NFS versus the firewall

[Tim]

Something has bugged me for ages about trying to use NFS between
machines on the LAN.  I've still got a central server running FC4,
because everything (FC 5 through to 7) can make use of it.  But none of
the other OSs can do machine to machine NFS to each other (not FC5 to
FC5, FC6 to FC6, nor FC7 to FC7), even though I've ticked the
system-config-securitylevel box to allow NFS through the firewall, I
have to disable the firewall to do it.

Why does it give an NFS option if it doesn't work?  All the other
service tick boxes work (if I tick WWW, I can webserve without any
firewall issues, etc.).  Surely, given a firewall configurator with
preset options, all that two FC7 users need to do to NFS between each
other is to tick the NFS option?  It seems extraordinarily badly
designed if it doesn't.

Yes, I have allowed NFS options in the SELinux configurator, as well.
And, no, I do NOT want to use Samba.

Any box can use the auto networking thingo where something like
less /net/server/home/tim/testfile automatically works.  But try
accessing any of the newer than FC4 boxes, and it doesn't.

e.g. [tim at suspishus ~]$ ls /net/bigblack/home/tim/
     ls: cannot access /net/bigblack/home/tim/: No such file or directory

With "bigblack" being the hostname of a FC7 box on the LAN.  And, yes,
the name resolves.  I have fully functioning local DNS, in both forward
and reverse directions.

-- 
(This computer runs FC7, my others run FC4, FC5 & FC6, in case that's
 important to the thread.)

Don't send private replies to my address, the mailbox is ignored.
I read messages from the public lists.