What does errno 106 (EQFULL) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: The network interface output queue is full, so the system cannot accept more outbound work at that queue.

Could be also:
Constant	Type	OS
ERROR_SEM_USER_LIMIT	Win32 error	Windows
EISCONN	errno	Linux
ELAST	errno	Mac
ECONNABORTED	errno	Windows
LPC_INITIALIZATION_FAILED	BugCheck Code	Windows

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EISCONN	ELAST

EQFULL

This is local transmit-side backpressure

EQFULL identifies a full interface output queue. It is not proof that the remote host is down or that a particular peer rejected the request. The pressure is local to the path that accepts work for transmission, and it can be transient or persistent depending on the interface, driver, traffic shaping, and consumer progress.

Queue pressure should be handled by bounded buffering and backpressure, not by multiplying producers or retrying immediately. Preserve the interface or route context, packet or request class, queue occupancy if available, and the time until the queue drains.

What to correlate

Network interface, route, traffic class, send rate, packet sizes, and concurrent producer count.
Driver counters and drops around the failure time, including any shaping or policy layer between the application and interface.
Whether the application can defer, coalesce, or discard low-priority work instead of queueing unboundedly.

References

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