NFS does not open port 2049

This seems to be a wrong assumption.
The clients do not need having port 2049 open.
The clients contact the server, so the server has to have an active port
Hopefully nobody tries to contact the clients, and they do not need the port for incoming nfs requests open (and for security purposes they shouldn't).

So what is the problem now as I have cleared the "authentication' problem. This eventually times out as there appears to be no route to host.

ea@azura:~$ sudo mount -v -t nfs -o proto=tcp,port=2049 192.168.0.12:/export/mass /media/mass
[sudo] password for ea:
mount.nfs: timeout set for Thu Jan 24 11:27:34 2019
mount.nfs: trying text-based options 'proto=tcp,port=2049,vers=4.2,addr=192.168.0.12,clientaddr=192.168.0.13'
mount.nfs: mount(2): No such file or directory
mount.nfs: trying text-based options 'proto=tcp,port=2049,addr=192.168.0.12'
mount.nfs: prog 100005, trying vers=3, prot=6
mount.nfs: trying 192.168.0.12 prog 100005 vers 3 prot TCP port 50209

mount.nfs: portmap query failed: RPC: Remote system error - No route to host

mount.nfs: trying text-based options 'proto=tcp,port=2049,vers=4.2,addr=192.168.0.12,clientaddr=192.168.0.13'

Do you have portmap and/or iptables running on the server?
If yes, are they correctly configured to allow nfs access from the clients?

I have yet to find portmap
I do have firewalld running and as far as I know all clients have access, as NFS service s set on port 2049 as well as zone is set to home with a listing of all IP's.
Similarly on the clients.

I now after some digging end up with stale file handles

I shall try to find out about portmap.

Just checked again and portmap is running and showing port 2049 available with tcp

What are the contents of hosts.allow and hosts.deny?

cat /etc/hosts.deny
cat /etc/hosts.allow

ea@discovery:~$ cat /etc/hosts.allow
# /etc/hosts.allow: list of hosts that are allowed to access the system.
# See the manual pages hosts_access(5) and hosts_options(5).
#
# Example: ALL: LOCAL @some_netgroup
# ALL: .foobar.edu EXCEPT terminalserver.foobar.edu
#
# If you're going to protect the portmapper use the name "rpcbind" for the
# daemon name. See rpcbind(8) and rpc.mountd(8) for further information.
# next line added for NFS usage
#rcpbind mountd nfsd statd lockd rquotad :
 127.0.0.1 192.168.0.11 192.168.0.12 192.168.0.13 192.168.0.10

ea@discovery:~$ cat /etc/hosts.deny
# /etc/hosts.deny: list of hosts that are _not_ allowed to access the system.
# See the manual pages hosts_access(5) and hosts_options(5).
#
# Example: ALL: some.host.name, .some.domain
# ALL EXCEPT in.fingerd: other.host.name, .other.domain
#
# If you're going to protect the portmapper use the name "rpcbind" for the
# daemon name. See rpcbind(8) and rpc.mountd(8) for further information.
#
# The PARANOID wildcard matches any host whose name does not match its
# address.
#
# You may wish to enable this to ensure any programs that don't
# validate looked up hostnames still leave understandable logs. In past
# versions of Debian this has been the default.
ALL:PARANOID

ea@discovery:~$
  I also discovered there were no iptables rules on discovery (the server) , so I entered rules :

sudo iptables -A INPUT -s 192.168.0.10 -j ACCEPT

for all four comouters and saved them by entering : sudo /sbin/iptables-save

also : sudo iptables INPUT -p tcp -m tcp --dport 2049 -j ACCEPT

  I also make quite a few typing errors, the contents of /sbin/iptables-save
:
ea@discovery:~$ sudo iptables -L line-numbers
[sudo] password for ea:
iptables: No chain/target/match by that name.
ea@discovery:~$ sudo iptables -L --line-numbers
Chain INPUT (policy ACCEPT)
num target prot opt source destination
1 ACCEPT all -- vostro.hitronhub.home anywhere
2 ACCEPT all -- seanix.hitronhub.home anywhere
3 ACCEPT all -- discovery.hitronhub.home anywhere
4 ACCEPT all -- azura.hitronhub.home anywhere
5 tcp -- anywhere anywhere tcp dpt:nfs

Chain FORWARD (policy ACCEPT)
num target prot opt source destination

Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
1 ACCEPT all -- discovery.hitronhub.home anywhere
2 tcp -- anywhere anywhere tcp dpt:nfs
ea@discovery:~$

I assume that the contents of you /etc/hosts.allow are wrong with the consequence that they block ALL access from the clients to the server.

If the syntax is correct, then the IP's are also correct.

I have a new modem/router which assigned the new IP's as 192.168.0.10 etc to 13
My old D-Link modem had IP's from 192.168.0.101 through 106

I started reading a new document about NFS4: "NFSv4 Enjancements and Best Practices Guide"

It shows a lot of differences between nfs3 and 4, some of which might be part of my problem.

I shall study it in detail and see what specifically applies to my setup.

In my opinion the syntax in /etc/host.allow is wrong.
It needs pairs
daemon_list : client_list
I cannot see this in your file.

see http://manpages.ubuntu.com/manpages/bionic/en/man5/hosts.allow.5.html

Of course my problem is not solved, I will study the hosts.allow document as well as the NFSv4 document and then formulate a plan that will make NFS4 work for me.

I will report on that in a new thread.

Why are you spreading the information over several different question?
You make life for the supporters harder than necessary.

We have spent most of this month on this and I am just about ready to give up, go back to NFSv3 and get things working without the troubles I have now caused... If all of the questions and answers were in one document, it would be very difficult to read it all and to make any sense out of it.

I sincerely thank you for your help and suggestions, I do appreciate it.

Reading the NFSv4 Enhancements and Best Practices guide tells me to stop trying to fix this and that and to start fresh making a plan of attack first.