set interfaces dummy dum1 address 2001:db8::1/64
commit
set interfaces dummy dum1 address 2001:db8::1/32
commit

vyos@r14# commit
[ interfaces dummy dum1 ]
Traceback (most recent call last):
  File "/usr/libexec/vyos/services/vyos-configd", line 157, in run_script
    script.apply(c)
  File "/usr/libexec/vyos/conf_mode/interfaces_dummy.py", line 64, in apply
    d.update(dummy)
  File "/usr/lib/python3/dist-packages/vyos/ifconfig/interface.py", line 1839, in update
    self.add_addr(addr, vrf_changed=vrf_changed)
  File "/usr/lib/python3/dist-packages/vyos/ifconfig/interface.py", line 1299, in add_addr
    self._cmd(tmp)
  File "/usr/lib/python3/dist-packages/vyos/ifconfig/control.py", line 66, in _cmd
    return cmd(command, self.debug, env=env)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/vyos/utils/process.py", line 189, in cmd
    raise OSError(code, feedback)
FileNotFoundError: [Errno 2] failed to run command: None  ip addr add 2001:db8::1/32 dev dum1
returned: 
exit code: 2

[[interfaces dummy dum1]] failed
Commit failed
[edit]
vyos@r14# 
[edit]
vyos@r14# sudo ip addr add 2001:db8::1/32 dev dum1
Error: ipv6: address already assigned.
[edit]
vyos@r14#