As you know, the basic SNMP protocol allows some manager (for example, a copy of HP Openview) to communicate with some agent (for example, a Cisco router ... or your Linux PC).
All well and good. But what happens if some host (like your Linux PC) happens to have multiple, independent SNMP agents, each with its own separate MIB? How can one daemon (snmpd) on one port (UDP/161) handle multiple different MIBs?
One answer is "smux" - a protocol, and an API ... that happens to use port 199.
Yes, you can configure it. But you're probably best off if you just leave it alone.
Hope that helps .. PSM