During the postprocessing phase of discovery, the MPLS Topology Server creates an “UnderlyingVPN” relationship between the discovered BGP services/ BGP protocol endpoints/ BGP sessions and the VPNs that are discovered during L3VPN discovery:
BGPService --> UnderlyingVPN --> VPN
BGPProtocolEndpoint --> Underlying --> VPN
- BGPSession --> UnderlyingVPN --> VPN
The UnderlyingVPN relationship is what makes MPLS-BGP cross-domain correlation possible. It enables the MPLS Topology Server to generate VPN-impacted events for underlying BGP sessions that are impacted by BGP failures, misconfigurations, or manually disabled BGP protocol endpoints.