ERROR: Pool overlaps with other one on this address space

I'm trying to implement this tutorial. The "docker-compose" content is this :

 # WARNING: Do not deploy this tutorial configuration directly to a production environment
#
# The tutorial docker-compose files have not been written for production deployment and will not 
# scale. A proper architecture has been sacrificed to keep the narrative focused on the learning 
# goals, they are just used to deploy everything onto a single Docker machine. All FIWARE components 
# are running at full debug and extra ports have been exposed to allow for direct calls to services. 
# They also contain various obvious security flaws - passwords in plain text, no load balancing,
# no use of HTTPS and so on. 
# 
# This is all to avoid the need of multiple machines, generating certificates, encrypting secrets
# and so on, purely so that a single docker-compose file can be read as an example to build on, 
# not use directly. 
# 
# When deploying to a production environment, please refer to the Helm Repository
# for FIWARE Components in order to scale up to a proper architecture:
# 
# see: https://github.com/FIWARE/helm-charts/
#
version: "3.5"
services:
  # Orion is the context broker
  orion:
    image: fiware/orion:latest
    hostname: orion
    container_name: fiware-orion
    depends_on:
        - mongo-db
    networks:
        - default
    expose:
        - "1026"
    ports:
        - "1026:1026"
    command: -dbhost mongo-db -logLevel DEBUG
    healthcheck:
      test: curl --fail -s http://orion:1026/version || exit 1
      interval: 5s
  # Tutorial displays a web app to manipulate the context directly
  
  tutorial:
    image: fiware/tutorials.context-provider
    hostname: iot-sensors
    container_name: fiware-tutorial
    networks:
        - default
    expose:
        - "3000"
        - "3001"
    ports:
        - "3000:3000"
        - "3001:3001"
    environment:
        - "DEBUG=tutorial:*"
        - "PORT=3000"
        - "IOTA_HTTP_HOST=iot-agent"
        - "IOTA_HTTP_PORT=7896"
        - "DUMMY_DEVICES_PORT=3001"
        - "DUMMY_DEVICES_API_KEY=4jggokgpepnvsb2uv4s40d59ov"
        - "DUMMY_DEVICES_TRANSPORT=HTTP"
  iot-agent:
    image: fiware/iotagent-ul:latest
    hostname: iot-agent
    container_name: fiware-iot-agent
    depends_on:
        - mongo-db
    networks:
        - default
    expose:
        - "4041"
        - "7896"
    ports:
        - "4041:4041"
        - "7896:7896"
    environment:
        - "IOTA_CB_HOST=orion"
        - "IOTA_CB_PORT=1026"
        - "IOTA_NORTH_PORT=4041"
        - "IOTA_REGISTRY_TYPE=mongodb"
        - "IOTA_LOG_LEVEL=DEBUG"
        - "IOTA_TIMESTAMP=true"
        - "IOTA_MONGO_HOST=mongo-db"
        - "IOTA_MONGO_PORT=27017"
        - "IOTA_MONGO_DB=iotagentul"
        - "IOTA_HTTP_PORT=7896"
        - "IOTA_PROVIDER_URL=http://iot-agent:4041"
 # Database
  mongo-db:
    image: mongo:3.6
    hostname: mongo-db
    container_name: db-mongo
    expose:
        - "27017"
    ports:
        - "27017:27017"
    networks:
        - default
    command: --bind_ip_all --smallfiles
    volumes:
      - mongo-db:/data
    healthcheck:
      test: |
        host=`hostname --ip-address || echo '127.0.0.1'`; 
        mongo --quiet $host/test --eval 'quit(db.runCommand({ ping: 1 }).ok ? 0 : 2)' && echo 0 || echo 1
      interval: 5s
      
networks:
  default:
    ipam:
      config:
        - subnet: 172.18.1.0/24
volumes:
  mongo-db: ~

But when I run the docker compose with the command "docker-compose up -d" I get this error :

*WARNING: The host variable is not set. Defaulting to a blank string.
Creating network "fiware_default" with the default driver
ERROR: Pool overlaps with other one on this address space*

I also get these networks by running the command "docker network ls" :

*NETWORK ID     NAME            DRIVER    SCOPE
78403834b9bd   bridge          bridge    local
1dc5b7d0534b   hadig_default   bridge    local
4162244c37b0   host            host      local
ac5a94a89bde   none            null      local*

I see no conflict with the name "fiware_default". where is the problem?

The "pool" the error message refers to is the 172.18.1.0/24 CIDR block that file manually specifies. If something else on your system is using that network space, it won't start up. (Docker might have assigned another Compose file's network to 172.18.0.0/16, for example.)

You don't usually need to manually specify IP addresses in Docker at all, and so you should remove that ipam: block. Having done that, you're telling Compose to configure the default network with default settings, and you can actually remove the entire networks: block at the end of the file.

The exception to this is if your host network environment is using some of the same IP address blocks, and then you do potentially need an override like this. If you run ifconfig or a similar command from the host (or look at your host's network settings from a desktop application) and your host or a VPN is using a 172.18.1.* address, you'll also get this message. In that case, change the network to something else; if you only need a /24 (254 addresses) then setting subnet: 192.168.123.0/24 (where "123" can be any number between 1 and 254) should get you past this.