NFS mounts and its propagation

[Sreeram B S <sreeramb@netapp.com>]

Hi,
     I am Sreeram. This question is related to NFS.
     I have a typical scenario. Please assume that there are 3 machines 
M1, M2, M3. Each of them are having directories /tmp/abc in them. All 
the NFS permissions are set appropriately.
     Now, a user mounts M2's /tmp/abc on M1's /tmp/abc by issuing mount 
command on M1. Mount is successful.
     Then the user mounts M3's /tmp/abc on M2's /tmp/abc by issuing 
mount command on M2. Mount successful.
     Now I would expect the contents of M3's /tmp/abc to be shown as 
output of 'ls' issue on M1. But this is not happening. I am unable to 
comprehend the reason. Could you please guide me?

     According to me, the contents of M3 should have shown up in M1's 
'ls' command,  because the /tmp/abc of M1 is nothing  but a *live* 
reflection of /tmp/abc of M2. So whatever changes are done to M2's 
/tmp/abc should be reflected on M1. Here, M2's /tmp/abc is mounting M3's 
/tmp/abc and so this change should be reflected on M1's /tmp/abc as 
well. But this isn't happening.

Kindly suggest if I am incorrect in my understanding or usage.
   The command I am using is:

    On M1:  mount -t nfs M2:/tmp/abc /tmp/abc
    On M2:  mount -t nfs M3:/tmp/abc /tmp/abc

Regards,
Sreeram