Significance of 7E8

I am new to the field of automotive electronics and am currently trying to understand the working of the CAN bus. I understand that when we connect a CAN bus logger to the OBD2 port in a car we will be able to view the CAN traffic (raw CAN frames) and in order to get specific information from ECUs, we can send a request with ID 7DF and would get a response with IDs between 7E8 to 7EF. Is 7E8 actually the ID of the responding ECU or is it a general-purpose address just to relay the response back to the sender. Further, why 7DF has been chosen to send a request? Is there a specific reason? I apologize if any of the above statements are not right. But I could not find any material on the internet providing this clarification. Any help is much appreciated. Thank you.