How to Fix ssh_exchange_identification read Connection reset by peer Error?

Secure Shell (SSH) is a protocol utilized for secure network communication, providing encrypted remote access to servers and computers across unsecured networks. Unlike protocols like Telnet and FTP that transmit data in plain text, SSH ensures confidentiality even over public networks like the internet, making it the de-facto standard for system administrators.

However, SSH connections can encounter various errors that require immediate attention. One common and frustrating error is the ssh_exchange_identification read Connection reset by peer error, which can prevent remote server access and command execution.

Understanding the Error

The ssh_exchange_identification read Connection reset by peer error occurs during the initial SSH connection setup. The ssh_exchange_identification refers to the process where both client and server exchange identification information during handshake.

The Connection reset by peer portion indicates that the server abruptly terminated the connection during the identification phase, without sending back any identifying information. This typically happens before the authentication process even begins.

Common Causes

Network Issues

Network connectivity problems are frequent culprits, including high traffic causing packet loss, network instability, or connecting through proxies/routers that block outgoing SSH traffic on port 22.

Firewall Restrictions

Firewalls blocking incoming SSH traffic on port 22 (or custom SSH ports) prevent connection establishment. Both client-side and server-side firewalls can cause this issue.

SSH Configuration Problems

Mismatched encryption algorithms between client and server, incorrect authentication credentials, IP address restrictions, or server configuration issues can trigger handshake failures resulting in this error.

Basic Troubleshooting Steps

1. Check Network Connectivity

First, verify basic connectivity between your client and the target server

ping target_server_ip
telnet target_server_ip 22

The ping command tests basic network reachability, while telnet verifies that port 22 is open and accepting connections.

2. Test with Verbose Mode

Enable SSH verbose output to gather detailed connection information

ssh -v username@target_server
ssh -vv username@target_server    # More verbose
ssh -vvv username@target_server   # Maximum verbosity

This reveals exactly where the connection fails and provides clues about the root cause.

3. Temporarily Disable Firewalls

Test connectivity with firewalls temporarily disabled on both client and server sides. On Linux servers

# Ubuntu/Debian
sudo ufw disable

# CentOS/RHEL
sudo systemctl stop firewalld

If the connection succeeds, configure firewall rules to allow SSH traffic on the appropriate port.

Advanced Solutions

Server-Side Configuration Fixes

Edit the SSH daemon configuration file /etc/ssh/sshd_config and implement these changes

# Disable reverse DNS lookups
UseDNS no

# Increase connection timeout
ClientAliveInterval 60
ClientAliveCountMax 3

# Allow specific users/IPs
AllowUsers username
AllowHosts 192.168.1.0/24

After making changes, restart the SSH service

sudo systemctl restart sshd

Client-Side Configuration

Create or modify the SSH client configuration in ~/.ssh/config

Host target_server
    HostName server_ip
    Port 22
    User username
    ConnectTimeout 30
    ServerAliveInterval 60

Alternative Port Testing

If the default port 22 is blocked, test alternative SSH ports

ssh -p 2222 username@target_server
ssh -p 443 username@target_server

Prevention Strategies

• Regular monitoring Monitor SSH logs in /var/log/auth.log for connection patterns and failed attempts.

• Network stability Ensure stable network infrastructure and consider SSH connection multiplexing for unreliable networks.

• Configuration management Use configuration management tools to maintain consistent SSH settings across servers.

• Security updates Keep SSH software updated to prevent compatibility issues and security vulnerabilities.

Conclusion

The ssh_exchange_identification read Connection reset by peer error typically stems from network connectivity issues, firewall restrictions, or SSH configuration problems. By systematically checking network connectivity, using verbose mode for detailed diagnostics, and adjusting both client and server configurations, this error can be resolved effectively. Regular monitoring and proper SSH configuration management help prevent future occurrences.