DHCP alerts notify an administrator when dynamic address usage within a DHCP range or shared network is unusually low or exceptionally high.
When the ratio of free-to-allocated addresses falls below or rises above administrator-defined watermarks, Address Manager will send an alert in the form of an email message and/or an SNMP trap. If you are using a shared network in DHCP, a DHCP alert notification for all networks inside the shared network will be sent as a single entity notification using the DHCP alert set at the configuration level. DHCP alerts for each individual network within any shared network will also be sent only if object-specific DHCP alerts are set at the network or DHCPv4 range level.
You can configure DHCP alert settings globally at the configuration level. These global settings are inherited by all DHCP ranges, IP blocks, and networks in any configuration. You can also configure object-specific DHCP alert settings to override the global settings at the block, network, or DHCPv4 range level.
- DHCP alerts can be viewed in the Event List, filtering for the "DHCP Alert Service" event type. For details, refer to Viewing DHCP alert notifications.
- For DHCP alerts to be forwarded to users, you must configure the Event Notification Service. For more information, refer to Managing Notification Groups.
To configure DHCP alert settings:
- Select the Administration tab. Tabs remember the page you last worked on, so select the tab again to ensure you're on the Administration page.
- Under Network, click DHCP Alert Settings.
Under Watermarks, set the Host
Density watermark values:
Note: HD-Ratio is calculated per RFC 3194, the Host-Density Ratio for Address Assignment Efficiency. For more information, refer to http://tools.ietf.org/html/rfc3194.
- HD-Ratio Low Watermark—triggers an alert when DHCP usage falls below this value (when too few addresses are being used).
- HD-Ratio High Watermark—triggers an alert when a DHCP usage rises above this value (when too many addresses are being used).
Under Frequency, determine the frequency at which the
alert service should poll DHCP usage levels:
In the Frequency Time Value fields, type a value and select a time interval (Seconds, Minutes, Hours, or Days) from the drop-down menu.
- Under Change Control, add comments, if required.
- DHCP Alert notifications DHCP alert notifications are triggered only by a change in DHCP usage. If DHCP pool usage remains in the same position relative to the low/high watermarks of the last execution, a DHCP alert notification will not be sent.
- First execution (that is, the first DHCP alert notification sent out) occurs after a delay of the configured frequency (which is at least 1 hour). As such, any changes to DHCP usage during this time frame will go unnoticed.
- If you set the polling frequency and later change it to a new value, the new value will not take effect until the original polling frequency runs to completion. For example, if you set the polling frequency to 6 hours, and later change it 1 hour, the 1 hour value will not take effect until the first frequency value (6 hours) runs to completion. To circumvent this, you can restart the Address Manager server.