The good people of the Internet have taken care of that, copying all the versions to a number of "mirror" sites. This means that it is much faster to download a page. Unfortunately, this makes it much harder to search for items in the RFCs. If you are looking for all the RFCs that have a word in them, you will find all versions of all the RFCs. You might have to wade through a lot of different versions of other RFCs before you find the one you want.
The search box above will search all of ietf.org and only ietf.org. It will tell you what pages have the words or phrases you have. And, by clicking on Cached on the results page, you will quickly get Google's cached version instead of slowly get IETF's original version.