What is the effect of configuring tcp-mss-sender and tcp-mss-receiver?

The TCP Maximum Segment Size (MSS) defines the largest payload (the data part of a TCP segment) that a device can receive in a single segment. Configuring tcp-mss-sender and tcp-mss-receiver on a FortiGate interface or within an IPsec tunnel configuration allows the firewall to intercept and modify the MSS value in the TCP SYN and SYN-ACK packets. This is primarily used to prevent packet fragmentation over links with lower MTUs (like IPsec or VXLAN) by ensuring the sender produces segments that fit within the tunnel ' s available payload space once encapsulation headers are added.

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