The error "Couldn't agree a host key algorithm (available rsa-sha2-256, rsa-sha2-512)" typically occurs during an SSH connection attempt when the client and server cannot agree on a mutually supported host key algorithm.
In this case, the server only supports rsa-sha2-256 and rsa-sha2-512, but the client either does not support these algorithms or is configured to use different ones.A fix from Artica was added starting Artica v4.50 Service Pack 5 or Artica v4.50 Service Pack 4 Hotfix 20250714-17
The SSH client (e.g., OpenSSH, PuTTY, or another tool) may not be configured to support these algorithms or is using an older version that defaults to deprecated algorithms like ssh-rsa (which uses SHA-1 and is often disabled in modern SSH implementations for security reasons).
Update your SSH client and ensure your SSH client supports modern algorithms
¶ How to fix on Artica side without need to upgrade the client ?
- The fix is to add legacy support (not recommended long-term)
- You need to add
ssh-rsaand/orssh-dsson the Artica SSH settings. - Go to your main SSH configuration and look the Host key algorithms and Public key algorithms
- On the Host Key algorithms and Public key algorithms, click on “SSH-DSS” or “SSH-RSA”
