Docker subnet CIDR
docker network subnet cidr · bridge network ip range · docker compose subnet calculator
Pick non-overlapping /16 for local compose stacks.
By DN01 Network Team
Pick non-overlapping /16 for local compose stacks. This guide covers docker subnet cidr with the DN01 IP Calculator — paste CIDR notation or an address plus mask and read network, broadcast, host range, and wildcard fields instantly.
Students and operators searching «docker network subnet cidr» usually need quick verification during networking labs, DHCP planning, or cloud subnet design. Open /en/ip-calculator, enter your prefix, and compare the result grid against your worksheet or runbook.
Subnet math on exams still matters — the calculator confirms homework and production CIDR plans. Pair with the DNS Checker at /en/dns-checker when hostname resolution is in scope, and use /en/api-register-access to automate CIDR validation in CI pipelines.
Docker bridge network CIDR
Docker's default bridge uses 172.17.0.0/16; docker compose projects can specify custom subnets. Pick a /16 that does not collide with corporate 172.16.0.0/12 VPN routes.
Each compose stack should document its bridge CIDR in README — future merges cause mysterious connectivity failures when two projects pick 172.18.0.0/16 independently.
Use ${IP_TOOL} to list network, broadcast, and host capacity before assigning static container IPs.
Step-by-step with IP Calculator
Step 1 — Open /en/ip-calculator and enter CIDR (for example 192.168.1.0/24) or separate IP and subnet mask fields depending on the lab question.
Step 2 — Read network address, broadcast address, first and last usable host, total and usable host counts, dotted-decimal mask, and wildcard mask from the output table.
Step 3 — For Docker subnet CIDR, verify your manual bitmask work matches the tool. Screenshot the grid for lab reports; export via API for Terraform or Kubernetes CIDR guardrails.
Common subnetting mistakes
Publishing the same host port from two compose networks with overlapping subnets.
Assuming host networking mode inherits Docker bridge CIDR rules — it does not.
Ignoring IPv6 docker networks when enabling dual stack.
When to recalculate the subnet
When adding a new compose stack to a developer laptop fleet.
Before enabling Kubernetes-in-Docker (kind, k3d) with custom pod subnets.
During CI runner image updates that change default bridge settings.
Frequently asked questions
- How do I use the calculator for «docker network subnet cidr»?
Paste CIDR or IP+mask at /en/ip-calculator. The tool returns network, broadcast, host range, and mask fields used in CCNA-style worksheets and cloud RFC 1918 planning.
- Why does /31 show two usable hosts?
RFC 3021 allows point-to-point /31 links without a traditional broadcast address. DN01 labels usable counts per prefix length — read the hint row for /31 and /32.
- Can Docker subnet CIDR replace learning binary masks?
No — instructors still expect manual bitmask conversion on exams. Use the calculator to verify answers and catch off-by-one host range errors before submitting labs.
- Can I automate subnet checks?
Register at /en/api-register-access and call the IP calculator API from CI to validate security group CIDRs, Docker compose subnets, and Kubernetes pod CIDR non-overlap.
- Does DN01 store my CIDR inputs?
Recent checks may appear in session history for convenience. For repeatable infrastructure tests, use the API with your own token and log outputs in your pipeline.