Hi All,

There is scenario.
We have n number of servers (RHEL 5) having OpenSSH 4.2 version. Now I want to update OpenSSH to 5.2 or latest version on any new servers added in the cluster. Can any body describe if there will be any problem while communication between servers having OpenSSH 4.2 and OpenSSh 5.2 or more. I think there should not be a problem, Please suggest on this. Or wheather I should go and update all the server's OpenSSH to same version. If there is any challenge or problem let me know.
Waiting for reply from you all.

I say there would be no problem. But I think upgrading to 6.6 or newer would be wise.

So there would not be any problem (forward compatibility) while OpenSSH 4.2 communicates with OpenSSH latest version, obviously backward compatibility if there for sure. Any comparison or docs verifying above. So I can go for upgrading the new servers with OpenSSH 6.7 and old servers can communicate to these new servers without any problem.

openssh 6.7 removes some old protocols. You should see release notes and docs of both 4.2 and 6.7.

Another thing you should find which type of the key you are using in 4.2.

You can test between two systems then scale.

I run in an environment mixing several versions of OpenSSH (RHEL4, 5, 6, and Suse in the same data center with a wild mix of CentOS test machines) and have never had a communications problem due to version differences betwee the machines.