Kran-Tobal prison was a prison on Bajor during and after the Cardassian Occupation.
After Ibudan had been arrested for murdering a Cardassian officer, he was sent here where he usually was around with Bajoran dissidents. One of them taught Ibudan his methods of tri-phasic cloning, which Ibudan used after his release in 2369 to create a clone of himself and let Odo appear as that clone's murderer.
Quark had some friends at Kran-Tobal, which he asked about Ibudan's time there trying to help Odo. (DS9: "A Man Alone")
When Major Kira kidnapped Surmak Ren to force him develop an antidote to the aphasia virus the same year, he threatened she'd spend the rest of her life in Kran-Tobal prison, if she didn't bring him back immediately. (DS9: "Babel")