More networks than the defaults allow
The error that follows reads like a bug rather than a capacity limit
40 networks
Docker Network Subnet Calculator
Two things run out with Docker networking: the number of networks, and the address space itself. Give a count, or the ranges Docker must stay out of, or both.
Paste below, or drop a file anywhere on this panel
Or drop a file anywhere on this panel. Nothing is uploaded: the analysis runs in this tab.
The answer appears here
Paste on the left and press Calculate. Nothing leaves this tab.
Formatted
Results
Nothing else to flag.
No formatting problems, and nothing the rules object to. Worth remembering what that covers: this reads the file you pasted, not the account or cluster it will be applied to.
No finding matches that filter.
Examples
Real input you can load into the tool above. Each one shows a different thing going wrong, because that is what the tool is for.
A range the host also routes
One internal service becomes unreachable and nothing in the application changed
5 networks 172.17.0.0/16
Common mistakes
These are the ones that fail silently. The config is accepted, nothing raises an error, and the consequence arrives later.
Assuming the address pool is effectively unlimited
It is 31 networks, and compose projects consume them one each. The failure appears as an error that reads like a bug rather than a limit.
Instead:Set default-address-pools with a larger base and a smaller size before you need it.
Editing default-address-pools and restarting, then finding nothing changed
The setting applies to networks created afterwards. Existing networks keep their subnets.
Instead:Recreate the affected networks. For docker0 specifically, use bip instead.
Stopping containers instead of bringing the project down
The network stays allocated and keeps counting against the pool, invisibly.
Instead:Use docker compose down, and docker network prune periodically.
The defaults give exactly 31 networks
172.17.0.0/16 through 172.31.0.0/16 is fifteen, and 192.168.0.0/16 carved into /20s is sixteen more. Past that, every network creation fails.
The error does not sound like a capacity limit
"could not find an available, non-overlapping IPv4 address pool among the defaults to assign to the network". It reads like a bug. Every compose project creates a network and only docker compose down removes it, so a build machine reaches the limit far sooner than the number of applications suggests.
172.17.0.0/16 collides with a great many corporate networks
When a Docker network takes a range the host also routes elsewhere, the route to the container network wins. The symptom is one internal service or one VPN subnet becoming unreachable from that machine while everything else works, with nothing having changed in the application.
The fix is default-address-pools in daemon.json
A base of 10.100.0.0/16 with size 24 gives 256 networks in a range almost nothing else claims. Restart the daemon after changing it.
Changing the setting does not move existing networks
It is consulted when a network is created. Existing networks keep their subnets across a restart, so editing the file and restarting appears to do nothing at all, which is where the time on this usually goes.
The default bridge is a special case
docker0 is not created from the pools, so default-address-pools does not move it. That one needs bip in daemon.json, which is the setting people miss after fixing everything else.
Networks leak from projects that were not brought down
Deleting a project directory, or stopping containers by hand, leaves the network allocated and counting against the pool. docker network ls on a busy machine is usually a long list of networks nothing is using.
More docker tools
Docker Container Image Reference Parser Is that a registry or a Docker Hub user? Dockerfile Linter What this image will do to you later docker run to Kubernetes YAML And the flags that have no equivalent Docker Compose to Kubernetes And why depends_on has no equivalent Docker Logging Driver Generator json-file never rotates Dockerfile Non-Root USER Generator Numeric, or Kubernetes rejects it Docker OCI Image Labels Generator One of them actually does something Docker Hub Pull Rate Limit Calculator Counted per IP, not per person Docker Registry Storage Calculator Deleting a tag frees nothing Docker Build Context Analyzer All of it uploads before anything runs Docker Compose to docker run Converter Names stop resolving Docker Compose Version Migrator version: is obsolete now Docker Compose Network and Port Viewer Everything reaches everything Docker Command Explainer Which flags hand over the host Docker BuildKit Cache Mount Generator apt deletes the cache you just mounted Docker BuildKit Secret Mount Generator ARG is in docker history forever Docker .dockerignore Pattern Tester *.log does not match logs/app.log Docker Image Manifest Viewer unknown/unknown is not broken Docker Image Config Viewer Anyone who can pull can read your Env Docker Registry Token Decoder Check the scope before the credentials Docker HEALTHCHECK Generator Docker does nothing when it fails Docker History Analyzer The rm did not save anything Docker Run to Compose Converter Some flags have no equivalent Docker CMD and ENTRYPOINT Tester Why docker stop takes ten seconds Docker Port Mapping Tester -p reaches past your firewall Docker -v to --mount Converter -v invents missing directories Docker Restart Policy Simulator The backoff resets after ten seconds Docker Exit Code Explainer 137 is two different problems Docker CPU Limit Converter --cpu-shares limits nothing Docker Memory Limit Calculator -m 512m allows a gigabyte Docker Compose Interpolation Tester An unset variable is an empty string Docker Environment Variable Precedence Tester Your shell does not reach the container Docker Compose Override Merge Previewer An override can add a port, never remove one Dockerfile Multi-Stage Build Analyzer Which stages reach the image Dockerignore Validator It is not .gitignore