connect EHOSTUNREACH 172.24.0.2:27017 docker-compose

Question

I am currently unable to connect to mongo when I run docker-compose, I keep on getting the error below

connect EHOSTUNREACH 172.25.0.2:27017

Here is my docker-compose.yml file

version: "3.4"
services: 
    app:
        container_name: checki
        restart: always
        build:
          context: .
          network: host
        ports: 
          - "3000:9000"
        links: 
          - mongo
    mongo:
        container_name: mongo
        image: mongo
        volumes:
          - ./data:/data/db
        ports: 
          - "27018:27017"

and my db connection string is like this

"mongodb://mongo:27017/checki"

Please assist