Understanding the network.pdf - Back to Home

Protocol (SMGP) and the OSI Common Management Information Protocol (CMIP).
In 1988, the Internet Activities Board began an investigation to determine what
would be the Internet standard management model. SMGP, which was already in
use, had been passed over for the OSI's CMIP model. The problem was that, in the
CMIP IP version, CMIP over TCP (CMOT) was not ready for production deployment.
Therefore, for an interim period SMGP became the management standard. Then, a
transnational framework called SNMP was developed to provide a migration from
SMGP to CMOT. In 1990, SNMP was adopted as the standard management protocol
and management model for use on the Internet.
The SMMP management model uses managed devices, agents, and networkmanagement
systems. Managed devices are nodes running an SNMP agent. These
devices collect management data, then format and transmit using the SNMP
protocol. SNMP agents are processes that run on the managed device. The agent
maintains the local management's knowledge base of information for the device
they are operating on. The agent creates this local management knowledge base by
using the device's Management Information Base (MIB) as a collection template.
MIB is essentially a data map for collecting management information. The agent,
running on the managed device, collects management data using the MIB as a data
collection template. The network-management system sends and receives SNMP
messages to and from the managed devices. The agents then interpret the network
management station's data requests, which request certain MIB-defined data
objects, and return the requested data in SNMP form to the network management
station.
There are three versions of SNMP. The standard is SNMP v1, as defined in RFCs
1212, 1215, and 1213. SNMP v1 has the broadest support of all three versions. It
supports a community-based security model, which operates by having the devices
and the manager employ a common logical name for community identification,
authentication, and access, which can be either read-only or read and write. By
default, the community name "public" is used for read-only, and "private" is used
for read and write access. The community name is set by the network administrator.
It is also possible for a managed device to support more than one community name.
The community name is the only form of authentication for SNMP v1 to send and
receive SNMP messages. The community name must be common. If no name is set,
some clients will exchange SNMP messages with any network management station.
This open security model has some significant security implications. Additionally,
many administrators deploy devices without changing the default community
names, making it possible for anyone to send and receive SNMP information from
the device. As a rule, you should always change the default community names of
SNMP supportable network devices if you enable SNMP.
These security problems led to the development of SNMP v2 and SNMP v3. Both
versions are draft standards. SNMP v2 began as an enhanced version of SNMP v1
with additional security enhancements (authentication and access-control services)