How do I fix: 🛑 Root Causes of the Error?

Insufficient or incompatible key exchange algorithms.Lack of support for certain SSH version or protocol versions.Firewall rules blocking the connection.

How do I fix: Method 2: Test Key Exchange Algorithms?

Step 1: Use the -o UserKnownHostsFile=/dev/null -o ServerKeyAlgorithms=ssh-rsa,ssh-dss,ecdsa-sha2-nsec,ecdsa-sha2-soft options when connecting to your SSH server.Step 2: If the connection is successful, it indicates that the key exchange algorithms are compatible. Otherwise, you may need to investig

Software⏱️ 2 min read📅 2026-05-31

How to Fix: What causes SSH error: kex_exchange_identification: Connection closed by remote host?

Q: How do I fix: 🔧 Proven Troubleshooting StepsMethod 1: Enable Default Key Exchange Algorithms?

Step 1: Open the SSH configuration file in a text editor and add the following line to enable default key exchange algorithms:DefaultUserKnownHostsFile /dev/nullDefaultHostKeyAlgorithms ssh-rsa,ssh-dss,ecdsa-sha2-nsec,ecdsa-sha2-softStep 2: Save and close the file. Restart the SSH service to apply t

Learn how to fix: What causes SSH error: kex_exchange_identification: Connection closed by remote host?.

Quick Answer: Try checking your system settings or restarting.

📋 Table of Contents

🛑 Root Causes of the Error
🔧 Proven Troubleshooting Steps
✨ Wrapping Up

The kex_exchange_identification: Connection closed by remote host error in SSH server logs can be caused by several factors, despite the server being publicly accessible and able to authenticate without issue. The most common cause of this error is related to the lack of key exchange algorithms supported by both the client and server.

🛑 Root Causes of the Error

Insufficient or incompatible key exchange algorithms.
Lack of support for certain SSH version or protocol versions.
Firewall rules blocking the connection.

🔧 Proven Troubleshooting Steps

Method 1: Enable Default Key Exchange Algorithms

Step 1: Open the SSH configuration file in a text editor and add the following line to enable default key exchange algorithms:
DefaultUserKnownHostsFile /dev/null
DefaultHostKeyAlgorithms ssh-rsa,ssh-dss,ecdsa-sha2-nsec,ecdsa-sha2-soft
Step 2: Save and close the file. Restart the SSH service to apply the changes.

Method 2: Test Key Exchange Algorithms

Step 1: Use the -o UserKnownHostsFile=/dev/null -o ServerKeyAlgorithms=ssh-rsa,ssh-dss,ecdsa-sha2-nsec,ecdsa-sha2-soft options when connecting to your SSH server.
Step 2: If the connection is successful, it indicates that the key exchange algorithms are compatible. Otherwise, you may need to investigate further.

✨ Wrapping Up

By implementing these steps and ensuring that the key exchange algorithms supported by both your SSH server and clients are compatible, you can resolve the kex_exchange_identification: Connection closed by remote host error.

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