You're encountering a known behavior of GCP's Cloud Router, which does ECMP (Equal-Cost Multi-Path) routing by default when multiple BGP paths are considered equal — and unfortunately, GCP does not support a manual preference or prioritization between multiple BGP routes learned for the same prefix.
✅ Here's what you need to know and do:
🧠 Key Behavior:
GCP always load-balances outbound traffic if two BGP paths are considered equal.
GCP ignores MED, AS path, Local Preference, and prepending when deciding route preference between different Cloud Routers — it only considers:
Prefix length (more specific preferred),
Static vs dynamic (static preferred),
Route type (peering, direct, etc.),
And then it uses ECMP if they're still equal.
🔧 Goal: Prefer One Interconnect Path, Use Second as Failover
To achieve this, you must ensure only one Cloud Router advertises the route at any given time.
✅ Use selective advertisement on-prem
On your on-prem router:
Advertise the route to only one Cloud Router at a time.
Only advertise to the second one when the primary is down (e.g., with conditional advertisements or BGP route-maps based on reachability).
✅ Pros: Simple and effective
❌ Cons: Requires changes on-prem
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