I’ve been going through the World Book and I find it strange how during the first century and a half of living under Targaryen rule when Dorne was still an independent kingdom at that time, the Ironborn didn’t take the opportunity to go there for pillage and plunder. I can understand that after submitting to Targaryen rule the Ironborn stopped raiding lands that are under the protection of the Iron Throne as they would not stand a chance against the combined might of the Seven Kingdoms (as Balon Greyjoy would later learn).
However during the time Dorne was still a sovereign country it was outside of the Crown’s jurisdiction so it wasn’t off limits. Surely Dorne should have been the perfect hub for Ironborn raids during the years before it was finally integrated into the Seven Kingdoms. It is closer to home than the lands beyond Westeros and it’s very rich. Its coastal regions especially like Planky Town which brought in a lot of trade seem like ideal targets for eager Ironborn captains as there is plenty to plunder there and they could take their chances with the Martells as there would have been no interference from the Iron Throne.
Given how tenacious the Ironborn have proven themselves to be throughout history when it came to sating their desire to pillage and plunder and attacking pretty much anywhere that’s vulnerable (eg. The North), what was stopping them from conducting full scale raids in Dorne?
They probably did raid Dornish trade in the Narrow Sea, but the thing about Dorne’s southern coastline is that it’s really not good for sailing: “Nor is the long southern coast of Dorne more hospitable, being for the most part a snarl of reefs and rocks, with few protected anchorages. Those ships that do put ashore there, whether by choice or chance, find little to sustain them; there are no forests along the coast to provide timber for repairs, a scarcity of game, few farms, and fewer villages where provisions might be obtained. Even freshwater is hard to come by, and the seas south of Dorne are rife with whirlpools and infested with sharks and kraken.”
So the basic problem is that the Ironborn couldn’t really raid anywhere in between Skyfall and Plankytown because there aren’t really any coastal villages to raid. Also, the trip to Plankytown is a pain in the ass – if a storm blows up, you’re going to be wrecked and unable to repair your longboat or find food and water, and that’s assuming you don’t get eaten by sharks and krakens.
So my guess is that what the Ironborn would do instead is to run the gauntlet to the Narrow Sea and then prey on Dornish shipping there.