dracut: "No carrier detected on interface eth0", but interface later gets up

Hello,

I'm sysadmin at a German highschool and want to install debian clients using fai.

I set up a client using
fai-chboot -Iv -f verbose,sshd,createvt,reboot -u nfs://faiserver/srv/fai/config 90:1B:0E:C5:4E:48

The client is booting fine, entering dracut. However, eth0 won't reach state UP. From rdsosreport.txt (see attachment):
...
+ '[' 49 -lt 50 ']'
+ '[' -n 1 ']'
++ ip -o link show up dev eth0
+ li='2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000    link/ether 90:1b:0e:c5:4e:48 brd ff:ff:ff:ff:ff:ff'
...

Thus, I get:
"No carrier detected on interface eth0"

After some time, dracut is dropping to debug shell.
However, from there, I can mount nfsroot as follows ("ip -o link show up dev eth0" now (i.e. after about 205 sec.) gives state "UP"):

dracut:/# dhclient eth0
dracut:/# mkdir -p /mnt/nfs
dracut:/# mount.nfs 172.16.7.152:/srv/fai/config /mnt/nfs

Thus, configuration seems to be fine, I guess.

I tried two different computer models, but on none I could get eth0 to state UP, however, I could mount nfs from debug shell.

My fai-server is in a kvm running only tftp-server. dhcp-server is on another machine, setting "next-server" and "filename" for pxe-client. But this should be irrelevant, I guess.

  From rdosreport.txt, I guess dracut version:
+ cat /lib/dracut/dracut-048+80-1-1-3-gebb7dd39
dracut-048+80-1-1-3-gebb7dd39

I am quite desperate now, "digitalisation" is knocking on the doors.
Can somebody please help?

Thanks, Markus