Visual Cloud VPC & CIDR Calculator
RFC 4632Compute IPv4 network boundaries, netmasks, wildcard masks, AWS VPC reserved IPs, and child subnet splits.
1. IPv4 Address & CIDR Prefix Length
2. Subnet Splitter (Divide /16 into /18)
| # | Child Subnet CIDR | Usable Host Range | AWS IPs |
|---|---|---|---|
| 1 | 10.0.0.0/18 | 10.0.0.1 - 10.0.63.254 | 16,379 |
| 2 | 10.0.64.0/18 | 10.0.64.1 - 10.0.127.254 | 16,379 |
| 3 | 10.0.128.0/18 | 10.0.128.1 - 10.0.191.254 | 16,379 |
| 4 | 10.0.192.0/18 | 10.0.192.1 - 10.0.255.254 | 16,379 |
# IPv4 CIDR Network Specification (RFC 4632) CIDR Block : 10.0.0.0/16 Network Address : 10.0.0.0 Subnet Mask : 255.255.0.0 Wildcard Mask : 0.0.255.255 Broadcast Address : 10.0.255.255 Binary Netmask : 11111111.11111111.00000000.00000000 # Host Capacity & Cloud VPC Reservations Total IPv4 IPs : 65,536 POSIX Usable Hosts : 65,534 (10.0.0.1 - 10.0.255.254) AWS/GCP Usable IPs : 65,531 (Starts at 10.0.0.4) AWS VPC Router IP : 10.0.0.1 AWS VPC DNS Server : 10.0.0.2 # Subnet Split (/18 Subnets) Subnet #01: 10.0.0.0/18 | Range: 10.0.0.1 - 10.0.63.254 (16,379 AWS IPs) Subnet #02: 10.0.64.0/18 | Range: 10.0.64.1 - 10.0.127.254 (16,379 AWS IPs) Subnet #03: 10.0.128.0/18 | Range: 10.0.128.1 - 10.0.191.254 (16,379 AWS IPs) Subnet #04: 10.0.192.0/18 | Range: 10.0.192.1 - 10.0.255.254 (16,379 AWS IPs)
IPv4 Classless Inter-Domain Routing (RFC 4632) & Cloud VPC Architecture
Classless Inter-Domain Routing (CIDR), standardized in IETF RFC 4632, replaced legacy Class A, B, and C network addressing with variable-length subnet masking (VLSM). A CIDR block is written as an IPv4 address followed by a prefix length between /0 and /32, indicating how many leading bits out of the 32-bit IPv4 integer identify the routing network prefix versus individual host interfaces.
Standard Usable Hosts vs. Cloud VPC Reservations
In traditional on-premises networking, every subnet loses 2 IP addresses: the all-zeros host address (network identifier) and the all-ones host address (directed broadcast). Cloud providers including AWS VPC, Google Cloud VPC, and Azure Virtual Network reserve 5 IP addresses per subnet (the first 4 IPs and the last broadcast IP) for the VPC router, internal DNS resolver, and future DHCP/network extensions.
RFC 1918 Private Address Space Allocations
Private networks and Kubernetes Pod/Service CIDRs must be allocated from RFC 1918 non-routable blocks to prevent BGP route collisions with public internet endpoints: 10.0.0.0/8 (16.7M IPs), 172.16.0.0/12 (1.04M IPs), and 192.168.0.0/16 (65,536 IPs).
Common IPv4 Prefix Reference Table
| CIDR | Subnet Mask | Total IPs | POSIX Usable | AWS VPC Usable |
|---|---|---|---|---|
| /16 | 255.255.0.0 | 65,536 | 65,534 | 65,531 |
| /20 | 255.255.240.0 | 4,096 | 4,094 | 4,091 |
| /24 | 255.255.255.0 | 256 | 254 | 251 |
| /26 | 255.255.255.192 | 64 | 62 | 59 |
| /28 | 255.255.255.240 | 16 | 14 | 11 |