This read-create integer configures the TCP MSS (Maximum Segment Size) value to enforce on an IP interface built from this profile, ranging from 160 to 10240 bytes or 0 to disable the feature. When set, the router compares this configured value against the MSS advertised in TCP SYN packets crossing the interface and rewrites the packet to use whichever value is lower, a common technique for avoiding fragmentation over tunnels or reduced-MTU links. For example, setting juniIpProfileTcpMss to 1400 on a profile applied to a PPPoE interface clamps any TCP session's negotiated segment size down to 1400 bytes if the client requested something larger.