txdropped

txdropped is a network statistic that records the number of packets that were transmitted but dropped along the transmit path before they could be sent on the wire. It typically counts packets that the host software or the network device driver rejected or failed to enqueue for transmission, rather than packets that were successfully transmitted or that were dropped on reception.

Where it appears and what it means

- In many operating systems and drivers, txdropped is exposed as part of the device’s statistics, such as the NetDevice statistics in Linux (for example, tx_dropped counters reported by ethtool or through /sys/class/net).

- It is distinct from tx_errors (transmit-related errors) and from receive-side drops (rx_dropped). A nonzero txdropped value generally indicates resource constraints or queue management decisions in the transmit path rather than errors during actual transmission on the wire.

Common causes

- Transmit queue overflow or insufficient transmit queue length, causing the driver or hardware to drop packets.

- DMA or resource allocation failures in the driver.

- Hardware or driver bugs that discard packets before they are enqueued for transmission.

- Software-based queuing or traffic control (TC) decisions that drop packets when the transmit path is congested.

Interpretation and troubleshooting

- A rising or high txdropped count often signals congestion or misconfiguration: insufficient TX queue depth, CPU resource limitations, or driver/hardware issues.

- Troubleshooting steps include checking driver and firmware versions, reviewing dmesg for related messages, increasing transmit queue length or ring sizes, tuning NIC offloads if appropriate, and monitoring overall system load. Consulting per-drivers statistics via tools like ethtool -S can help pinpoint the source.

See also: rx_dropped, tx_errors, net_device_stats, ethtool.