When specifying a range prefix withing a subnet in the dhcpv6-server config section, if the range is of the shape:
```
2001:aaa:bbb::ccc:/xxx
```
the VyOS configurator will accept the value but dhcpdv6 won't start and will error out on the range6 line.
This can be fixed by specifying the address as follows (i.e. by adding a trailing 0):
```
2001:aaa:bbb::ccc:0/xxx
```
Maybe VyOS should automatically add a 0 before putting the range in the dhcpdv6.conf file?