The TCP MSS Adjustment feature enables the configuration of the maximum segment size (MSS) for transient packets that traverse a router, specifically TCP segments in the SYN bit set, when PPP over Ethernet (PPPoE) is being used in the network.
PPPoE truncates the Ethernet maximum transmission unit (MTU) 1492, and if the effective MTU on the hosts (PCs) is not changed, the router in between the host and the server can terminate the TCP sessions.
The ip tcp adjust-mss command specifies the MSS value on the intermediate router of the SYN packets to avoid truncation
Adjusts the MSS value of TCP SYN packets going through a router.
The max-segment-size argument is the maximum segment size, in bytes.
The range is from 500 to 1460.