This song is essentially a 12-bar blues in the key of G, and it uses just three chords: G, C, and D. This is what we call the I, IV, and V in the key of G.
If you are not familiar with this, or the 12-bar blues at all for that matter, don’t worry. I’ve got a number of detailed lessons that can help you learn this in a step-by-step path. Check out the Essential Blues Guitar System HERE: https://www.jonmaclennan.com/essentialbluesguitarsystem
While the chords to "Further On Up The Road" are simple the groove is deep, and the solos that Clapton and Robertson play on top of this progression are world-class!
Have fun working on it in today's guitar lesson!