Scenario
A peering stays up after a provider change but one business-critical prefix set no longer enters the local table.
A BGP session remains Established while one route class vanishes because the route-map depends on communities the upstream stopped exporting
Control-plane health looks perfect, yet policy still breaks for part of the table because the attributes it relies on are no longer present.
What to check first
- Identify the primary failure signal in the Healthy Session, Broken Policy Contract scenario.
- Separate visible symptoms from the underlying technical dependency.
- Describe the safest recovery path and the follow-up prevention work.
Checking checklist
- Summarize the current impact and the last known change.
- Collect direct evidence from logs, runtime state, and configuration before changing anything.
- Separate immediate recovery from permanent prevention work.
Recovery and prevention
Validate the route attribute contract with the upstream before rewriting local filtering.
Questions worth viewing together
Community-field BGP problem inspired by operator and Cisco Community posts about missing routes after upstream community changes. An Established session proves reachability, not that policy-relevant attributes stayed stable.
Teams often suspect route dampening or timers when the upstream simply changed which communities it exports.
Route policies that depend on external community contracts need periodic revalidation.
Similar cases seen in the field