Question: What is the minimum required size for the IP reassembly buffer in a GTPv1-U receiving endpoint, considering both tunnel headers and inner MTU size?
Option 1: Inner MTU size only
Option 2: Outer IP header size plus GTP header size
Option 3: Inner MTU size plus the combined size of outer IP header, outer UDP header, and GTP header (including any extension headers)
Option 4: Maximum Transmission Unit (MTU) of the underlying network interface
Explanation: To ensure proper reassembly of IP fragments received via GTPv1-U tunnels, the buffer must accommodate both the largest possible inner packet (inner MTU size) and the additional overhead from tunneling (outer IP header, outer UDP header, and the entirety of the GTP header, including any extensions). This comprehensive sizing ensures that the receiving endpoint can handle all incoming packets without fragmentation issues.