OSPF has the ability to announce node Entropy Label Capability (ELC), the Maximum Segment Depth (MSD) for node Entropy Readable Label Depth (ERLD), and the Maximum Segment Depth (MSD) for node Base MPLS Imposition (BMI). If needed, exporting these OSPF extensions into BGP-LS requires no additional configuration. These extensions are standardized through draft-ietf-ospf-mpls-elc-12, Signaling Entropy Label Capability and Entropy Readable Label-stack Depth Using OSPF, and RFC 8476, Signaling Maximum SID Depth (MSD) Using OSPF.
The ELC, ERLD, and BMI OSPF values are announced automatically when entropy and segment routing is enabled on the router. The following configuration logic is used:
ELC is automatically announced for host prefixes associated with a node SID when segment-routing and segment-routing entropy-label are enabled for OSPF.
The router maximum node ERLD is announced for OSPF when segment-routing and segment-routing entropy-label is enabled together with advertise-router-capability.
The router maximum node MSD-BMI for OSPF is announced when segment-routing advertise-router-capability are enabled.
Exporting ELC, MSD-ERLD and MSD-BMI OSPF extensions into BGP-LS encoding occurs automatically when database-export for BGP-LS is configured.
The announced value for maximum node MSD-ERLD and MSD-BMI can be modified to a smaller number using the override-bmi and override-erld commands. This can be useful when services (such as EVPN) or more complex link protocols (such as Q-in-Q) are deployed. Provisioning correct ERLD and BMI values helps controllers and local-cspf to construct valid segment routing label stacks to be deployed in the network.
Segment routing parameters are configured in the following context:
configure>router>ospf>segment-routing
configure>router>ospf>segment-routing>override-bmi value
configure>router>ospf>segment-routing>override-erld value