Communication model deals with how the management
data is communicated between the agent and manager process. It
is concerned with the transport protocol, the application
protocol, and commands and responses between peers. The
Functional model addresses the network management applications
that reside upon the network management station (NMS). The OSI
network management model categorizes five areas of function,
sometimes referred to as the FCAPS model: - Fault
- Configuration
- Accounting
- Performance
- Security
This network
management model has gained broad acceptance by vendors as a
useful way of describing the requirements for any network
management system.
Content 6.2 Network Management
6.2.3 SNMP and CMIP standards To allow for
interoperability of management across many different network
platforms, network management standards are required so that
vendors can implement and adhere to these standards. Two main
standards have emerged: - Simple Network Management
Protocol – IETF community
- Common Management
Information Protocol – Telecommunications community
Simple Network Management Protocol (SNMP) actually refers
to a set of standards for network management, including a
protocol, a database structure specification, and a set of data
objects. SNMP was adopted as the standard for TCP/IP internets
in 1989 and became very popular. An upgrade, known as SNMP
version 2c (SNMPv2c) was adopted in 1993. SNMPv2c provides
support for centralized and distributed network management
strategies, and included improvements in the structure of
management information (SMI), protocol operations, management
architecture, and security. This was designed to run on OSI
based networks as well as TCP/IP based networks. Since then
SNMPv3 has been released. To solve the security shortcomings of
SNMPv1 and SNMPv2c, SNMPv3 provides secure access to MIBs by
authenticating and encrypting packets over the network. The
common management information protocol (CMIP) is an OSI network
management protocol that was created and standardized by the
ISO for the monitoring and control of heterogeneous networks.
Web Links CMIP http://www.cisco.com/en/US/tech/
tk472/tk473/ tk119/tech_protocol_ home.html
Content
6.2 Network Management 6.2.4 SNMP operation
Simple Network Management Protocol (SNMP) is an application
layer protocol designed to facilitate the exchange of
management information between network devices. By using SNMP
to access management information data, such as packets per
second sent on an interface or number of open TCP connections,
network administrators can more easily manage network
performance to find and solve network problems. Today, SNMP is
the most popular protocol for managing diverse commercial,
university, and research internetworks. Standardization
activity continues even as vendors develop and release
state-of-the-art SNMP-based management applications. SNMP is a
simple protocol, yet its feature set is sufficiently powerful
to handle the difficult problems involved with the management
of heterogeneous networks. The organizational model for SNMP
based network management includes four elements: -
Management station
- Management agent
-
Management information base
- Network management
protocol
The network management station (NMS) is
usually a standalone workstation, but it may be implemented
over several systems. It includes a collection of software
called the network management application (NMA). The NMA
includes a user interface to allow authorized network managers
to manage the network. It responds to user commands and issued
commands to management agents throughout the network. The
management agents are key network platforms and devices, other
hosts, routers, bridges and hubs, equipped with SNMP so that
they can be managed. They respond to requests for information
and requests for actions from the NMS, such as polling, and may
provide the NMS with important but unsolicited information,
such as traps. All the management information of a particular
agent is stored in the management information base on that
agent. An agent might keep track of the following: -
Number and state of its virtual circuits
- Number of
certain kinds of error messages received
- Number of
bytes and packets in and out of the device
- Maximum
output queue length, for routers and other internetworking
devices
- Broadcast messages sent and received
- Network interfaces going down and coming up
The
NMS performs a monitoring function by retrieving the values
from the MIB. The NMS can cause an action to take place at an
agent. The communication between the manager and the agent is
carried out by an application layer network management
protocol. SNMP uses User Datagram Protocol (UDP) and
communicates over ports 161 and 162. It is based on an exchange
of messages. There are three common message types: -
Get – Enables the management station to retrieve the
value of MIB objects from the agent.
- Set –
Enables the management station to set the value of MIB objects
at the agent.
- Trap – Enables the agent to
notify the management station of significant events.
This model is referred to as a two-tier model. However,
it assumes that all network elements are manageable by SNMP.
This is not always the case, as some devices have a proprietary
management interface. In these cases, a three-tiered model is
required. A network manager who wants to obtain information or
control this proprietary node communicates with a proxy agent.
The proxy agent then translates the manager’s SNMP request into
a form appropriate to the target system and uses whatever
proprietary management protocol is appropriate to communicate
with the target system. Responses from the target to the proxy
are translated into SNMP messages and communicated back to the
manager. Network management applications often offload some
network management functionality to a remote monitor (RMON)
probe. The RMON probe gathers management information locally,
and then the network manager periodically retrieves a summary
of this data. The NMS is an ordinary workstation, running a
typical operating system. It has a large amount of RAM, to hold
all the management applications running at the same time. The
manager runs a typical network protocol stack, such as TCP/IP.
The network management applications rely on the host operating
system, and on the communication architecture. Examples of
network management applications are Ciscoworks2000, HP
Openview, and SNMPv2c. As discussed before, the manager may be
a standalone, centralized workstation sending out queries to
all agents, no matter where they are located. In a distributed
network, a decentralized architecture is more appropriate, with
local NMS at each site. These distributed NMS can act in a
client-server architecture, in which one NMS acts as a master
server, and the others are clients. The clients send their data
to the master server for centralized storage. An alternative is
that all distributed NMSs have equal responsibility, each with
their own manager databases, so the management information is
distributed over the peer NMSs. Web Links SNMP and MIB
Basics http://www.adventnet.com/products/ cagent/help/ Preface/
intro_snmpmib.html
Content 6.2 Network Management
6.2.5 Structure of management information and MIBs A
management information base (MIB) is used to store the
structured information representing network elements and their
attributes. The structure itself is defined in a standard
called the structure of management information (SMI), which
defines the data types that can be used to store an object, how
those objects are named, and how they are encoded for
transmission over a network. MIBs are highly structured
depositories for information about a device. Many standard MIBs
exist, but more MIBs that are proprietary exist to uniquely
manage different vendor’s devices. The original SMI MIB was