IP address in server_name

Hi there - is it possible to have a virtual host identified by IP
address as well as a default virtual host?

listen 22.22.22.22;
server_name 22.22.22.22;

http://22.22.22.22/

I have another server block with

server_name _;

defined, and this seems to be taking precedence - is that expected?
How can I get round it if so?

Thanks,
Igor