Improved Whip Proficiency (3.5e Feat)
From D&D Wiki
Improved Whip Proficiency [General]
Your whip attacks are less useless.
Prerequisite: Proficiency and weapon focus with a whip or similar weapon
Benefit: When wielding a whip or similar weapon, some of the normal limits are ignored. Your whip attacks deal lethal damage. Armor and natural armor does not negate damage from your whip attacks. You threaten the area within your reach. Using a whip does not provoke attacks of opportunity.
Normal: A whip deals nonlethal damage. It deals no damage to any creature with an armor bonus of +1 or higher or a natural armor bonus of +3 or higher. The whip is treated as a melee weapon with 15-foot reach, though you don’t threaten the area into which you can make an attack. Using a whip provokes an attack of opportunity, just as if you had used a ranged weapon.
Special: A fighter can select Improved Whip Proficiency as a fighter bonus feat.