BGP best path selection differs due to arrival order tiebreaker #55
Description
Problem
BGP RIB validation fails because Batfish and device show different best paths due to arrival order tiebreaking, causing next-hop IP mismatches in iBGP advertisements.
Technical Details
In BGP best path selection, when all other tiebreakers are equal, arrival order determines the best path. Batfish may model a different arrival order than what occurred in the actual network, leading to different best path selection and different next-hop IPs being advertised to iBGP peers.
Observed In
traditional_dc_T105
Symptoms
- BGP RIB routes showing different next-hop IPs between Batfish and device data
- Best path selection discrepancies in multipath scenarios
- iBGP route advertisements with incorrect next-hop information
Configuration Patterns
BGP configurations with multiple equal-cost paths where arrival order determines best path selection
Next Steps
Investigation needed into handling arrival order dependencies in BGP best path validation, potentially requiring validation logic that accounts for legitimate arrival order variations