Answer by Jacob Evans for nginx 302 redirect only naked IP

Put it in quotes and now it's as expected.

server {    listen 198.251.86.133:80;    server_name "198.251.86.133";    return 302 http://www.jacobdevans.com/anycast-301/;}server {    listen 198.251.86.133:80 default_server;    server_name _;    return 301 http://www.$host$request_uri;}