I do not usually recommend using how-to documents found on the Internet.
Do not use the ifstated.conf script found here unless you understand the purpose of every single line in it. Never blindly copy and paste without knowledge. Questions about this script should be referred to the author, not here.
With that disclaimer, you may find this helpful.
http://www.chrisk.de/blog/2011/03/ho...er-on-openbsd/