PLIP Parallel Line Internet Protocol networking
PLIP carries IP traffic between two PCs over a standard parallel printer port using a special "null-printer" or LapLink crossover cable. It was a popular way to network two machines in the 1990s when Ethernet cards were expensive, and it relied on the IEEE 1284 parallel ports that were standard on PCs through the early 2000s.
recommendation
Worth keeping but documenting as legacy because, although parallel ports have essentially vanished from modern PCs and almost nobody uses PLIP for networking today, the code is not abandoned: a real transmit-path bug fix landed upstream in October 2024 and was backported to stable kernels. Parallel-port hardware is also still sold new for niche uses like LinuxCNC, so the underlying ports do persist. Annotating it as a legacy niche feature would set expectations without disrupting the handful of remaining users.
repository signals
sources
- lore.kernel.org
Upstream netdev saw a real PLIP functional fix in October 2024 ('fix break; causing plip to never transmit'), indicating the driver is not fully abandoned.
- docs.kernel.org
Kernel documentation still describes PLIP as IP over a parallel port using null-printer/LapLink-style cables, confirming the hardware/protocol niche the driver serves.
- cateee.net
LKDDb shows CONFIG_PLIP remains present through current kernel series, so the driver is still buildable upstream.
- en.wikipedia.org
Parallel ports were common on PCs through the 2000s but are now virtually non-existent on new computers, supporting an 'obsolete but legacy/niche' deployment assessment.
- linuxcnc.org
Parallel-port hardware is still used in niche modern deployments such as LinuxCNC, including onboard and PCI/PCIe parallel-port cards, supporting 'still sold new' but low-volume status.
codex reasoning notes (technical)
Lore evidence came from `lore_file_timeline` on `drivers/net/plip/plip.c`, which showed 2024 upstream and stable activity including the cited netdev patch and stable backports; an attempted broader lore removal search timed out, so there is no positive evidence here of an active removal series. Deployment evidence came from `web.search_query` results for kernel docs, LKDDb, parallel-port background, and LinuxCNC niche current use. Conclusion: PLIP is clearly legacy and likely near-zero in new networking deployments, but recent bug-fix traffic argues against deprecation/removal right now; keep it, but annotate as legacy/niche.