Network & Infrastructure / OSPF & Underlay Convergence
Passive interfaces and missing transit adjacencies after templating
A new automation template removes an underlay neighbor while leaving the connected subnet advertised. A passive interface can originate reachability without participating in neighbor discovery.
Environment and inputs: OSPFv2 IPv4 underlays, with OSPFv3 explicitly identified where used; timers and diagnostics vary by platform. Diagnostic/design example; not tested on production equipment.
Collect the evidence
Compare intended transit and service interfaces with passive-interface defaults and explicit exceptions. Inspect the generated configuration and runtime interface state, not only the address inventory.
Explain the result
Advertising a subnet and forming an adjacency are separate OSPF behaviors. A connected route appearing remotely does not prove the local port is allowed to exchange hellos.
Plan the fix
Define explicit transit-interface membership in the source of truth and render exceptions consistently. Keep service-facing interfaces passive where the design requires no routing neighbors.
Check the result and rollback
Check intended neighbor counts and absence of unexpected adjacencies on user networks. Revert the template if it activates OSPF on untrusted segments or leaves required transit links passive.