[Networking issue] Cannot ping remote server from within Docker container

Docker Desktop
1

Hello, everyone,

I’m reaching you as last resort with an issue that I am trying to fix for the last 2 days. I covered all the similar issues from Stackoverflow and this forum that I could find, but was still not able to solve my issue.

[PROBLEM]

  • I have a remote server with an SQL Server instance that I can reach using a VPN
  • I can ping it with no problems from my local machine
  • As soon as I enter my Docker container I cannot ping it anymore, with the ping error message “Destination Host Unreachable”
  • Since I cannot even ping it, I am not able to access the SQL Server database within the server
  • I am not an IT guy so my knowledge of Networking and related deep stuff is very short

[MORE INFORMATION]

  • I can ping successfully the VPN root server within the container.
  • I can ping successfully other web servers with the container, such as the IP 8.8.8.8.
  • I can ping the server within the WSL.
  • I’m running my Docker container using docker-compose and already added “network_mode:host”, with no success
  • I also tried an example docker image from a colleague who was able to ping the remote server and I could not ping it as well, what suggests me that the problem might be some local setting that I am missing

I am running the following Docker version:
Client: Docker Engine - Community
Cloud integration: 1.0.4
Version: 20.10.0
API version: 1.41
Go version: go1.13.15
Git commit: 7287ab3
Built: Tue Dec 8 18:55:31 2020
OS/Arch: windows/amd64
Context: default
Experimental: true

Server: Docker Engine - Community
Engine:
Version: 20.10.0
API version: 1.41 (minimum version 1.12)
Go version: go1.13.15
Git commit: eeddea2
Built: Tue Dec 8 18:58:04 2020
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: v1.4.3
GitCommit: 269548fa27e0089a8b8278fc4fc781d7f65a939b
runc:
Version: 1.0.0-rc92
GitCommit: ff819c7e9184c13b7c2607fe6c30ae19403a7aff
docker-init:
Version: 0.19.0
GitCommit: de40ad0

It may be a very obvious thing I am missing, since I am new to Docker.

Thank you very much in advance and hope you can help me.

Best regards

2

Solved the problem.

The problem was related with the default subnet of Docker, that intercepted the subnet that I was trying to reach.

The first default subnet of docker is: 172.18.0.0/16

You can change it by editing the daemon.json that you can find in the directory “Users\username.docker\daemon.json” and adding the parameter:
“default-address-pools” : [
{
“base” : “172.31.0.0/16”,
“size” : 24
}