I'm not sure if this question belongs here or in the Networking forum. I'm sorry if its in the wrong forum.

After running rkhunter on a (CentOS 3.5) file server I responded to one of its complaints by dropping support for SSH V1. I was surprised next when the nfs connections to clients were all broken. I was unaware the NFS service relies on SSH. However,when I reinstated SSH V1 support the NFS connections came back up again. So apparently it does.

I was surprised because I thought NFS was a plain text protocol without any security. Could someone explain for me how NFS uses SSH?
Thanks

I've seen NFS tunneling through SSH, but I 'm not aware of any distros that use NFS encryption/tunneling by default. Could you explain in more detail the steps you took to disable SSH v1 support. Also, take a look at the output of ps aux and see how sshd is running (ps aux | grep sshd). With ssh tunneling you'll see it running with the port forwarding options.

Yes the steps I took were to stop SSH1 by removing protocol 1 from the line in /etc/ssh/sshd_config below
#Port 22
#Protocol 2,1
That seems to have been sufficient to break nfs

The output of ps aux | grep sshd (after restoring ssh1) is
[root@lance netadmin]# ps aux | grep sshd
root 1668 0.0 0.1 3664 516 ? S Oct02 0:00 /usr/sbin/sshd
root 5725 0.0 0.2 4244 772 pts/0 S 08:14 0:00 vi sshd_config
root 5800 0.0 0.2 3672 660 pts/2 S 08:18 0:00 grep sshd

Thanks

Per chance did you restart networking on the server without unmounting the NFS volumes on the clients first?