You can limit admin users' login to a set of IP addresses, this feature is turned off by default.

To enable it:

Login to your DPOD as root user
Start app-util.sh and stop the UI service via the "Stop Service" menu option (note: this will logoff all existing users)
Edit the file /app/ui/MonTier-UI/conf/MonTierUI.conf
Search for the configuration property security.limit.admin.ip
The property's value may contain:
blank - turned off, no check will be performed
a specific IP - like 10.0.0.9
an IP range surrounded with square brackets - For example 10.0.0.[100-200] , 10.0.[0-220].[0-255] or 128.[10-17].0.5
a list of IPs and IP ranges, use comma as a separator- 10.0.0.1, 10.0.0.3, 10.0.[10-20].[0-255]

Entering an invalid value for the security.limit.admin.ip property will prevent the UI service from starting
Save the file
Start app-util.sh and start the UI service via the "Start Service" menu option

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