Excluding a specific IP from rewrite

Question

I have an iframe that directs to an IP address like so

<iframe src="12.34.56.78:1234/index.html">

but my .htaccess rewrite rule redirects this ip back to my webserver, so I get an infinite loop of my own server.

How do I exclude a specific IP address from the rewrite rule? Here's my .htaccess file:

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^.*$ /index.php [L,QSA]