Counts outbound packets that could not be transmitted due to errors. A nonzero and climbing ifOutErrors on an otherwise healthy link usually points to a physical-layer problem, such as a duplex mismatch, a failing NIC, or a bad cable, rather than a software or policy issue, since the packet already made it through the firewall's own decision logic before failing to go out the wire. Example: ifOutErrors climbing on one interface while its link partner shows a duplex mismatch in its own counters confirms a cabling or negotiation issue rather than a routing problem.