Networking Technology

Multi-Cloud Networking Explained: A Beginner's Guide to Connecting Workloads Across Clouds

Updated on
9 min read

Multi-cloud networking refers to the strategic connections formed between workloads, services, and users across multiple cloud providers like AWS, Azure, and Google Cloud, often including on-premises infrastructure. In this beginner’s guide, we will explore essential concepts, architectures, connectivity options, and security considerations. Perfect for entry-level IT professionals, developers, and sysadmins, this article aims to provide a foundational understanding of multi-cloud networking, enabling you to effectively design and manage cloud-connected environments.

Key Concepts & Terminology

Understanding key terminologies is crucial for working effectively within multi-cloud networking:

  • Virtual Networks (VPC, VNet): Cloud providers offer virtual network constructs like AWS VPC, Azure VNet, and GCP VPC, serving as your network boundary. Components such as subnets, routing tables, security groups, NSGs, and network ACLs function within these confines.

  • Peering vs. Transit vs. Hub-and-Spoke:

    • Peering: Direct, low-latency connectivity between two virtual networks. Typically non-transitive, meaning traffic does not automatically pass through one peer to another.
    • Transit/Hub-and-Spoke: A central hub facilitates connections among multiple spokes, enabling transitive routing through a controlled point.

  • Direct Connect / ExpressRoute / Dedicated Interconnect: These are provider-specific private connections linking your infrastructure to the cloud provider, offering lower latency, higher stability, and potentially reduced egress costs compared to using the public internet.

  • VPN (IPsec) and Site-to-Site VPN: Encrypted tunnels over the internet, easy to set up, but subject to jitter and variable latency.

  • SD-WAN and Overlay Networks: Software-defined overlays that combine internet/MPLS links, providing centralized policy control and traffic steering to optimal cloud on-ramps.

  • BGP, Routing & ASN Basics: BGP is used for exchanging routes between networks; an Autonomous System Number (ASN) identifies a routing domain, allowing for dynamic route propagation and failover.

  • CIDR, Subnets, MTU: CIDR notation specifies IP ranges. Avoid CIDR overlaps across connected networks to maintain network efficiency. MTU is critical since IPsec/encapsulation can reduce effective MTU and lead to fragmentation issues.

Why Choose Multi-Cloud? (Benefits & Use Cases)

Adopting a multi-cloud strategy offers several advantages:

  • Avoid Vendor Lock-in: Reduces risk and enhances bargaining power by not depending on a single provider.
  • Best-of-Breed Services: Enables the use of specialized services from different cloud platforms where applicable.
  • Resiliency and Geography: Distributes workloads across regions and providers for disaster recovery and lower latency.
  • Regulatory/Data Residency Compliance: Meets legal requirements for data storage related to specific jurisdictions.
  • Integrating Environments Post-Mergers & Acquisitions: Essential for organizations that inherit varying cloud environments.

Common Challenges & Trade-offs

Despite the benefits, multi-cloud networking presents challenges:

  • Complexity: Increases the number of networks to manage, along with diverse vendor APIs and routing policies.
  • Expanded Security Surface: More endpoints and transit points necessitate robust security measures.
  • Cost: Egress fees, transit gateways, SD-WAN appliances, and partner services can elevate expenses.
  • Operational Overhead: Requires unified monitoring, automation, and consistent change control across clouds.
  • Performance Variability: Internet-based tunnels can lead to jitter and packet loss; private interconnects mitigate these issues but at a higher cost.

Architecture Patterns

Here are common multi-cloud network architectures and their use cases:

1. Point-to-Point VPN (Cloud A ↔ Cloud B)

  • Best For: Small proofs-of-concept and simple, low-traffic links.
  • Pros: Quick and inexpensive.
  • Cons: Non-transitive, not suitable for multiple VPCs/VNets.

2. Hub-and-Spoke (Transit Gateway / Virtual WAN)

3. Full Mesh

  • Best For: Environments with a very small number of networks.
  • Pros: Low-latency connections between specific pairs.
  • Cons: Poor scalability due to complex route management.

4. SD-WAN Overlay to Cloud On-ramps

  • Best For: Organizations with multiple branches.
  • Pros: Centralized policies and traffic steering.
  • Cons: Increases vendor complexity and cost.

5. Hybrid: On-Prem + Multi-Cloud

  • Best For: Environments necessitating coexistence of legacy systems and cloud-native services.

Connectivity Technologies & How They Work

Site-to-Site VPN (IPsec)

  • What: Encrypted tunnels over the internet.
  • When: Ideal for quick deployments, particularly for PoCs and low bandwidth.
  • Drawbacks: Subject to variable latency/jitter; adjust MTU on tunnel endpoints to avoid fragmentation.

Provider Private Connectivity (Direct Connect / ExpressRoute / Interconnect)

  • What: Physical connections between your infrastructure and a cloud provider.
  • When: Necessary for predictable latency and high throughput scenarios.
  • Drawbacks: Involves provisioning time, local presence, and higher costs. Learn more about GCP’s Network Connectivity Center.

Cloud-Native Transit Services

  • Services like AWS Transit Gateway, Azure Virtual WAN, and Google’s Network Connectivity Center facilitate connections among multiple VPCs/VNets and on-prem networks. These services streamline routing, attachments, and integration with VPNs and direct links.

Cloud Peering

  • Connects two VPCs/VNets directly. Usually cost-effective within the same provider but typically non-transitive.

SD-WAN Vendors

  • Companies like Cisco, VMware (VeloCloud), and Fortinet provide software overlays to unify branches and cloud on-ramps. SD-WAN can improve cloud access and can replace MPLS in many setups.

Security & Governance

Effective security practices are paramount:

  • Network Segmentation: Utilize separate VPCs/VNets for different trust zones.
  • Zero Trust Architecture: Enforce explicit authentication and authorization among services.
  • Encryption: Always encrypt sensitive cross-cloud traffic; use IPsec for tunnels and TLS for application traffic.
  • Identity & Access Management: Implement provider IAM best practices and utilize cross-account roles or service principals.
  • Centralized Logging & Monitoring: Use AWS VPC Flow Logs, Azure Network Watcher, and GCP Cloud Audit Logs, integrating with SIEM/SOC.
  • DDoS Protection & WAF: Leverage provider-specific DDoS protections and Web Application Firewall services.
  • Policy-as-Code: Employ Infrastructure as Code (IaC) for managing network policies, ensuring they undergo code reviews in automated pipelines.

Performance Monitoring & Troubleshooting

Monitor the following key metrics:

  • Latency, packet loss, jitter, throughput, and BGP route convergence time.

Tools

  • Built-in: AWS VPC Flow Logs, Azure Network Watcher, GCP’s Network Intelligence Center.
  • Generic: Use tools like ping, traceroute, mtr, and iperf3 for testing throughput and latency.
  • Synthetic Monitoring: Schedule tests between critical endpoints to identify anomalies.

Common Issues & Causes

  • Overlapping CIDRs: Can lead to blackholed or asymmetric routing.
  • BGP Misconfiguration: Pay attention to incorrect ASNs and missing filters.
  • MTU Mismatches: Encapsulation issues can cause fragmentation and dropped traffic.
  • Asymmetric Routing: Multiple internet hops could disrupt stateful firewalls.

Practical Example: Connect an AWS VPC to an Azure VNet using a Site-to-Site VPN

This is a high-level overview; refer to AWS and Azure VPN documentation for complete instructions.

Prerequisites

  • Non-overlapping CIDRs (for instance, AWS VPC 10.1.0.0/16 and Azure VNet 10.2.0.0/16).
  • Administrative access in both environments to create gateways and configure routes.

Steps

  1. Create a Virtual Network and VPN Gateway on Azure.
  2. Establish a Virtual Private Gateway (or Transit Gateway attachment) on AWS.
  3. Set up a Customer Gateway on AWS (representing your Azure VPN gateway public IP) and create a site-to-site VPN connection.
  4. Exchange IPsec/IKE settings or configure BGP for dynamic routing.
  5. Propagate routes on both sides for mutual learning.
  6. Update security groups/NSGs and firewall rules to allow necessary traffic.

Using BGP vs. Static Routes

  • BGP: Recommended for scalability and resiliency, with automatic route exchanges and failover.
  • Static Routes: Simpler but require manual updates; suitable for fixed networks.

Common Pitfalls:

  • Avoid overlapping IP ranges.
  • Mitigate MTU and fragmentation on IPsec tunnels.
  • Ensure matching IKE/IPsec proposals on both sides.
  • Verify inbound rules in security groups/NSGs.

For detailed vendor instructions, consult:

Best Practices & Checklist

Design

  • Plan CIDRs centrally to prevent overlaps.
  • Opt for hub-and-spoke/transit configurations for scalability.
  • Use private interconnects when performance reliability is necessary.

Security

  • Enforce least privilege and Zero Trust principles.
  • Encrypt all cross-cloud traffic and protect management planes.
  • Centralize logging and integrate logs with SIEM.

Automation & Operations

  • Implement IaC (Terraform, CloudFormation, ARM/Bicep) for consistent resource provisioning.
  • Maintain current runbooks and diagrams.

Monitoring & Cost Management

  • Enable flow logs and synthetic tests for critical paths.
  • Observe egress and transit costs to avoid unexpected charges.

Documentation & Training

  • Keep updated network diagrams and troubleshooting playbooks.
  • Consider building a lab for practice using Building a Home Lab.

FAQ

Q: What is the best way to connect two cloud networks?
A: A site-to-site IPsec VPN is simple to set up and provides encryption, making it ideal for proofs-of-concept and low-traffic links.

Q: When should I deploy a transit gateway or virtual WAN?
A: These solutions are suitable for environments with multiple VPCs/VNets, providing centralized routing and security.

Q: Is Direct Connect or ExpressRoute always necessary?
A: Not always; while beneficial for high throughput and predictable latency, they do add costs and require provisioning time.

Q: How can I avoid overlapping IP ranges across cloud environments?
A: Centralize CIDR allocation, utilize private address spaces per environment, or implement NAT where necessary.

Q: Does peering allow traffic to transit through other networks?
A: Generally, no — most provider peering configurations are non-transitive. Use a transit hub for transitive routing instead.

References & Authoritative Documentation

Internal Resources

TBO Editorial

About the Author

TBO Editorial writes about the latest updates about products and services related to Technology, Business, Finance & Lifestyle. Do get in touch if you want to share any useful article with our community.