SNMP Monitoring: One Critical
Component to Network Management
Network Instruments White Paper
Although SNMP agents provide essential information for
effective network monitoring and troubleshooting, SNMP alone
does not provide all the information you need to stay on top of
your network. For comprehensive analysis of many issues, a
network analyzer with packet capture capabilities is required
as well. This white paper describes how SNMP works, the
advantages of SNMP monitoring, and how SNMP continues to
remain a critical part of a complete network analysis solution.
Overview
What is SNMP?
SNMP (Simple Network Management Protocol) is the common language of network monitoring–it is integrated into
most network infrastructure devices today, and many network management tools include the ability to pull and
receive SNMP information. SNMP extends network visibility into network-attached devices by providing data
collection services useful to any administrator. These devices include switches and routers as well as servers and
printers. The following information is designed to give the reader a general understanding of what SNMP is, the
benefits of SNMP, and the proper usage of SNMP as part of a complete network monitoring and management solution.
The Simple Network Management Protocol (SNMP) is a standard application layer protocol (defined by RFC 1157)
that allows a management station (the software that collects SNMP information) to poll agents running on network
devices for specific pieces of information. What the agents report is dependent on the device. For example, if the
agent is running on a server, it might report the server’s processor utilization and memory usage. If the agent is
running on a router, it could report statistics such as interface utilization, priority queue levels, congestion
notifications, environmental factors (i.e. fans are running, heat is acceptable), and interface status.
All SNMP-compliant devices include a specific text file called a Management Information Base (MIB). A MIB is a
collection of hierarchically organized information that defines what specific data can be collected from that
particular device. SNMP is the protocol used to access the information on the device the MIB describes. MIB
compilers convert these text-based MIB modules into a format usable by SNMP management stations. With this
information, the SNMP management station queries the device using different commands to obtain device-specific
information.
There are three principal commands that an SNMP management station uses to obtain information from an
SNMP agent:
1. The get command collects statistics on SNMP devices.
2. The set command changes the values of variables stored within the device.
3. The trap command reports on unusual events that occur on the SNMP device.
The SNMP management console reviews and analyzes the different variables maintained by that device to report
on device uptime, bandwidth utilization, and other network details.
SNMP delivers management information in a common, non-proprietary manner, making it easy for an administrator
to manage devices from different vendors using the same tools and interface. Its power is in the fact that it is a
standard: one SNMP-compliant management station can communicate with agents from multiple vendors, and do
so simultaneously. Illustration 1 shows a sample SNMP management station screen displaying key network statistics.
Another advantage of SNMP is in the type of data that can be acquired. For example, when using a protocol
analyzer to monitor network traffic from a switch's SPAN or mirror port, physical layer errors are invisible. This
is because switches do not forward error packets to either the original destination port or to the analysis port.
However, the switch maintains a count of the discarded error frames and this counter can be retrieved via an
SNMP query.
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Why use SNMP?
SNMP can be used in any environment where constant monitoring of key devices is required. Many SNMP
management stations offer long-term reporting capabilities, allowing an administrator to watch network trends
develop over time and to take appropriate action before problems can seriously affect users. Illustration 2
shows a sample report illustrating maximum, minimum and average router utilization.
Triggered notifications are also available from many SNMP management stations. Notifications allow the
administrator to receive an e-mail or page if certain user-defined thresholds have been exceeded, such as
maximum port utilization.
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Where should you use SNMP?
SNMP can be used in any environment where constant monitoring of key devices is required. Many SNMP
management stations offer long-term reporting capabilities, allowing an administrator to watch network trends
develop over time and to take appropriate action before problems can seriously affect users. Illustration 2
shows a sample report illustrating maximum, minimum and average router utilization.
Triggered notifications are also available from many SNMP management stations. Notifications allow the
administrator to receive an e-mail or page if certain user-defined thresholds have been exceeded, such as
maximum port utilization.www.networkinstruments.com
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What is missing from SNMP?
While SNMP provides excellent statistics on the macro level, it does not provide the level of detail that is often
required to completely resolve many network issues. For example, while SNMP may show high utilization on
the router’s Internet interface, it may not show what kinds of traffic are using up the bandwidth or who is
responsible for the traffic. This leaves the administrator knowing what the problem is (high bandwidth
consumption to the Internet), but not knowing the cause, and therefore, lacking the ability to quickly resolve
the issue. Illustration 3 shows how a network analyzer’s Top Talkers view with detailed analysis capabilities
can assist in in-depth problem solving scenarios. By reviewing the network’s Top Talkers (who is causing the
traffic), the network administrator can isolate the cause of the excessive utilization and take steps to
resolve the issue. This deeper level of detail is not found inside an SNMP management console. However a
network analyzer with SNMP management capability can offer the full view of the fundamental network issue.
Make no mistake-SNMP monitoring should be a part of any network management solution. But effective
administration of enterprise networks requires more than SNMP management. Only a comprehensive network
analyzer can deliver both in-depth analysis along with the ability to manage and view statistics from SNMPcompliant
devices. When selecting a network analyzer, choose a solution that provides full network coverage
for multi-vendor hardware networks including a console for SNMP devices anywhere on your LAN or WAN.
Also, look for a solution that includes a network mapping program that can help you visualize the network by
continually monitoring and displaying device and route statuses. In addition, the network analyzer should report
information about services running on the primary devices. This information is important to an administrator of
a single site, and invaluable to an administrator who is responsible for multiple sites. Often, the network
mapping program is integrated with the SNMP management station, allowing the two systems to share
information. This is accomplished by using the network mapping tool as a first step, SNMP as a high-level
drill down, and finally a network analyzer for deeper level statistics and information.
A comprehensive network analyzer also includes a packet decoding and analysis tool. Providing the additional
depth that SNMP management lacks, a network analyzer allows you to look beyond simple statistics into the
actual frames being transmitted across the network. While network analyzers vary greatly in their feature sets,
some of the primary functions you should look for in addition to packet capture and decode is some form of
Expert analysis for advanced problem identification and resolution, long-term reporting capabilities, and
triggered notifications. These features can provide ongoing insight into the day-to-day operations of the
network, at a level beyond the scope of SNMP. Figure 1 is a checklist designed for any network administrator
to review when choosing a comprehensive network management solution.
SNMP – A Component of Total Network Management
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Conclusion
SNMP management provides valuable insight to any network administrator who requires complete visibility
into the network, and it acts as a primary component of a complete management solution. However, SNMP
was never intended as a comprehensive network monitoring solution. It therefore must be complimented by a
complete suite of network monitoring and management tools. You should not have to choose whether you want
to review network traffic or network devices. For complete visibility, choose a solution that provides both. When
shopping for the right network analyzer for your network, consider a comprehensive solution for complete
coverage.
