Cisco CNS Network Registrar User's Guide, 6.0
Appendix: SNMP Notification
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SNMP Notification

Table Of Contents

SNMP Notification

How Notification Works

Handling Notification Events

Low Disk Space SNMP Trap

SNMP Troubleshooting

SNMP Notification

The Cisco CNS Network Registrar Simple Network Management Protocol (SNMP) notification support allows you to be warned of error conditions and possible problems with the Network Registrar DNS and DHCP servers, and to monitor threshold conditions that may indicate failure or impending failure conditions.

How Notification Works

Network Registrar SNMP notification support allows a standard SNMP management station to receive notification messages from the two servers. These messages contain the details of the event that triggered the SNMP trap.

Network Registrar generates notifications in response to predetermined events that are detected and signaled by the application code. In addition to the knowledge that a particular event occurred, each event can also carry with it a particular set of parameters or current values. For example, the free-address-low-threshold event may occur within the FDDI-Devices scope with a value of 10 percent free. Other scopes and values are also possible for such an event and each type of event may have different parameters associated with it.

Table E-1 describes the events that can generate notifications.

Table E-1 Notification Events 


Address conflict with another DHCP server detected

Notification when an address conflict with another DHCP server is detected.

Configuration mismatch

Notification when a configuration mismatch between DHCP failover partners occurs.

DNS queue becomes full

Notification when the DHCP server's DNS queue fills and the DHCP server stops processing requests. This is a rare internal condition.

Duplicate IP address detected

Notification whenever a duplicate IP address is detected.

Change in free address count

The free-address-low trap when the number of free IP addresses becomes less than or equal to the low threshold; or a free-address-high trap when the number of free IP addresses exceeds the high threshold after having previously triggered the free-address-low trap.

Other server not responding

Notification when another server (DHCP, DNS, or LDAP) stops responding to the DHCP server.

Other server responding

Notification when another server (DHCP, DNS, or LDAP) responds after having been unresponsive.

Server start

Notification whenever the DHCP or DNS server is started or re-initialized.

Server stop

Notification whenever the DHCP or DNS server is stopped.

Handling Notification Events

When Network Registrar generates a notification, a single copy of the notification is transmitted as an SNMP Trap Protocol Data Unit (PDU) to each recipient. The list of recipients and other notification configuration information are shared by all events (and scopes) and are read when the server is initialized.

Using the CLI

You configure notifications using the trap command. The notification configuration information is persistent and is re-initialized when you run the reload command on the respective server. For more information about configuring notifications, see the trap command section in the Network Registrar CLI Reference Guide.

To use SNMP notifications on your system, you must specify trap recipients. These recipients indicate where Network Registrar notifications are directed. By default, all notifications are enabled, but no trap recipients are defined. Until you define the recipients, no notifications are sent. For details about adding recipients, see the trap addRecipient, listRecipients, and removeRecipient command sections in the Network Registrar CLI Reference Guide.

Network Registrar implements SNMP Trap PDUs according to the SNMP v1 standard. Each trap PDU contains:

Generic-notification code, if enterprise-specific.

Specific-notification field that contains a code indicating the event or threshold crossing that has occurred.

Variable-bindings field that contains additional information about certain events.

Refer to the Management Information Base (MIB) for the details. You can find the MIB in the locations based on the operating system in the following subsections. The MIB requires these MIB files to compile:

These individual Management Information Bases (MIBs) are available at this public website:

MIB Location on UNIX


MIB Location on Windows

\Program Files\Network Registrar\Misc\ 

Low Disk Space SNMP Trap

The Network Registrar mcdshadow utility generates a new SNMP trap if the utility cannot create a shadow backup of the data due to inadequate disk space. See the "Checking MCD Database Integrity" section.

SNMP Troubleshooting

To diagnose Network Registrar conditions, set the following SNMP traps using the CLI. These traps ensure that a central monitor is informed when unexpected events occur, so that you can respond more quickly before things become critical.

nrcmd> trap show 
100 Ok
address-conflict = enabled
dhcp-failover-config-mismatch = enabled
dns-queue-too-big = enabled
duplicate-address = enabled
free-address-high = enabled
free-address-high-threshold = 20%
free-address-low = enabled
free-address-low-threshold = 20%
other-server-not-responding = enabled
other-server-responding = enabled
server-start = enabled
server-stop = enabled
nrcmd> trap enable address-conflict 
100 Ok
nrcmd> trap enable dhcp-failover-config-mismatch 
100 Ok
nrcmd> trap enable other-server-not-responding 
100 Ok
nrcmd> trap enable free-address-low 
100 Ok
nrcmd> trap set free-address-low-threshold=15% 
100 Ok
nrcmd> trap set free-address-high-threshold=30% 
100 Ok

You can also set these traps:

nrcmd> trap enable server-start 
100 Ok
nrcmd> trap enable server-stop 
100 Ok
nrcmd> trap enable free-address-high 
100 Ok
nrcmd> trap enable dns-queue-too-big 
100 Ok
nrcmd> trap enable other-server-responding 
100 Ok
nrcmd> trap enable duplicate-address 
100 Ok

The free-address traps catch when the number of free IP addresses on a server falls below a certain threshold, and when to notify that they again move out of this area. You arm the traps using the trap enable free-address-low and trap enable free-address-high commands. You set the thresholds for each using the trap set free-address-low-threshold and trap set free-address-high-threshold commands, respectively. You set the low and high threshold values either by an absolute number, or by a percentage (followed by the percent sign). You must use the same unit of measure for both thresholds; for example, if the low threshold value is a percentage, the high threshold value must be as well. The free-address-low trap catches when the free addresses fall below the low threshold. The free-address-high trap catches when they are no longer too low. The high value must be equal to or greater than the low one. Both values default to 20 percent. These traps, like all others, apply on a server and not a scope by scope basis.

You generally set the low and high thresholds at a certain offset. For example, you can set the low value to 20%, in which case the DHCP server catches when the number of free addresses fall below 20%. You can then set the high threshold to 25% so that you get a notification at a slightly higher point that the addresses have again become free. As soon as the DHCP server issues a trap for one threshold condition, it arms the trap for the opposite condition. Because of this, creating a safety zone between the two thresholds eliminates issuing traps each time the free addresses hover close to and keep crossing the low threshold point.

Even if you disable one trap through the trap disable command, Network Registrar still sends its opposite as needed.