Cloud Interconnect and VPN both connect your on-premises environment to Google Cloud Platform (GCP), but they operate at different levels and offer distinct trade-offs in terms of performance, cost, and complexity.
Imagine you’re sending a critical package. A VPN is like a secure tunnel through the public internet. It’s encrypted, so nobody can snoop on the contents, but it’s still subject to the whims of internet traffic. Cloud Interconnect, on the other hand, is like building a dedicated, private highway directly from your loading dock to the GCP warehouse.
Let’s look at how these play out in practice.
Cloud VPN
Cloud VPN uses IPsec to create encrypted tunnels over the public internet. It’s the most common way to get started connecting on-prem to GCP.
Use Case: For many organizations, Cloud VPN is the sweet spot. It’s cost-effective, relatively easy to set up, and provides a secure connection. The primary limitation is performance: you’re sharing bandwidth with the rest of the internet, so throughput can be variable and latency can be higher.
Configuration Example:
Let’s say you have an on-prem router with the IP 1.2.3.4 and you want to connect to a GCP VPC network with the subnet 10.10.0.0/24.
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GCP Side (VPC Network):
- Create a VPC network if you don’t have one.
- Create a Cloud VPN Gateway in the region you want to connect from. Let’s say
us-central1. - Create a VPN Tunnel and associate it with your Cloud VPN Gateway. You’ll specify the remote peer IP (
1.2.3.4) and the shared secret (a strong passphrase). - Configure static routes in your GCP VPC to direct traffic destined for your on-prem network (
192.168.1.0/24) through the VPN tunnel.
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On-Prem Side:
- Configure your on-prem router to establish an IPsec tunnel with the GCP VPN Gateway’s public IP address. You’ll need to match the encryption and authentication algorithms (e.g., AES256, SHA256, DH Group 14) and the pre-shared key (the same shared secret).
- Configure your on-prem firewall to allow IPsec traffic (UDP ports 500 and 4500) and ESP protocol.
- Add routes on your on-prem network to direct traffic destined for your GCP VPC subnet (
10.10.0.0/24) through the VPN tunnel.
How it Works: IPsec encrypts your data packets and encapsulates them within UDP packets. These UDP packets travel over the internet to the GCP VPN Gateway, which decrypts them and forwards them to your VPC. The process is reversed for traffic going from GCP to on-prem.
Common Pitfall: Network Address Translation (NAT) on your on-prem side can interfere with IPsec. Ensure your VPN gateway’s public IP is directly reachable, and that no NAT is happening between your VPN device and the GCP VPN Gateway.
Cloud Interconnect
Cloud Interconnect offers direct, private connections from your data center to Google’s network. It bypasses the public internet entirely.
There are two primary types:
- Dedicated Interconnect: You provision a physical cross-connect from your on-prem data center to a Google Point of Presence (PoP). This is for high-bandwidth, low-latency needs.
- Partner Interconnect: You connect through a supported service provider (e.g., Equinix, AT&T) who has a direct connection to Google’s network. This is more flexible if you don’t have a data center near a Google PoP or need less bandwidth.
Use Case: Cloud Interconnect is for mission-critical workloads where predictable performance, higher bandwidth, and lower latency are paramount. Think large-scale data transfers, hybrid cloud applications requiring near real-time communication, or scenarios where internet-based VPNs are simply too unreliable or slow.
Configuration Example (Dedicated Interconnect):
Let’s assume you’ve ordered a 10 Gbps Dedicated Interconnect connection.
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Physical Connection:
- You’ll work with Google to identify a suitable Google PoP.
- You’ll order a cross-connect from your colocation facility (or your on-prem network if it’s adjacent to a PoP) to the Google equipment at that PoP. This involves physical cabling.
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GCP Side (VPC Network):
- Create a VPC network if you don’t have one.
- Create a VLAN attachment for your Interconnect connection. You’ll specify the capacity (e.g., 10 Gbps), the Cloud Router you want to use for BGP, and the on-prem router’s BGP IP address.
- Create a Cloud Router in the region of your VLAN attachment. This router will handle the Border Gateway Protocol (BGP) peering with your on-prem router.
- Configure dynamic routes (via BGP) on your Cloud Router to advertise your GCP subnets to your on-prem network, and to receive on-prem routes.
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On-Prem Side:
- Configure your on-prem router to establish a BGP peering session with the Cloud Router’s BGP IP address. You’ll use an Autonomous System Number (ASN) for your on-prem network (e.g., 65001) and the one provided by Google for the Cloud Router (e.g., 64512).
- Ensure your on-prem router is configured to advertise your on-prem subnets to GCP.
- Configure your on-prem firewall to allow BGP traffic (TCP port 179) from the Cloud Router’s IP address.
How it Works: Cloud Interconnect uses BGP to exchange routing information between your on-prem network and GCP. Traffic flows over the dedicated private link, not the public internet. This provides a more stable, predictable, and higher-throughput connection.
The One Thing Most People Don’t Know: When you use Cloud Interconnect with BGP, you’re not just getting a pipe; you’re integrating your network’s routing intelligence directly with Google’s. This means GCP can learn about your on-prem network topology dynamically, and your on-prem routers can learn about your GCP VPC subnets. You can even influence route selection by manipulating BGP attributes like MED (Multi-Exit Discriminator) or local preference, effectively telling your on-prem network which GCP regions or services are preferred for certain traffic.
The next challenge you’ll likely encounter is optimizing traffic flow and ensuring redundancy across multiple Interconnects or VPNs.