Diagnostics-only BGP troubleshooting patterns for neighbor state, route exchange, prefix policy, AS path inspection, and safe evidence collection.
This skill provides diagnostics-only BGP troubleshooting patterns for situations where a BGP session is down, flapping, established with missing routes, or advertising unexpected prefixes. It solves the problem of triaging BGP issues safely by defaulting to read-only evidence collection, keeping policy changes and session resets confined to a reviewed change window. It covers neighbor state, route exchange, prefix policy, AS path inspection, and careful evidence collection so operators can diagnose before touching configuration.
The read-only triage flow first identifies the exact neighbor, address family, VRF, and local and remote ASNs, then captures summary state and last reset reason, proves reachability to the peer source, checks route policy references, and compares advertised, received, and installed routes where supported. It supplies concrete command sets such as show bgp summary, show bgp neighbors <peer>, show ip prefix-list, show route-map, ping and traceroute with a source, and AS-path regex like show bgp regexp _65001_. A state interpretation table maps states such as Established, Active, Connect, OpenSent/OpenConfirm, and Idle to first checks, and a Python parser using a compiled BGP_SUMMARY_RE regex is included to turn summary output into structured rows while advising that raw output be retained because formats vary by platform.
The skill targets network engineers and operators troubleshooting BGP, as well as those reviewing automation that parses BGP summary output. It stresses change-window-only actions, including clearing a session, changing authentication, timers, update source, route-maps, or prefix-lists, enabling additional received-route storage, and relaxing firewall or ACL policy, and if a reset is approved it prefers the least disruptive soft or route-refresh option. It also lists anti-patterns, such as assuming Active means the remote side is down, ignoring VRF or address-family differences, using broad AS-path regex without token boundaries, and treating missing received-routes output as proof no routes arrived.
When a BGP session is down, flapping, established with missing routes, or advertising unexpected prefixes, or when you need before/after evidence for a BGP change or are reviewing automation that parses BGP summary output.
Yes. The default workflow is read-only evidence collection. Policy and reset actions belong in a reviewed change window and are not suggested as automatic diagnostics.
Identify the exact neighbor, address family, VRF, and local/remote ASNs; capture summary state and last reset reason; prove reachability to the peer source; check route policy references; and compare advertised, received, and installed routes where the platform supports it.
Clearing a BGP session, changing neighbor authentication, timers, update source, route-maps, or prefix-lists, enabling additional received-route storage, and relaxing firewall, ACL, or control-plane policy. If a reset is approved, prefer the least disruptive soft or route-refresh option.
Yes: assuming Active always means the remote side is down, ignoring VRF or address-family or update-source differences, using broad AS-path regex without token boundaries, hard-resetting a peer before reading the last reset reason and logs, and treating missing received-routes output as proof no routes arrived.
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