Why is the packet fragmentation occurring between User-1 and Server-1 in this scenario?

Click the Exhibit button.

Referring to the exhibit, the GRE tunnel between R-1 and R-2 allows connectivity between User-1 and Server-1. When User-1 communicates with Server-2 with packets that are 1472 bytes in size, no packet fragmentation occurs. User-1 can communicate with Server-1 with packets that are up to 1448 bytes in size with no packet fragmentation. However, if the packet size is larger than 1448 bytes, packet fragmentation occurs.

Why is the packet fragmentation occurring between User-1 and Server-1 in this scenario?
A . The GRE header adds 20 bytes to the packet
B . The GRE header adds 24 bytes to the packet
C . The IP header adds 20 bytes to the packet
D . The IP header adds 24 bytes to the packet

Answer: B