In order to operate more efficiently, some applications such as Citrix and IIS combine many CIFS sessions into the same TCP connection. These connections are known as multiplexed connections. The 'cifs.max_mpx option' determines how many CIFS sessions can be multiplexed into a single TCP connection. When that value is reached, creation of new CIFS sessions within that TCP connection will fail and those users may not be able to access files via CIFS.
The value associated with the 'cifs.max_mpx option' should never be set below the Windows NT default of 50. If CIFS statistical output shows the Max Multiplex to be greater than 32, then this number should be raised. The only legal values are 50, 126, 253, 255* and 1124. Do not set this to any other values without an explicit conversation with NetApp customer service. It should be noted that automatically setting this option to a high value is not recommended. High values consume a lot of resources on the clients. Setting this to an unapproved value will cause errors on some clients.