RFC 1592 (rfc1592) - Page 3 of 54
Simple Network Management Protocol Distributed Protocol Interface Version 2
Alternative Format: Original Text Document
RFC 1592 SNMP-DPI March 1994
since 1989 and is included in the SNMP agents for VM, MVS and OS/2.
Version 1.2 of this protocol has been in use within BNR since 1992.
1.1 MOTIVATION
The Simple Network Management Protocol [1] defines a protocol that
permits operations on a collection of variables. This set of
variables is called the Management Information Base (MIB) and a core
set of variables has previously been defined [4, 5]; however, the
design of the MIB makes provision for extension of this core set.
Thus, an enterprise or individual can define variables of their own
which represent information of use to them. An example of a
potentially interesting variable which is not in the core MIB would
be CPU utilization (percent busy). Unfortunately, conventional SNMP
agent implementations provide no means for an end-user to make
available new variables.
Besides this, today there are many MIBs that people want to implement
on a system. Without a capability for sub-agents, this requires all
the MIBs to be implemented in one big monolithic agent, which is in
many cases undesirable.
The SNMP DPI addresses these issues by providing a light-weight
mechanism by which a process can register the existence of a MIB
variable or a MIB sub-tree with the SNMP agent. Requests for the
variable(s) that are received by the SNMP agent are passed to the
process acting as a sub-agent. The sub-agent then returns an
appropriate answer to the SNMP agent. The SNMP agent eventually
packages an SNMP response packet and sends the answer back to the
remote network management station that initiated the request.
Remote network management stations have no knowledge that the SNMP
agent calls on other processes to obtain an answer. As far as they
can tell, there is only one network management application (agent)
running on the host.
At the San Diego IETF (March 1992) a BOF was held on multiplexing
SNMP agent's requirements. Both the SMUX [6] and DPI [7] protocols
were discussed, as well as other unpublished approaches. There was
also discussion regarding a need for a standard for multiplexing SNMP
agents or sub-agent support. At the end of the BOF, however, there
was not enough support for defining a standard. This was due, at
least partially, to a few well known SNMP authors who stated that the
proxy and party support for SNMPv2 (SMP at the time) would solve the
problem.
Wijnen, Carpenter, Curran, Sehgal & Waters