Inspect neighbor phase, LSR retransmission lists, relevant LSAs and interface loss. This check would diagnose OSPF LSDB synchronization failure, but would not first isolate the described OSPF totally stub area inter-area constraint. Begin with: Inspect area type, ABR default LSA and the expected absent inter-area summaries.

Check area stub configuration on all routers, Type 3 default and any local ASBR attempts. This check would diagnose OSPF stub area external LSA constraint, but would not first isolate the described OSPF totally stub area inter-area constraint. Begin with: Inspect area type, ABR default LSA and the expected absent inter-area summaries.

Inspect Level-2 LSDBs, adjacency levels, attached bits and inter-area route tables. This check would diagnose IS-IS level-2 backbone continuity, but would not first isolate the described OSPF totally stub area inter-area constraint. Begin with: Inspect area type, ABR default LSA and the expected absent inter-area summaries.

Correct the route propagation or erroneous AS_PATH modification while retaining normal loop prevention. This is a legitimate response to the different issue of BGP AS_PATH loop detection, but it does not correct the specific OSPF NSSA type-7 translation condition reported. The relevant technical distinction is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

Align OSPF Hello and Dead intervals on both ends with the approved link policy. This is a legitimate response to the different issue of OSPF hello and dead timer mismatch, but it does not correct the specific OSPF NSSA type-7 translation condition reported. The relevant technical distinction is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

Apply a narrow supported Level-2-to-Level-1 route-leak policy only for authorized service prefixes. This is a legitimate response to the different issue of IS-IS selective L2-to-L1 route leaking, but it does not correct the specific OSPF NSSA type-7 translation condition reported. The relevant technical distinction is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

Both peers report synchronized link-state contents and calculate the same viable topology. That observation would support a separate case of IS-IS CSNP and PSNP database sync, not verification of the reported OSPF NSSA type-7 translation. The relevant observable outcome here is: The NSSA carries the Type 7 route and eligible outside areas learn its translated external prefix.

Both routers report Full and their relevant area LSDBs are synchronized. That observation would support a separate case of OSPF LSDB synchronization failure, not verification of the reported OSPF NSSA type-7 translation. The relevant observable outcome here is: The NSSA carries the Type 7 route and eligible outside areas learn its translated external prefix.

Branch routers use the correct default/inter-area reachability without forbidden Type 5 LSAs inside the stub. That observation would support a separate case of OSPF stub area external LSA constraint, not verification of the reported OSPF NSSA type-7 translation. The relevant observable outcome here is: The NSSA carries the Type 7 route and eligible outside areas learn its translated external prefix.

An ordinary iBGP speaker does not re-advertise iBGP-learned routes to other iBGP peers. This explains iBGP split-horizon route propagation, but not why the issue in this scenario occurs. The specific mechanism is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

OSPF LSAs and neighbor identities use router IDs that must uniquely identify routers in the routing domain. This explains OSPF duplicate router IDs, but not why the issue in this scenario occurs. The specific mechanism is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

OSPF ABRs convey eligible inter-area reachability through network summary LSAs. This explains OSPF type-3 inter-area summaries, but not why the issue in this scenario occurs. The specific mechanism is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

Resetting an otherwise correct OSPF process cannot solve a persistent interface MTU discrepancy. This consequence is associated more directly with OSPF MTU stalls ExStart. For the stated conditions the immediate exposure is: Replacing a working NSSA with a stub would block intended local external redistribution.

Mismatched metric styles can hide prefixes or distort shortest-path selection. This consequence is associated more directly with IS-IS metric-style consistency. For the stated conditions the immediate exposure is: Replacing a working NSSA with a stub would block intended local external redistribution.

Mismatched neighbor timers can leave a functioning IP link without dynamic routes. This consequence is associated more directly with OSPF hello and dead timer mismatch. For the stated conditions the immediate exposure is: Replacing a working NSSA with a stub would block intended local external redistribution.

Check attached bits in LSPs, candidate L1/L2 routes and default forwarding behavior. This check would diagnose IS-IS L1 default to nearest attached L1L2, but would not first isolate the described OSPF NSSA type-7 translation. Begin with: Trace Type 7 advertisements, P-bit or translation selection and Type 5 LSAs outside the NSSA.

Inspect area type, ABR default LSA and the expected absent inter-area summaries. This check would diagnose OSPF totally stub area inter-area constraint, but would not first isolate the described OSPF NSSA type-7 translation. Begin with: Trace Type 7 advertisements, P-bit or translation selection and Type 5 LSAs outside the NSSA.

Compare external route type, advertised metric, internal ASBR reachability cost and route selection. This check would diagnose OSPF E1 versus E2 external metric, but would not first isolate the described OSPF NSSA type-7 translation. Begin with: Trace Type 7 advertisements, P-bit or translation selection and Type 5 LSAs outside the NSSA.

Assign a distinct stable OSPF router ID to each device and restart the affected process under change control. This is a legitimate response to the different issue of OSPF duplicate router IDs, but it does not correct the specific OSPF NSSA type-7 translation condition reported. The relevant technical distinction is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

Align supported RP discovery or static RP assignments for matching multicast groups across the domain. This is a legitimate response to the different issue of PIM-SM rendezvous-point mismatch, but it does not correct the specific OSPF NSSA type-7 translation condition reported. The relevant technical distinction is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

Restore an appropriate contiguous Level-2 IS-IS inter-area backbone path and verify level participation. This is a legitimate response to the different issue of IS-IS level-2 backbone continuity, but it does not correct the specific OSPF NSSA type-7 translation condition reported. The relevant technical distinction is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

Branch routers use the correct default/inter-area reachability without forbidden Type 5 LSAs inside the stub. That observation would support a separate case of OSPF stub area external LSA constraint, not verification of the reported OSPF NSSA type-7 translation. The relevant observable outcome here is: The NSSA carries the Type 7 route and eligible outside areas learn its translated external prefix.

External clients reach the authorized translated service and unrelated ports remain denied. That observation would support a separate case of Destination NAT and security-policy pair, not verification of the reported OSPF NSSA type-7 translation. The relevant observable outcome here is: The NSSA carries the Type 7 route and eligible outside areas learn its translated external prefix.

The imported prefixes appear once with intended preference and do not reenter their originating protocol. That observation would support a separate case of Route import feedback loop, not verification of the reported OSPF NSSA type-7 translation. The relevant observable outcome here is: The NSSA carries the Type 7 route and eligible outside areas learn its translated external prefix.

Inter-area OSPF route summarization occurs at ABRs when advertising reachability between areas. This explains OSPF inter-area summarization placement, but not why the issue in this scenario occurs. The specific mechanism is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

BGP ORIGIN ranks IGP ahead of EGP and Incomplete after preceding path-selection rules. This explains BGP origin attribute tie break, but not why the issue in this scenario occurs. The specific mechanism is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

OSPF broadcast networks use a designated router to reduce adjacency and LSA exchange overhead. This explains Broadcast OSPF DR and BDR election, but not why the issue in this scenario occurs. The specific mechanism is: NSSA ASBRs advertise Type 7 external LSAs that an ABR can translate for other OSPF areas.

Assuming a Hello neighbor alone provides a complete topology can create inconsistent routing decisions. This consequence is associated more directly with OSPF LSDB synchronization failure. For the stated conditions the immediate exposure is: Replacing a working NSSA with a stub would block intended local external redistribution.

A healthy adjacency without a consistent LSDB may produce transient wrong paths. This consequence is associated more directly with IS-IS CSNP and PSNP database sync. For the stated conditions the immediate exposure is: Replacing a working NSSA with a stub would block intended local external redistribution.

Misunderstanding E2 treatment can produce asymmetric or longer-than-expected external paths. This consequence is associated more directly with OSPF E1 versus E2 external metric. For the stated conditions the immediate exposure is: Replacing a working NSSA with a stub would block intended local external redistribution.

Inspect OSPF interface network type, DR/BDR identity, priority and per-peer state. This check would diagnose Broadcast OSPF DR and BDR election, but would not first isolate the described OSPF NSSA type-7 translation. Begin with: Trace Type 7 advertisements, P-bit or translation selection and Type 5 LSAs outside the NSSA.

Check area stub configuration on all routers, Type 3 default and any local ASBR attempts. This check would diagnose OSPF stub area external LSA constraint, but would not first isolate the described OSPF NSSA type-7 translation. Begin with: Trace Type 7 advertisements, P-bit or translation selection and Type 5 LSAs outside the NSSA.

Trace protocol origin, import rules, tags, preferences and repeated route updates. This check would diagnose Route import feedback loop, but would not first isolate the described OSPF NSSA type-7 translation. Begin with: Trace Type 7 advertisements, P-bit or translation selection and Type 5 LSAs outside the NSSA.