When you encounter the kex_exchange_identification: Connection closed by remote host error while trying to clone a GitHub repository or test your SSH connection, it typically indicates a network-level communication failure between your machine and GitHub's servers.

Before diving deep, let's verify some basic things:

# First, check if you're behind a firewall or proxy
ping github.com
traceroute github.com

# Verify your SSH configuration
cat ~/.ssh/config

1. Test GitHub Connectivity

Run this command to check if GitHub is reachable:

ssh -T git@github.com -v

The -v flag will give you verbose output to see where exactly the connection fails.

2. Check for Network Restrictions

Many corporate networks or countries block standard SSH port 22. Try connecting to GitHub's alternative SSH port:

ssh -T -p 443 git@ssh.github.com

3. Update SSH Configuration

Add these lines to your ~/.ssh/config file:

Host github.com
    Hostname ssh.github.com
    Port 443
    User git

Firewall and Antivirus Conflicts

Temporarily disable any firewall or antivirus software and test again. Some common offenders include:

• Windows Defender Firewall
• McAfee
• Norton
• Corporate network security policies

SSH Key Verification

Ensure your SSH keys are properly set up:

# Generate new SSH keys if needed
ssh-keygen -t ed25519 -C "your_email@example.com"

# Add key to SSH agent
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

# Copy public key to clipboard (Windows)
cat ~/.ssh/id_ed25519.pub | clip.exe

If SSH continues to fail, consider these alternatives:

# Use HTTPS instead
git clone https://github.com/username/repo.git

# Configure Git to store credentials
git config --global credential.helper store

After making changes, test your setup:

ssh -T git@github.com
# Should return: Hi username! You've successfully authenticated...

If you still face issues, check GitHub's status page (https://www.githubstatus.com/) for any ongoing outages.

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When you encounter the kex_exchange_identification error while trying to connect to GitHub via SSH, it typically indicates a network-level communication problem between your machine and GitHub's servers. The error occurs during the initial key exchange phase of the SSH handshake.

Several factors can trigger this error:

• Network connectivity issues (especially on corporate networks or VPNs)
• SSH port 22 being blocked by your firewall or ISP
• GitHub rate limiting due to multiple connection attempts
• Outdated SSH client configuration
• Problems with your SSH keys

First, verify basic connectivity to GitHub:

ping github.com
telnet github.com 22

If these fail, you likely have network connectivity issues. Try these diagnostic commands:

ssh -vT git@github.com  # Verbose mode for debugging
ssh -T -p 443 git@github.com  # Try alternate port

As a temporary workaround, switch to HTTPS:

git clone https://github.com/EmilYoung2004/git_test.git

Edit your SSH config file (~/.ssh/config) with these settings:

Host github.com
    Hostname ssh.github.com
    Port 443
    User git
    PreferredAuthentications publickey
    IdentityFile ~/.ssh/id_rsa

Check if your SSH keys are properly configured:

ls -al ~/.ssh  # Check existing keys
ssh-keygen -t ed25519 -C "your_email@example.com"  # Generate new key
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

For persistent issues, packet capture can reveal network-level problems:

sudo tcpdump -i any -w github_ssh.pcap port 22 and host github.com
# Analyze with Wireshark later

If you're still facing issues after trying these solutions:

1. Try from a different network (mobile hotspot works well)
2. Check GitHub status at status.github.com
3. Contact your network administrator about port 22 restrictions