Which two GRE-related settings are configured to prevent packet fragmentation?

To prevent packet fragmentation with GRE tunnels, you configure IP MTU and TCP MSS. IP MTU (Maximum Transmission Unit) sets the largest packet size that can be transmitted without fragmentation at the IP layer. For GRE, this needs to account for the additional GRE header (typically 24 bytes) plus the outer IP header (typically 20 bytes). TCP MSS (Maximum Segment Size) is negotiated during the TCP handshake and specifies the largest segment of data that a TCP sender can transmit. By setting TCP MSS appropriately (e.g., subtracting 44 bytes from the interface MTU), you ensure that TCP segments fit within the GRE tunnel's effective MTU, preventing fragmentation. TCP window size and MTU ignore are not directly used to prevent fragmentation. The DF (Don't Fragment) bit, when set, prevents fragmentation but doesn't proactively adjust packet sizes.