I have reenable the MAC/KEX on beta cluster but then:
```
fatal: no matching mac found:
client: hmac-sha1-96,hmac-sha1,hmac-md5-96,hmac-md5
server: hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com [preauth]
```
And Jenkins yields with:
```
[06/22/15 14:49:05] [SSH] Opening SSH connection to 10.68.16.150:22.
Key exchange was not finished, connection is closed.
ERROR: Unexpected error in launching a slave. This is probably a bug in Jenkins.
java.lang.IllegalStateException: Connection is not established!
at com.trilead.ssh2.Connection.getRemainingAuthMethods(Connection.java:1030)
at com.cloudbees.jenkins.plugins.sshcredentials.impl.TrileadSSHPublicKeyAuthenticator.getRemainingAuthMethods(TrileadSSHPublicKeyAuthenticator.java:88)
at com.cloudbees.jenkins.plugins.sshcredentials.impl.TrileadSSHPublicKeyAuthenticator.canAuthenticate(TrileadSSHPublicKeyAuthenticator.java:80)
at com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.newInstance(SSHAuthenticator.java:207)
at com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.newInstance(SSHAuthenticator.java:169)
at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1173)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:701)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:696)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
[06/22/15 14:49:06] Launch failed - cleaning up connection
[06/22/15 14:49:06] [SSH] Connection closed.
```
We had the same issue with libjsch T100517 which has been backported T103342
On the Jenkins slaves we should have in sshd_config:
```
KexAlgorithms diffie-hellman-group-exchange-sha256
MACs hmac-sha2-512,hmac-sha2-256
```