With IPHost Network Monitor you can run simple snmp requests against a D-Link device in your network.
swProtocolVLANencap
Switch Protocol VLA Nencap
1.3.6.1.4.1.171.12.16.1.1.1.6
If protocol type is protocol-userDefined(16),this value will fill with the encap type. Other protocol type, this value will be ignored. The group encap type includes ethernet(1), llc(2), snap(3),and all(4).
Back to SWPROTOCOLVLAN-MIB MIB page.
IPHost Network monitor allows you to monitor swProtocolVLANencap 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.