I mean, we do have list of cameos on the cast list sections, but further context might be useful in case people has not seen other dramas that might be related to the cameos, for example:

  1. Director Kim Jung Shik brought a horde of casts from his other dramas as cameos such as So Not Worth It (Park Se Wan) and Strong Girl Nam Soon (Kim Jung Eun, Kim Hae Sook, Byeon Woo Seok, Kim Ki Doo, and Lee Joong Ok)
  2. Kim Jung Eun's cameo, in particular, also refers to her previous role in Lovers in Paris as it featured the drama's main ost in the BGM
  3.  Kim Sun Young (and Kim Chang Ho)'s cameo also refers to their character from Her Private Life. Both dramas share the same scriptwriter, Kim Hye Young

Those are just a few references that have been spotted, feel free to add more if you feel like we've missed something else! Also, since this drama has only aired 6 of the total 12 episodes, there might be more coming in the future.