What is BGP Route Flapping?
BGP route flapping occurs when BGP sessions repeatedly cycle between Established and Idle states. This causes route withdrawals and re-advertisements, impacting network stability and customer traffic.
Common Causes
- MTU mismatches on transit links
- Interface flaps causing TCP session resets
- CPU/memory exhaustion on the router
- BFD misconfiguration
- MD5 authentication key mismatch
Diagnostic Commands
show bgp summary debug ip bgp 10.0.0.1 events show ip bgp neighbors 10.0.0.1 | include BGP state
Resolution
Check MTU with: ping 10.0.0.1 size 9000 df-bit. If ping fails, you have an MTU issue. Set interface MTU to match the transit link and clear the BGP session.