This reports the TCP Maximum Segment Size negotiated for this specific TCP connection underlying the FCIP link -- the largest chunk of data TCP will pack into a single segment. A smaller-than-expected MSS on this connection, often caused by an intermediate device or path MTU issue, means more per-segment overhead and worse throughput for the same amount of FC data being tunneled, which matters for diagnosing underperforming SAN extension links. An FCIP connection reporting an MSS of 536 bytes, a legacy minimum default, instead of a value closer to 1460 or more would indicate a path MTU discovery problem somewhere along the IP route, directly hurting FCIP throughput.