Download Controlling the Amount of Traffic Generated by NNM

Controlling the Amount of Traffic Generated by NNM
When you configure performance reports using the NNM web Reporting interface, the data collector starts
collecting data. This data collection increases network traffic. You cannot control when or how frequently the
collections are taken. If you need to reduce the amount of network traffic, you can suspend the generation of the
report. See the NNM online help for more information.
Network Node Manager software automatically generates intense polling traffic at first as the network monitoring process is
discovering your network.
After NNM's initial discovery of your network, you are in control of NNM's polling based upon your business needs. There are
five types of polling in NNM that you need to know about. You can customize polling, or you can turn polling off completely.
There are benefits and consequences to your decisions: less polling means less network traffic; however, reducing the amount
of polling traffic by lengthening polling intervals may delay real-time map updates, resulting in a less accurate map and less
timely alarm logs. Turning polling off completely disables proactive management of your network.
You adjust NNM's polling through two dialog boxes accessed with the map menu's Options:SNMP Configuration and
Options:Network Polling Configuration menu items.
Figure 1 Options:SNMP Configuration Dialog Box
Check the online help from these dialog boxes for more detailed information than you will find in this chapter. The five types
of polling are:
 Status polling ( Status Polling) This is an ICMP ping sent to each interface of each managed device to verify if it is
still accessible by the management station. In addition, a direct SNMP poll checks cached port tables on hubs and
bridges to find the physical address listings of non-SNMP supported devices, and a direct SNMP poll updates the
designated list of DHCP addresses. Only management stations running the Windows NT operating system: IPX
diagnostic requests are also sent. The default interval is once every 5 minutes for each managed device.
Level-2 devices (without their own IP address) whose physical addresses were found in cached port tables are
included in NNM's databases and displayed on the map. However, no network polling traffic is generated on
behalf of these devices.

Configuration check polling ( Configuration-Check Polling) This is an SNMP poll to gather current information
about managed devices. This information is used by NNM to keep the maps current. The default interval is once-per24-hours for each managed device.

Topology check polling of connecting devices ( Connector Topology Polling) This is an SNMP poll to verify the
manner in which managed connective devices (bridges and hubs via the Bridge MIB, Repeater MIB, and proprietary
HP MIBs) service other devices on the network. The default interval is 4 hours.

New node discovery polling ( New Node Discovery Polling (IP, Level-2, and IPX)) There are two categories of new
node discovery, IP and IPX. IP is an SNMP poll that scans for previously unknown devices and updates the map. The
default interval is dynamic. Only management stations running the Windows NT operating system: if the IPX stack is
configured as part of your Windows NT operating system, IPX issues RIP, SAP, and IPX diagnostic commands to
detect additions to your management domain.
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Secondary failures polling ( Secondary Failure Polling) This status polling works in conjunction with the EventCorrelation feature provided with NNM. During a network failure, NNM now identifies the device causing the
problem and correlates failure messages from all other affected devices. Through this setting, you control how long
NNM ignores devices other than the primary failure. You can also instruct NNM to never ignore certain critical
devices, even if they are a secondary failure in an event stream.
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Also see suggestions for fine-tuning all of these polling settings on Fine-Tuning the Polling Services.
Status Polling
For each managed IP device, an ICMP ping is issued to verify if it is still accessible by the management station. The default
interval for IP devices is once every 5 minutes. Often, the default setting of 5 minutes for every device is not optimal. Refer to
the list of mission-critical devices that you developed in Planning Your NNM Configuration You will probably want to poll
mission-critical devices more frequently. Some customers decide not to poll certain devices at all, such as end-user PCs or
certain printers.
Dynamic Host Configuration Protocol (DHCP) allows IP addresses to be allocated on a temporary basis (a lease). When the
lease for an IP address expires, the address can be reused by a different node. This is useful in environments supporting mobile
users who connect to the network with a laptop from many different places.
You can specify the range of IP addresses that your network is configured to assign dynamically for mobile devices. The
default is OFF (no filter in use). If this filter is enabled, NNM keeps the map clean and the Alarm Browser list free of
unnecessary messages about devices within this address range as they are repeatedly attached and detached from your network.
Addresses are defined through a filter that you write using Boolean logic. See A Guide to Scalability and Distribution for
information about writing, testing, and implementing the DHCP filter.
You can control status polling in the following ways.
In the Options:SNMP Configuration dialog box
 Set polling intervals on specific nodes by IP address, IPX address, or hostname.
For IP addresses only, you can set polling intervals using IP address wildcards for a group of IP nodes (for example,
15.122.*.*). You can also import a file that contains your configuration preferences; see the online help in this
dialog box for information about using a file. The IP address wildcard is useful; for example, when you want to
configure different values for time-outs or the number of retries for Wide Area Networks (WANs).

Set the status polling interval to be used for any device not specifically listed. If you set it to 24-hours, polling begins
at the time that you enter the setting. The actual time may drift depending on network conditions.

Specify time-out and retry values. For example, you may want to increase the time-out and retry count values to
prevent the management station from a premature time-out when making requests across a WAN because latency
times are greater over WANs than LANs. Note that the time-out value is set in tenths of a second, and the time-out
value doubles with each retry.
In the Options:Network Polling Configuration dialog box
 Turn OFF/ON both IP and IPX status polling.

Specify the interval of time that NNM should wait before deleting a "down node" from your maps. The default is 1
week.

Identify your DHCP node list filter to specify a group of IP addresses that NNM should use for laptop computers.
NNM handles this group of IP addresses differently, since devices will be connected and disconnected often from
these addresses. Also specify the time interval that NNM should wait before deleting a disconnected node from your
map.

Designate your Discovery filter (if you created a filter of devices that should be excluded from polling). See Create a
Discovery Filter Identifying Which Devices to Include.
Configuration-Check Polling
This type of polling gathers SNMP information about all currently managed devices for NNM's exclusive use. Configurationcheck polling gathers information such as:
 Contact and location change

Forwarding IP packets change

Interface added

Interface deleted

Incorrect routing by a node

Link address change

Mismatch of link address

Network mask change

Node name change

Object Identifier change

Mismatches in link addresses
 World wide web capabilities
This information is used by NNM to keep the maps and databases current. The default interval is once-per-24-hours. This
setting applies to all managed devices; it cannot be customized per node.
You can control configuration-check polling in the following ways.
In the Options:Network Polling Configuration dialog box
 Turn OFF/ON all configuration polling.

Set the interval of time to wait between configuration polling, starting from the time that you set it. The time may drift
depending on network conditions.
Connector Topology Polling
Connector topology polling monitors how hubs and bridges are connected in a network. All hubs and bridges are polled based
upon the Bridge MIB (RFC1493), Repeater MIB (RFC2108), MAU MIB (RFC1515), and proprietary HP MIBs. You cannot
set this polling on a per node basis. This setting helps keep your map current when you are moving devices around.
You can control connector topology polling in the following ways.
In the Options:Network Polling Configuration dialog box
 Turn it OFF/ON.

Specify the interval of time. The default is 4 hours.
New Node Discovery Polling (IP, Level-2, and IPX)
New node discovery polling checks available ARP caches and Routing tables. This information is used to keep your maps
current. This setting applies to all managed devices. It cannot be customized per node.
If you are running NNM on a Windows NT management station: For each managed IPX network, the following broadcasts
occur for each discovery interval. The default interval is 6 hours:
 A single broadcast IPX Routing Information Protocol (RIP) request

Two broadcast Service Advertising Protocol (SAP) requests
 Two broadcast IPX diagnostic requests per network, 10 seconds apart
You can control new node discovery polling in the following ways.
In the Options:Network Polling Configuration dialog box
For IP and Level-2 devices:
 Turn new node discovery polling OFF/ON. The default is ON for both IP and Level-2 devices.

Select either the auto-adjust discovery interval or set your own polling interval. The default is auto-adjust, which is
based upon the number of new nodes discovered. The range is between 15 minutes and 24 hours.
For IPX devices:
 Turn new-node discovery polling OFF/ON. The default is OFF.

Set your polling interval or the desired specific time of day for polling.

Specify the maximum number of sequential routers through which to poll. The default hop count is zero.
Secondary Failure Polling
This setting allows you to fine-tune the behavior of the connector-down correlation circuit. The default is ON. See NNM's
Event Correlation System and Connector Down Correlation System for more information about the event correlation feature.
You can control secondary failure polling in the following ways.
In the Options:Network Polling Configuration dialog box
 Turn secondary failure polling OFF/ON.

Specify the factor by which the normal polling interval should be extended for secondary devices during a failure.

Designate the section that you wrote in the filters file that specifies which critical devices should always be
excluded from the secondary status list regardless of their location during a failure event.

Control the behavior of the map and event log during a failure event.
Fine-Tuning the Polling Services
The amount of network management traffic generated by status polling depends on your network's configuration, including:
 How many nodes are up and how many are down?

How many nodes are on the same subnet?

How many nodes are on other subnets?

How large is the permanent ARP cache?
 How probable is it that a particular IP address can be found in the permanent ARP cache?
Polling is controlled by NNM's netmon service (background process). Because automatic polling is based upon managed
nodes, you can reduce the amount of network-management traffic by unmanaging nodes. Simply select the node or nodes on
the map, and then select the Edit:Unmanage Objects menu item. You can add nodes and change nodes from
unmanaged to managed. It may take a while for polling changes to take effect. Polling is scheduled on a per node basis, but the
netmon service can fall behind schedule if its polling load exceeds capacity limits.
To automatically set specific types of devices to unmanaged, such as all printers or all end-user systems, see the
oid_to_type reference page in NNM's online help (or the UNIX manpage). See also Modify the oid_to_type File to
Unmanage Devices by Type.
To determine if the polling process is overloaded, select the Performance:Network Polling Statistics menu
item. If "Seconds until next status poll" or "Seconds until next SNMP poll" is a negative number, then the polling queue is
overloaded and running behind.
If polling is continually running behind, you may want to change the startup parameter settings in the netmon.lrf file for
queue length (-q controls the ICMP queue length and -Q controls the SNMP queue length). The default queue setting is 3 on a
management station running the Windows NT operating system and 20 on a management station running a UNIX operating
system. Increasing queue length affects the management station's use of system resources and use of network bandwidth for
network management.
For information about parameter choices available to you for configuring NNM's polling service:
 See the netmon reference page in NNM's online help (or the UNIX manpage) for a wealth of choices about
controlling polling from the command line and start-up parameter settings. The information in this reference page lists
the parameters allowed in the netmon.lrf file. See Create a Seed File Specifying Multiple IP Networks to Manage
for information about the process of changing the netmon.lrf file (the seed file requires a modification to the
netmon.lrf file).

See the xnmpolling reference page in NNM's online help (or the UNIX manpage) for information about how to
change polling configuration from the command line.
 See NNM's online help available from within the Options:SNMP Configuration dialog box and the
Options:Network Polling Configuration dialog box for more information.
Information that is gathered during polling is stored in NNM's ovsnmp.conf_db database.
Watching NNM's Polling Queue
You can automate NNM to notify you whenever the netmon service is falling behind in the polling queue.
Use NNM's Data Collection & Thresholds feature (see Data Collection Thresholds) to monitor two MIB values from HP's
netmon MIB (provided on NNM's installation CD; use Load/Unload MIBs to access the netmon MIB):
 nnmICMPSecsUntilNextPoll (.1.3.6.1.4.1.11.2.17.4.4.1.1.3) and
 nnmSNMPSecsUntilNext Poll (.1.3.6.1.4.1.11.2.17.4.4.1.2.3)
Set the threshold configuration to generate a trap each time the polling queue falls behind to the negative amount that you
specify.
Then use NNM's Event Configuration feature ( Event Configuration Overview) to set up Automatic Action instructions for that
trap instructing NNM to email a message to you or to page you each time that trap is received.
Running NNM Without Network Polling
It is possible to run NNM without the netmon service (background process) that polls your network to generate the map and
detect changes. This may be useful if the only applications you have running under NNM do not rely on netmon's discovery
functionality or if you are relying on collection stations to perform discovery and monitoring.
See A Guide to Scalability and Distribution for information about collection stations and how to proceed with this
step when using collection stations.
To run NNM without automatic IP discovery, configuration checking, and polling by netmon, follow these steps:
1. Stop the currently running netmon service (background process). From the command line, type ovstop -v
netmon
2. Remove netmon from NNM's start-up options. At the command prompt, type:
Windows NT: ovdelobj \OpenView\lrf\netmon.lrf
UNIX: ovdelobj $OV_LRF/netmon.lrf
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