ok then change 192.168.1.1 to 192.168.1.5 in /etc/exports and restart nfs

When I try to connect via IP, Ubuntu says "internal error".

see what /var/log/messages has to say ?

The log says nohing about NFS. :S

I have a idea.

If you tell me what information I need to come up with, so please tell me exactly what I need to do to get it to work.
It is a little easier now that I'm not so good for Linux yet.

ok, so far you have setup an ip which is 192.168.1.5 binded to your server, you have got nfs server running on it, what we need to do right now is to check whether we have setup nfs correctly or not to check that try the following on your server,
mount -t nfs 192.168.1.5:/home/nicolas/Musiknumre /nfstesting

where /nfstesting is your mount point, also make sure portmap rpc services are running.

Now my Export-file look like this:

# /etc/exports: the access control list for filesystems which may be exported
# to NFS clients. See exports(5).
#
# Example for NFSv2 and NFSv3:
# /srv/homes nicolas-desktop(rw,sync) nicolas-laptop(rw,sync)
#
# Example for NFSv4:
# /srv/nfs4 gss/krb5i(rw,sync,fsid=0,crossmnt)
# /srv/nfs4/homes gss/krb5i(rw,sync)
#
/home/nicolas/Musiknumre 192.168.1.5 (rw,sync)
________________________

When i try "Sudo mount -t nfs 192.168.1.5:/home/nicolas/Musiknumre /nfstesting", it works!
What did it work?

And how do I unmount the harddrive again?

I find out how i unmount.

Now I just missing something knowledge of /etc/hosts.allow and /etc/hosts.deny. a website says that without making use of them, NFS is not safe.

What needs to be in them?

i have no idea about how to prevent or allow them from mounting using tcpwrappers.

Ok. But thank you very much for you big help!

There are different ways your nfs server could be running. An xinetd service, as a normal service or using the nfs kernel support. If it is an xinetd service you can either use /etc/hosts.allow, /etc/hosts.deny or use /etc/xinetd.d/nfs to configure access.

If /etc/xinetd.d/nfs exists, you can add an "only_from" entry. This entry could be like "10.1.1.10,12,15" to allow only 10.1.1.10, 10.1.1.12 and 10.1.1.15 access. If you have a small number of client hosts, you could use iptables rules that allow access from just certain hosts and by default drop nfs requests from other hosts. The requests will be either dropped or denied in this case.

To prevent IP spoofing by other hosts on the LAN, you could add MAC address entries to arp.

sudo /sbin/arp -s <ip address> <mac address>

Of course, a user could manually change the MAC and IP address on their host. To totally prevent that, you need to use authentication. If your switch is configurable, then you may be able to configure it to only allow traffic on that port from a particular MAC address. This could provide general arp spoofing protection for your network.