Classless inter-domain routing
Classless Inter-Domain Routing is an IP addressing and routing scheme that represents networks and address ranges with a network prefix and prefix length.
Acing the Certified Kubernetes Administrator Exam, Second Edition
CIDR is a notation for specifying IP address ranges using a network address and prefix length.
- How it is used
- Configures and verifies Kubernetes address ranges, especially the Service CIDR used by CoreDNS and ClusterIP Services.
- How deep it goes
- Defines node, Pod, and Service ranges, then demonstrates Service-CIDR reconfiguration through kubelet updates and DNS verification.
- Examples
- Uses 100.96.0.0/16, kube-dns at 100.96.0.10, /etc/resolv.conf, and nslookup as concrete verification artifacts.
- What you can do after
- Operate/configure a Kubernetes Service CIDR and verify Pod DNS resolution with kubectl, kubelet configuration, and nslookup.
Microsoft Azure in Action
Classless Inter-Domain Routing is an IP addressing and routing method that uses prefix lengths to define variable-sized address ranges.
- How it is used
- Defines precise address ranges for Azure VNets and subnets.
- How deep it goes
- Explains address-mask structure, binary AND, host counts, and Azure reservations, then stops short of broader routing mechanics.
- Examples
- Uses 10.1.0.8/16, the 10.1.0.0–10.1.255.255 range, and a PowerShell 10.0.1.0/24 subnet configuration.
- What you can do after
- Operate/configure Azure subnet ranges and estimate their address capacity before provisioning networks.
Read how Microsoft Azure in Action explains classless inter-domain routing →
Google Anthos in Action
A CIDR block is an IP address range represented with Classless Inter-Domain Routing prefix notation.
- How it is used
- Plans non-overlapping address pools for nodes, Pods, and Services in Anthos GKE clusters.
- How deep it goes
- Calculates subnet masks from node and Pod capacity, including a worked /11 example.
- Examples
- Uses 5,000 nodes, 110 Pods per node, /24 node allocations, and a calculated /11 Pod range.
- What you can do after
- Apply CIDR sizing tables and formulas to allocate cluster address ranges.
Read how Google Anthos in Action explains classless inter-domain routing →
Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu
A CIDR block is a compact notation for an IP network and the range of addresses it contains.
- How it is used
- Uses CIDR to divide cloud networks into Terraform-managed public, private, and isolated subnets.
- How deep it goes
- Explains IPv4 prefixes, bit-based subdivision, masks, ranges, and Terraform calls, then stops short of provider-wide networking design.
- Examples
- Demonstrates 192.168.0.0/16, four /18 ranges, cidrsubnet console calls, and Terraform public-private subnet modules.
- What you can do after
- Configure Terraform subnet layouts by deriving nonoverlapping CIDR blocks and routing private traffic through NAT.
Acing the CCNA Exam: Volume 1 Fundamentals and Protocols
CIDR notation is slash notation that expresses an IP address's network prefix length.
- How it is used
- Uses flexible prefix lengths to allocate IPv4 address blocks efficiently and divide them into appropriately sized subnets.
- How deep it goes
- Explains slash notation, subnet creation, address calculations, FLSM, VLSM, and point-to-point prefixes.
- Examples
- Uses 192.168.1.0/24 subdivisions and compares /24, /25, /26, /27, and /28 address-block sizes.
- What you can do after
- Apply CIDR notation to divide IPv4 address blocks and calculate subnet counts, address ranges, and usable hosts.
Related concepts
- classful networkingcontrasts with · Classful networking is an IPv4 addressing architecture based on the fixed network boundaries and default prefix lengths of address classes A, B, and C.
- INET data typeused by · INET is a database data type for storing IPv4 and IPv6 host addresses.
- netmaskuses · A netmask is a bit mask that distinguishes the network portion of an IP address from its host portion.
- IP addressconfigures · An IP address is a numerical address used by the Internet Protocol to identify a network interface and support packet delivery across networks.
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