How to fix 'mount.nfs: Connection timed out'

[Robert Rettig]

Hello i have setup a faiserver (install server) with debian jessie.
After several problems booting the demohost hangs on initramfs prompt
I tried to rebuild the nfsroot with

fai-make-nfsroot -k

it failed with:

ERROR: chroot /srv/fai/nfsroot aptitude -R -y -o
Dpkg::Options::=--force-confdef -o Dpkg::Options::=--force-confnew install
sysvinit-core nfs-common fai-nfsroot module-init-tools ssh rdate lshw
rpcbind rsync lftp less dump reiserfsprogs
e2fsprogs usbutils hwinfo psmisc pciutils hdparm smartmontools parted mdadm
lvm2 dnsutils ntpdate dosfstools xfsprogs xfsdump btrfs-tools procinfo
numactl dialog console-common kbd iproute moreutils udev subversion xz-utils
cupt pxelinux
 syslinux-common firmware-bnx2 firmware-bnx2x firmware-realtek
dracut-network live-boot- initramfs-tools- grub-pc linux-image-amd64 return
code 255
1 errors during executing of commands

executing the chroot command manually succeed and the demohost ist booting
but hangs now at another point


mount.nfs: Connection timed out

http://screencast.com/t/SsA2hn2Z 
after some time dracut is running wild searching for btrfs devices
http://screencast.com/t/7hdoVDVo 
and now shows a dracut prompt
http://screencast.com/t/NicMSyLyd
manually mounting the nfsroot on the demohost works
http://screencast.com/t/lFsJi91ywYx9

how can I fix the problem that dracut cannot mount my nfsroot?