GCP Cloud Router
When VPC is created, GCP automatically deploys a GCP Cloud Router (CR) to route between different subnets. GCP Cloud Router (CR) runs as a service by default.
CR is similar to a traditional router. It is only the control plane device
It learns route from on-prem. It is only BGP speaker (no OSPF).
Every VM is doing host routing. All the VMs in GCP route table lives on VM itself.
VM route directly to the IP address.
It is google managed process. GCP will re spin the cloud router. It is like a distributed router. GCP will bring that back up.
When you setup VPC
Two routing mode
Only learns in the specific region. CR-West only learn in West.
set it up at the VPC level. Global routing allows to pick all subnets
subnets in the west and east. it is very powerful. VPCs are global by nature. You put cloud router in some regions and then it learns globally
Global vs Regioanl constructs.
Comes down to LB. When yoi have LB. LB is regional. Then it means use regional Router instead of Global region,
Route Priority (MED)
Is actully MED in GCP. Standrd MED is 1000
Local CR will have MED of 1000.
Routes from other regions have a metric based on RTT added to the default MED value