This router has no private options. Unless it is being used purely for verification (see verify_only) a transport is required to be defined by the generic transport option. The router accepts the address if its domain part takes the form of an RFC 2822 domain literal, that is, an IP address enclosed in square brackets. For example, this router handles the address
by setting up delivery to the host with that IP address. If an IP literal turns out to refer to the local host, the generic self option determines what happens. The RFCs require support for domain literals, though it seems anachronistic in today's Internet.
If you want to use this router, you must also set the main configuration option allow_domain_literals. Otherwise, Exim will not recognize the domain literal syntax in addresses.