e-BGP is used as the routing protocol in the data center underlay.

Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

In many SR Linux data center fabrics, eBGP is used in the underlay because it gives simple hop-by-hop routing, fast convergence, and clean autonomous-system separation between leaf and spine nodes. The EVPN overlay, however, is a separate MP-BGP control plane used to distribute EVPN NLRI. The overlay route-reflector session does not have to reuse the leaf's underlay autonomous system number. In practice, an overlay BGP group may use a distinct local AS or configuration model separate from the underlay AS design. Therefore, option B is false. The route reflector's cluster ID is configured on the route reflector itself to prevent reflection loops and identify the RR cluster. Redundant route reflectors can be deployed for resiliency, and clients may receive duplicate paths or duplicate updates from multiple RRs; the BGP decision process and route reflection rules handle this. The key design distinction is that underlay eBGP provides IP reachability between loopbacks, while overlay MP-BGP EVPN carries tenant service reachability. Mixing these roles leads to incorrect AS planning. Reference: SR Linux EVPN MP-BGP route reflectors, eBGP underlay, overlay BGP sessions.

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