Why "of course" ?
Applying what you explained above, this would mean that my images paths will
be resolved as:
http://172.18.0.1/SEDO/image.gif
Which of course will not work.
I may be thick, but I must admit I do not really understand your problem.
What I mean is : if the page your browser sees contains a tag <img href="" the browser will resolve this according to the location from which it got the page that contains that link.
That's how browsers work, and are supposed to work.
If you do not want this, then do not put relative links in the pages, put absolute links.
Like <img href=""> The browser, mind you, will still resolve this according to the host from which it got your page, but this time will look for http://172.18.0.1/images/image.gif.
But what do you want to happen, really ?
Where would you like the image to come from ?