Ubuntu Full Disk Encryption on Hetzner Cloud – Adding Static Route in Initramfs

dropbearhetznerinitramfsstatic-routesUbuntu

I try to setup Ubuntu with full disc encryption on top of Hetzner Cloud. I got everything to work except the network connection in initramfs. Thanks to the UI console its possible to unlock, but I need SSH (dropbear) in init. I successfully using the same configuration on their root servers without any issues.

If I setup dropbear to get the IP by dhcp always resulting in NETWORK IS UNREACHABLE. But it gets the right parameters from the dhcp server. I asked Hetzner Support. They told me they think the dhcp client does not support RFC 3442 Classless Static Routes Option and recommended to add a static route with ip r a 172.31.1.1 dev ens3. Like on this Question I added the route, but always got the same error: NETWORK IS UNREACHABLE. I tested to set the route in different scripts, but nothing changed. I tested Ubuntu 16.04 and 18.04.

I'am happy about any recommends about this.
Thanks!

Best Answer

For those who come across this thread:

At least in Debian Stretch a little more generic configuration (which won't break on package update) works. We just configure network statically with a script in init-premount:

vi /etc/initramfs-tools/scripts/init-premount/static-routes

#!/bin/sh 
# /etc/initramfs-tools/scripts/init-premount/static-routes

# to avoid race condition
# we have to wait until the automatic network configuration via dhcp
# is finished
sleep 15

ip a add 192.168.0.18/32 dev eth0
ip route add 192.168.178.1 dev eth0
ip route add default via 192.168.178.1 dev eth0

exit 0

chmod 755 /etc/initramfs-tools/scripts/init-premount/static-routes

Related Solutions

Static route in initramfs

Create a little helper script that configures your static routing. According to the initramfs-tools manual scripts in /etc/initramfs-tools/scripts/nfs-premount are executed after the network interface has been enabled, but you may need to place the script in another sub directory.

You'll need to use ip route syntax because AFAIK the older route command won't be available:

#!/bin/sh 
# /etc/initramfs-tools/scripts/nfs-premount/static-routes

ip route add default via 172.31.1.1 dev ens3 

exit 0

and ensure that the script is executable (chmod 755 /etc/initramfs-tools/scripts/nfs-premount/static-routes) before running update-initramfs.

Netplan – Adding Static IP with Netplan on Ubuntu 18.04

In the end, I figured it out. Configure one interface to have two IP addresses:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: yes
      addresses: [$STATIC_IP/32]

then add an iproute table:

echo "mytable >> /etc/iproute2/rt_tables

add a rule:

ip rule add from all lookup mytable

add a route to the table:

ip route add default via $DHCP_GATEWAY src $STATIC_IP table mytable

Perhaps somebody will find that useful.

Best Answer

Related Solutions

Static route in initramfs

Netplan – Adding Static IP with Netplan on Ubuntu 18.04

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