[1] What is SMUX?

SMUX is the snmp multiplexing protocol (RFC 1227). It can be used by an
snmp agent to query variables maintained by another user-level process.

[2] Why is it relevant to net-snmp?

The original ucd-snmp agent needed a mechanism to query statistics from
GateD.  GateD has traditionally supported this functionality via SMUX.
Hence SMUX was implemented within the ucd-snmp framework to extract
routing protocol statistics from GateD.

net-snmp continues to support smux, and many applications still use it.

[3] What is GateD?

GateD is the 'Gateway Daemon' which implements a variety of routing
protocols on a variety of platforms (OSes). This was formerly available
as open source, but has since been made closed and entirely un-free.
Other routing protocol daemons such a quagga (http://www.quagga.net)
support SMUX.

[4] Can SMUX extract statistics from other user-level processes?

Yes, the current implementation allows for the registration of any MIB
that might be registered by a SMUX peer.

[5] How does it work?

Assuming 'snmpd' is already up and running, when the SMUX peer comes up,
it identifies itself with an oid identifier and string password, and
registers any MIBs it would like to implement.  When 'snmpd' receives
queries for these MIBs, it passes these queries to the peer.

[6] Who implemented SMUX for ucd-snmp?

SMUX was implemented by Rohit Dube. He had oodles of help from
ucd-snmp-coders (Dave, Niels, Wes, Simon, Felix, Leonti) and gated-people
(Acee, Feiyi, Larry, Sue). [If I missed somebody, sorry in advance and
do let me know].  Later, Nick Amato re-write the entire SMUX package so
the code today is mostly his.

[7] How do I find out more about SMUX?

Read the RFC and the code, mainly, but only for legacy code.

*New* sub-agent development should use the AgentX protocol instead,
which is not only standardized (RFC 2741 + 2742), but is outright superior
to smux in a number of important ways (handles SET requests reliably,
able to handle overlapping registrations, aware of SNMPv3 contexts, etc.)

Only build new smux support if you have to.