fibre problem with Intel 82571EB

[Frank Weißer <linux@weisser-ol.de>]

Hi folks!
Situation:
Debian-Edu 10 Server with

eth0 NC(=unused)
00:19.0 Ethernet controller: Intel Corporation 82566DM-2 Gigabit Network 
Connection (rev 02)
        Subsystem: Fujitsu Technology Solutions 82566DM-2 Gigabit 
Network Connection
        Kernel driver in use: e1000e

eth1-4
eth1 NC
eth2 NC
eth3 flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.254  netmask 255.255.255.0
eth4 flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.2.2  netmask 255.0.0.0
04:00.1 Ethernet controller: Intel Corporation 82571EB Gigabit Ethernet 
Controller (Fiber) (rev 06)
        Subsystem: Intel Corporation PRO/1000 PF Quad Port Server Adapter
        Kernel driver in use: e1000e

I can reach tjener via fibre cable and switch and use it with scp, smb 
and so on.
But dhcp, bxe-boot and ltsp-clients don't work.

dhcp requests via
#dhclient eth4
need about 70 seconds to give me an ip. Network manager already gives up 
in that time. Even connecting direct (with a media converter, not using 
other fiber cables or switches) doesn't work.
So cable/switch don't seam to hurt.

How can I tell 82571EB to do its work?

If I switch eth4's address to eth0 (copper) everything works fine. So 
services seem to be running

appreciating any answer

readu
Frank