The `allow-update` block in `named.conf` enumerates the hosts/networks
that are allowed to issue dynamic DNS updates. This is required in
Active Directory and other environments where clients and/or DHCP
servers create DNS records automatically.
By default, the block is omitted from the generated configuration file.
The `named_allow_update` variable can be set to a list of patterns (e.g.
CIDR blocks, ACL names, etc.) to populate it.
The *named* role configures the BIND DNS server on managed nodes. It
writes `/etc/named.conf`, using a template that supports most of the
commonly-used options. The configuration can be augmented by other
templates, etc. by specifying file paths in the `named_options_include`
or `named_global_include` variables, both of which are lists.
Dustin