With IPHost Network Monitor you can run simple snmp requests against a D-Link device in your network.
swRadiusServerEntry
Switch Radius Server Entry
1.3.6.1.4.1.171.12.3.2.4.1
The entiries of raidus Server table
Back to DLINK-AUTH-MIB MIB page.
IPHost Network monitor allows you to monitor swRadiusServerEntry on D-Link device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring D-Link routers right now.