For routes to be installed into the kernel, the source IP must be bound to an interface. Often the CRXN address is not on any interface. Therefore one creates a dummy interface. Alternatively, you can bind the CRXN IP address to the loopback interface. If the CRXN IP address is not bound to an interface, the `Netlink: Invalid argument` error can occur at bird.
You can create a dummy interface with the following command:
```
ip link add crxn type dummy
ip link set dev crxn up
```
Here `crxn` is the name of the interface.
To bind the CRXN IP address to the interface you can use the following command:
```
ip addr add dev crxn <ip>/128
```
Replace `<ip>` with the CRXN IP address.
To delete the dummy interface you can use the following command:
```
ip link del crxn
```
## Automatic start with ifupdown
```
auto crxn
iface crxn inet6 manual
pre-up ip link add crxn type dummy
up ip addr add dev crxn <ip>/128
post-down ip link del crxn
```
Alternatively, you can use the following configuration: