The Transmission Control Protocol (TCP) Maximum Segment Size (MSS) Adjustment feature enables the configuration of the maximum
segment size for transient packets that traverse a router, specifically TCP segments with the SYN bit set. Use the ip tcp adjust-mss command in interface configuration mode to specify the MSS value on the intermediate router of the SYN packets to avoid truncation.
When a host (usually a PC) initiates a TCP session with a server, it negotiates the IP segment size by using the MSS option
field in the TCP SYN packet. The value of the MSS field is determined by the MTU configuration on the host. The default MSS
value for a PC is 1500 bytes.
The ip tcp adjust-mss command helps prevent TCP sessions from being dropped by adjusting the MSS value of the TCP SYN packets.
The ip tcp adjust-mss command is effective only for TCP connections passing through the router.
In most cases, the optimum value for the max-segment-size argument of the ip tcp adjust-mss command is 1452 bytes.

Note
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TCP MSS adjustment-based traffic is always software switched.
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Supported Interfaces
TCP MSS Adjust is supported only on the following interfaces: