In Junos, static routes are eligible to be exported into dynamic routing protocols if you configure an export policy that matches them. For management-only routes, especially default routes or specific management subnets used for out-of-band access, you often want to ensure they never leak into the production routing domain. The no-readvertise parameter is designed for this purpose. When you mark a static route as no-readvertise, Junos flags it so other routing protocols do not export or readvertise it, even if an export policy would otherwise match it. This helps keep the management plane isolated from the data plane and prevents accidental propagation of management reachability into the fabric underlay or overlay.

The reject and discard options control how packets are handled if they match the route, not whether the route is eligible to be exported. Preference 255 changes the route’s selection priority relative to other routes, but it does not prevent export. Therefore, no-readvertise is the correct configuration knob when the explicit goal is to prevent propagation of a management static route to other routers.