iOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPhone 6, released on 2017-12-13T18:13:17Z. The update package is 310.75 MB. This is a delta (partial) update that requires 11.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3bd5ff1803f7052222654ab3ae3bb52f2434b232.zip.