can you please tell me, how nfs do a lookup for a client name? I have
a nfs share which is rw for client "iron". The client itself has two
interfaces with two IPs and DNS names ("iron" and "silver"). When I
try to mount the NFS Filesystem, I get sometimes a "permission denied"

I wouldn't change the rw permission to "iron and silver" because iron
is a virtual interface in a Cluster and is not bound to be on the
client silver. So maybe the IP iron belongs tomorrow to the cleint
"gold". In this case silver shouldn't be able to access the NFS share.

How can I force the NFS Client to mount the filesystem on a specified
interface so that it is mounted on the client iron everytime.