Cisco Inter-Switch Link (ISL) is a Cisco proprietary protocol that maintains VLAN information as traffic flows between switches and routers.
Observium has specialised support for IPv6 address tracking, VRF and Pseudowire tracking, VLAN tracking via VTP-MIB and QBRIDGE-MIB, BGP session tracking via BGP4-MIB, CISCO-BGP4-MIB and BGP4-V2-MIB-JUNIPER and device inventory tracking via ENTITY-MIB.
Client switches query the VMPS server using the VLAN Query Protocol, or VQP.