Subnetting Architecture in Cloud & DevOps
Accurately calculating CIDR blocks prevents IP overlap in virtual private clouds (VPCs), hybrid cloud VPN tunnels, and container overlay networks.
Frequently Asked Questions
What is CIDR notation and how does subnetting work?
CIDR (Classless Inter-Domain Routing) specifies an IP address and its subnet mask using a forward slash and bit count (e.g., 192.168.1.0/24). The prefix indicates how many bits are allocated for the network prefix, with the remaining bits used for host addresses.
How many usable IP addresses are in a /24, /16, and /28 subnet?
A /24 subnet has 256 total IPs and 254 usable host addresses. A /16 subnet has 65,536 total IPs and 65,534 usable hosts. A /28 subnet has 16 total IPs and 14 usable hosts (with 2 IPs reserved for Network and Broadcast).
What are the RFC 1918 Private IP address ranges?
The three standard private IPv4 ranges are: 10.0.0.0/8 (10.0.0.0 - 10.255.255.255), 172.16.0.0/12 (172.16.0.0 - 172.31.255.255), and 192.168.0.0/16 (192.168.0.0 - 192.168.255.255).
What is a Wildcard Mask and where is it used?
A Wildcard Mask is the bitwise inverse of the subnet netmask (e.g., 0.0.0.255 for a 255.255.255.0 netmask). It is commonly used in Cisco IOS Access Control Lists (ACLs) and OSPF routing protocols.
Why are the first and last IP addresses in a subnet reserved?
In standard IPv4 networking, the very first IP is the Network Identifier (e.g. 192.168.1.0) and the very last IP is the Subnet Broadcast Address (e.g. 192.168.1.255), which cannot be assigned to individual machines.
How do I calculate subnets for AWS VPC or Kubernetes clusters?
Enter your VPC CIDR (e.g. 10.0.0.0/16) to calculate overall network limits, or design smaller /24 and /28 subnets for private databases and public load balancers.