iOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPhone 6, released on 2017-12-13T18:13:08Z. The update package is 495.29 MB. This is a delta (partial) update that requires 11.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 4085dee8945b84d80531765a32ec0d66fea17e30.zip.