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Debian Can Connect to Google But Not GitHub? Solutions Here

If you’ve recently installed or updated Debian and found that you’re able to comfortably visit google.com but get stuck when trying to reach GitHub via the terminal or web browser, you’re not alone. This issue has puzzled many developers and sysadmins alike, as it tends to occur without any obvious misconfiguration. In this article, we’ll examine why Debian can connect to Google but has trouble with GitHub, and more importantly, how to fix it.

TL;DR

If Debian can reach google.com but fails to connect to github.com, it’s likely due to DNS resolution issues, firewall or proxy settings, or missing CA certificates. Start by verifying name resolution with dig or nslookup, check your DNS settings, update CA certificates, and ensure no outbound blocking via firewalls or proxies. IPv6 inconsistencies can also play a role—disabling it may help as a temporary measure.

Understanding the Problem

The symptom seems straightforward: Debian successfully pings or accesses Google, but fails when you try something like:

git clone https://github.com/user/repo.git

This might be followed by a failure message such as:

fatal: unable to access 'https://github.com/user/repo.git/': Could not resolve host: github.com

At first glance, it might seem like a GitHub-specific issue, but it typically indicates a problem with network configuration, DNS resolution, or SSL certificate validation.

Potential Causes and Solutions

1. DNS Resolution Failure

One common source of the problem is DNS issues. Debian uses /etc/resolv.conf to determine DNS servers.

Solution:

  • Check DNS resolution with:
    • dig github.com
  • If it fails, try editing /etc/resolv.conf to use Google’s public DNS:
    • nameserver 8.8.8.8
nameserver 8.8.4.4
  • Then retry your GitHub operation.

If you’re using systemd-resolved, also check the output of:

systemd-resolve --status

2. Firewall or Proxy Settings

Sometimes your network (especially enterprise or educational networks) may block access to GitHub but allow access to more general or widely used services like Google.

Solution:

  • Temporarily disable your firewall with:
    • sudo ufw disable
  • Or check iptables rules that may be impacting connectivity:
    • sudo iptables -L
  • If you’re behind a proxy, ensure your http_proxy and https_proxy environment variables are correctly configured:
    • echo $http_proxy
echo $https_proxy

Use unset or correctly export the variables as needed:

export http_proxy=http://your.proxy.server:port
export https_proxy=http://your.proxy.server:port

3. Inconsistent SSL Certificates

GitHub uses strict security settings—including SSL/TLS encryption. If your Debian machine does not have up-to-date certificate authorities, it may not trust GitHub’s certificate chain.

Solution:

  • Ensure the CA certificates are up to date:
    • sudo apt update
sudo apt install --reinstall ca-certificates
sudo update-ca-certificates

Also try this quick test:

curl -v https://github.com

If the certificate is not verified, the output will indicate the SSL error.

4. Using IPv6 in an IPv4 Network

Some servers and ISPs have incomplete or misconfigured IPv6 support. Debian might try to resolve and connect to an IPv6 address for GitHub, while Google has better dual-stack support.

Solution:

To disable IPv6 temporarily (for testing):

sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1
sudo sysctl -w net.ipv6.conf.default.disable_ipv6=1

To disable it permanently, edit /etc/sysctl.conf and add:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1

Then reboot your system and retry accessing GitHub.

5. Testing with Alternative Tools

If the issue isn’t resolved using the above methods, test using various tools to narrow down whether it’s a DNS, connectivity, or SSL issue specific to Git or curl.

Options include:

  • Using wget:
    • wget https://github.com
  • Checking for port blockage:
    • telnet github.com 443
  • Using nc (netcat):
    • nc -zv github.com 443

Special Case: GitHub Over SSH Works But HTTPS Fails

In some environments, cloning over SSH works, but HTTPS cloning fails. This often points to SSL issues or proxies interfering with HTTPS traffic.

Tips:

  • If HTTPS cloning fails, try SSH:
    • git@github.com:user/repo.git
  • Ensure your SSH keys are properly configured in ~/.ssh and uploaded to GitHub.

If this works, the problem likely lies in your HTTPS stack or proxy configuration.

Miscellaneous Network Testing Checklist

  • Check your /etc/hosts file for hardcoded entries
  • Reboot the router or try another internet connection (e.g., using a phone’s hotspot)
  • Use a VPN to tunnel traffic and bypass local or ISP restrictions

Final Thoughts

This type of connectivity issue serves as a perfect example of how multiple layers in a network stack can affect real-world workflows. While it may seem like “Debian can’t connect to GitHub,” the underlying causes might range from expired SSL certificates to DNS misconfigurations or subtle problems with IPv6 routing.

The important part is to troubleshoot methodically:

  1. Verify DNS.
  2. Check SSL certificates.
  3. Test with other tools.
  4. Inspect firewall or proxy settings.
  5. Try alternate connection modes like SSH.

Being aware of these potential issues and their fixes not only helps you solve the specific problem but also strengthens your overall Linux networking know-how.

Conclusion

When Debian can reach Google but not GitHub, it’s a red flag. But it’s also an opportunity—a real-time puzzle to hone your troubleshooting skills. From DNS tweaking to certificate updates and proxy configurations, a systematic approach will get you back on track. With the solutions covered here, you should be better equipped to conquer this issue and any other network riddle Linux throws your way.

Happy debugging!