VPC Networking

A Virtual Private Cloud (VPC) is a logically isolated network on IBM Cloud where you deploy your compute, storage, and database resources. VPC networking gives you full control over IP addressing, subnets, routing, and security.

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What is a VPC?

A VPC provides:

• Isolation — your resources are logically separated from other tenants
• Control — you define the IP address ranges, subnets, and routing
• Security — use security groups and ACLs to control traffic
• Scalability — spans multiple availability zones within a region

Every VPC exists within a single IBM Cloud region.

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VPC Components

Address Prefixes

When creating a VPC, you define address prefixes (CIDR blocks) for each zone:

Zone	Address Prefix	Usable IPs
us-south-1	10.240.0.0/18	~16,000
us-south-2	10.240.64.0/18	~16,000
us-south-3	10.240.128.0/18	~16,000

Subnets

A subnet is a range of IP addresses within a zone:

• Each subnet belongs to a single availability zone
• Has its own CIDR block (subset of the address prefix)
• Attached to a network ACL for traffic control

VPC: my-vpc
├── Subnet: web-subnet-1 (us-south-1, 10.240.0.0/24)  → Public
├── Subnet: web-subnet-2 (us-south-2, 10.240.64.0/24) → Public
├── Subnet: app-subnet-1 (us-south-1, 10.240.1.0/24)  → Private
└── Subnet: db-subnet-1  (us-south-1, 10.240.2.0/24)  → Private

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Internet Connectivity

Public Gateway

A public gateway provides outbound-only internet access for an entire subnet:

• Resources in the subnet can reach the internet
• The internet cannot initiate connections to the resources
• One public gateway per zone

Floating IPs

A floating IP is a static public IP address you can assign to a specific instance:

• Enables both inbound and outbound internet access
• Persists independently of the instance lifecycle
• Useful for jump boxes, NAT instances, or public-facing servers

Load Balancers

IBM Cloud VPC offers two types of load balancers:

Type	Description	Use Case
Application Load Balancer (ALB)	Layer 7 (HTTP/HTTPS) load balancing	Web applications, microservices
Network Load Balancer (NLB)	Layer 4 (TCP/UDP) load balancing	High-throughput, low-latency workloads

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Security

Security Groups

Virtual firewalls at the instance level:

• Stateful (return traffic automatically allowed)
• Allow rules only
• Applied to individual network interfaces
• Default: deny all inbound, allow all outbound