Zookeeper ACL based on host error

I want to create an ACL in Zookeeper that is host based, this is what I am trying to do.

In zkCli -

>>> setAcl / host:example.com:crdw

But I am getting this error.

Acl is not valid : /

I can set the IP based ACL just fine, so it >>> setAcl / ip:10.10.10.10:crdw

works.

What am I doing wrong with host based ACL?