Question: What is the purpose of the MME sending a SECURITY MODE COMMAND message with a new eKSI during a re-authentication procedure?
Option 1: To initiate a security mode control procedure using the current EPS security context.
Option 2: To create a new EPS security context and instruct the UE to use it for integrity protection and ciphering.
Option 3: To modify the current NAS security algorithms without changing the EPS security context.
Option 4: To request the UE to send a SECURITY MODE COMPLETE message without any security protection.
Explanation: The MME sends a SECURITY MODE COMMAND message with a new eKSI to create a new EPS security context and instruct the UE to use it for integrity protection and ciphering. This is done to ensure secure communication between the UE and the network after re-authentication.