Resolving Unable to SSH to Host Error - exception.host.ssh.connection.failed (KBA7955)

Applicable Delphix Versions

Click here to view the versions of the Delphix engine to which this article applies

Major Release	All Sub Releases
5.3	5.3.0.0, 5.3.0.1, 5.3.0.2, 5.3.0.3, 5.3.1.0, 5.3.1.1, 5.3.1.2, 5.3.2.0, 5.3.3.0, 5.3.3.1, 5.3.4.0, 5.3.5.0, 5.3.6.0, 5.3.7.0, 5.3.7.1, 5.3.8.0, 5.3.8.1, 5.3.9.0
5.2	5.2.2.0, 5.2.2.1, 5.2.3.0, 5.2.4.0, 5.2.5.0, 5.2.5.1, 5.2.6.0, 5.2.6.1

Issue

When trying to add a new environment or refresh an existing environment, the action fails with an error like the following:

Error: Unable to SSH to host "snoopy.acme.com".
Error Code: exception.host.ssh.connection.failed
Suggested Action: Make sure "snoopy.acme.com" is running and is reachable via SSH from the Delphix Engine.
Diagnosing Information: Reached a server listening on port 22 on host "snoopy.acme.com" from the Delphix Engine. 

This error generally happens on Delphix versions prior to 6.x when trying to add new or refresh existing environments because the Linux host does not allow SHA1 (Secure Hash Algorithm 1). Recent versions of Linux have deprecated SHA1 and removed support for it from the "sshd_config" file.

Troubleshooting Unable to SSH to Host Due to "Cannot negotiate, proposals do not match" Error

On some versions of Linux, it may be possible to review the /etc/ssh/sshd_config file to see which algorithms are supported. On others, you may need to run the following command as the root user to get a listing of the supported ciphers, key exchanges, and MACs:

# sshd -T | grep "\(ciphers\|macs\|kexalgorithms\)"
gssapikexalgorithms gss-gex-sha1-,gss-group14-sha1-
ciphers chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
macs umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
kexalgorithms curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1

Note:

Do not rely on the Delphix Engine ssh CLI connectivity test. It will succeed because partial support for SHA2 was added to Delphix 5.3.6.0 through 5.3.9.0.