Cloud interconnect is used to connect your in-house infrastructure to Google Cloud Platform. Cloud Interconnect provides us with Interconnect and Peering services, with Interconnect having a Dedicated Interconnect and IPsec. In Interconnect, your in-house infra is connected to GCP VPC dedicatedly. And IPsec on the other hand, connects your in-house infra with Cloud VPC using IPsec VPN. It provides direct access to RFC1918 IPs, with an SLA.
Now, in Peering Connection, we have Direct Peering and Carrier Peering. Direct Peering and Carrier gives you access to Google's public IP, but without an SLA.
When to use:
The following figure shows when to go for Direct Peering, Carrier Peering, Dedicated Interconnect, or IPsec VPN: ...
