Type 43) carries state information: whether the interface exists, whether it is operationally active, and whether it is a point-to-point or broadcast interface. This is more actionable than a plain ping for diagnosing partial connectivity failures in complex network topologies.
Common Causes
- –Network management system querying interface operational state
- –Diagnosing partial connectivity on a multi-interface device
- –Verifying specific interface status without layer-2 adjacency