The MPLS Topology Server relates VRFs and RouteTargets through the Imports/ImportedBy and Exports/ExportedBy relationship sets, and then discovers which interfaces are associated with each VRF. RouteTargets are used to identify peering relationships between VRFs and to identify different Layer 3 VPN types (full-mesh, hub-and-spoke).
Some computed relationships for VRFs are:
VRF relationship SendsRoutesTo
Points from a VRF to all other VRFs that import a RouteTarget that this VRF exports. The other VRFs get route advertisements from this VRF by having a route target on their import list that matches a route target on this VRF’s export list.
VRF relationship ReceivesRoutesFrom
Points from a VRF to all other VRFs that export a RouteTarget that this VRF imports. The other VRFs advertise routes to this VRF by having a route target on their export list that matches a route target on this VRF’s import list.
VRF relationship VPNPeer
Points from a VRF to all other VRFs that are related to this VRF by both SendsRoutesTo and ReceivesRoutesFrom.
VRF relationship CEs
Points from a VRF to the CE or multi-VRF CE device attached to this VRF.
VRF relationship HostedBy
Relates a VRF to the PE device that is hosting this VRF.