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Prepend the customer's own ASN on advertisements sent through the backup eBGP peer as appropriate would not apply the intended inbound/local BGP local preference policy consistently within the receiving AS.

Comparing valid BGP AS path lengths at the appropriate decision stage and selecting shorter path when higher priorities tie would not apply the intended inbound/local BGP local preference policy consistently within the receiving AS.

Applying an appropriate Cisco-local BGP weight policy on the chosen router without expecting it to propagate to peers would not apply the intended inbound/local BGP local preference policy consistently within the receiving AS.

This test measures a different behavior: Check advertised-routes from the local neighbor and confirm private RFC1918 entries are absent. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect `show bgp` best-path attributes and verify the higher local-preference path is chosen.

This test measures a different behavior: Inspect local weight and best-path choice, then confirm neighboring iBGP routers do not inherit that weight. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect `show bgp` best-path attributes and verify the higher local-preference path is chosen.

This test measures a different behavior: Inspect the AS_PATH actually advertised to backup and primary providers. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect `show bgp` best-path attributes and verify the higher local-preference path is chosen.

That diagnosis is supported by a different symptom: Traffic chooses the longer provider path although all higher-priority attributes tie and the shorter path is eligible. Here the recorded observation is: an engineer predicts the shorter AS_PATH must win although another route has higher LOCAL_PREF. The applicable cause is: bGP preference order evaluates higher LOCAL_PREF before AS path length when otherwise eligible.

That diagnosis is supported by a different symptom: An operator expects a change to local Cisco weight to alter all routers' best paths. Here the recorded observation is: an engineer predicts the shorter AS_PATH must win although another route has higher LOCAL_PREF. The applicable cause is: bGP preference order evaluates higher LOCAL_PREF before AS path length when otherwise eligible.

That diagnosis is supported by a different symptom: The backup provider receives an equally short AS_PATH and incoming traffic does not prefer the primary as intended. Here the recorded observation is: an engineer predicts the shorter AS_PATH must win although another route has higher LOCAL_PREF. The applicable cause is: bGP preference order evaluates higher LOCAL_PREF before AS path length when otherwise eligible.

That control reduces a separate risk: BGP weight is locally significant and is not advertised in BGP updates. For the described design, the recurring risk arises from: bGP preference order evaluates higher LOCAL_PREF before AS path length when otherwise eligible. The specific required safeguard is: document attribute precedence and propagation scope in routing policy reviews.

AS-path length is considered only after higher-priority BGP selection attributes; it does not override the specified LOCAL_PREF policy.

AS-path prepending influences received paths elsewhere, not the inbound local-preference decision the receiving AS must enforce.

Prepend the customer's own ASN on advertisements sent through the backup eBGP peer as appropriate would not apply an explicit outbound BGP prefix list or route-map advertising only approved public networks.

Applying the intended inbound/local BGP local preference policy consistently within the receiving AS would not apply an explicit outbound BGP prefix list or route-map advertising only approved public networks.

Configuring the neighbor address with the correct remote autonomous-system number and reachable interface source would not apply an explicit outbound BGP prefix list or route-map advertising only approved public networks.

This test measures a different behavior: Verify TCP179 and BGP Established state plus exchanged prefixes on both routers. It does not establish the target outcome. For the documented fault, the direct acceptance test is: check advertised-routes from the local neighbor and confirm private RFC1918 entries are absent.

This test measures a different behavior: Inspect `show bgp` best-path attributes and verify the higher local-preference path is chosen. It does not establish the target outcome. For the documented fault, the direct acceptance test is: check advertised-routes from the local neighbor and confirm private RFC1918 entries are absent.

This test measures a different behavior: Inspect the AS_PATH actually advertised to backup and primary providers. It does not establish the target outcome. For the documented fault, the direct acceptance test is: check advertised-routes from the local neighbor and confirm private RFC1918 entries are absent.

That diagnosis is supported by a different symptom: The backup provider receives an equally short AS_PATH and incoming traffic does not prefer the primary as intended. Here the recorded observation is: internal 10.0.0.0/8 summaries appear in a third-party eBGP peer's received table. The applicable cause is: the BGP outbound advertisement policy does not restrict routes to the approved customer prefix set.

That diagnosis is supported by a different symptom: An engineer predicts the shorter AS_PATH must win although another route has higher LOCAL_PREF. Here the recorded observation is: internal 10.0.0.0/8 summaries appear in a third-party eBGP peer's received table. The applicable cause is: the BGP outbound advertisement policy does not restrict routes to the approved customer prefix set.

That diagnosis is supported by a different symptom: The eBGP peer remains in Active because the remote-as is configured as the same local AS. Here the recorded observation is: internal 10.0.0.0/8 summaries appear in a third-party eBGP peer's received table. The applicable cause is: the BGP outbound advertisement policy does not restrict routes to the approved customer prefix set.

That control reduces a separate risk: BGP preference order evaluates higher LOCAL_PREF before AS path length when otherwise eligible. For the described design, the recurring risk arises from: the BGP outbound advertisement policy does not restrict routes to the approved customer prefix set. The specific required safeguard is: require advertised-prefix diffs and peer max-prefix limits during policy modifications.

That control reduces a separate risk: The neighbor AS setting does not match the actual external peer ASN. For the described design, the recurring risk arises from: the BGP outbound advertisement policy does not restrict routes to the approved customer prefix set. The specific required safeguard is: require advertised-prefix diffs and peer max-prefix limits during policy modifications.

That control reduces a separate risk: No AS_PATH length distinction was created on the backup advertisement. For the described design, the recurring risk arises from: the BGP outbound advertisement policy does not restrict routes to the approved customer prefix set. The specific required safeguard is: require advertised-prefix diffs and peer max-prefix limits during policy modifications.

Applying the intended inbound/local BGP local preference policy consistently within the receiving AS would not meet the need for valid BGP AS path lengths at the appropriate decision stage.

Restoring next-hop reachability through appropriate IGP/static routing or supported next-hop-self policy where required would not meet the need for valid BGP AS path lengths at the appropriate decision stage.

Interpreting lower MED as preferable in its applicable comparison scope after more-preferred BGP attributes tie would not meet the need for valid BGP AS path lengths at the appropriate decision stage.

This test measures a different behavior: Inspect local weight and best-path choice, then confirm neighboring iBGP routers do not inherit that weight. It does not establish the target outcome. For the documented fault, the direct acceptance test is: read BGP path attributes and best-path result for the two alternatives.

This test measures a different behavior: Inspect the advertised MED attributes, tie-break prerequisites and selected route. It does not establish the target outcome. For the documented fault, the direct acceptance test is: read BGP path attributes and best-path result for the two alternatives.

This test measures a different behavior: Check BGP next-hop resolution and RIB installation of the previously ineligible prefix. It does not establish the target outcome. For the documented fault, the direct acceptance test is: read BGP path attributes and best-path result for the two alternatives.

That diagnosis is supported by a different symptom: The route with higher MED is chosen because the operator assumes MED acts as larger-is-better. Here the recorded observation is: traffic chooses the longer provider path although all higher-priority attributes tie and the shorter path is eligible. The applicable cause is: an intentional AS-path prepend on the shorter provider made it appear longer to the receiver.

That diagnosis is supported by a different symptom: An engineer predicts the shorter AS_PATH must win although another route has higher LOCAL_PREF. Here the recorded observation is: traffic chooses the longer provider path although all higher-priority attributes tie and the shorter path is eligible. The applicable cause is: an intentional AS-path prepend on the shorter provider made it appear longer to the receiver.

That diagnosis is supported by a different symptom: `show bgp` displays a received network but no usable installed route due to inaccessible next hop. Here the recorded observation is: traffic chooses the longer provider path although all higher-priority attributes tie and the shorter path is eligible. The applicable cause is: an intentional AS-path prepend on the shorter provider made it appear longer to the receiver.