Internalists maintain that what qualifies a belief as knowledge is another belief, or perhaps another internal mental state. When asked why you believe something, you have to say "Because..." and give another belief or beliefs that provide(s) sufficient grounds for it. "Why do you believe Socrates is mortal?" "Well, because I believe all men are mortal, and because I believe Socrates is a man." Externalists maintain that what qualifies a belief as knowledge are the factors, external to the mind, that the belief is about. I believe there is a tree in front of me; if the reason I believe there is a tree in front of me is because there is a tree in front of me, then my belief has the status of knowledge. (There are internalist-externalist debates elsewhere in philosophy as well; in philosophy of mind, philosophy of language, etc.) This leaves a lot out of course. The shorthand version is whether one has to know that he knows something in order to know it. Internalists say yes, externalists say no, and Plantinga says ... sometimes.
So there isn't anything at all like a simple, single answer to the question whether warrant for grounded beliefs requires that the subject know that the ground is an indicator of the belief; sometimes this is required and sometimes it is not. And the reason is not far to seek. In some cases it is perfectly in accord with proper cognitive function to believe A on the basis of B even if you have never had any views at all as to whether B is an indicator of A; in a wide variety of other cases a properly functioning human being will believe A on the basis of B only if she has first learned that B reliably indicates A.
That's from page 44 of Warrant and Proper Function (sixth paragraph from the end here). Now I agree with Plantinga on this. Sometimes you do need to have this second-order knowledge in order to have the first-order knowledge, and sometimes you don't. He seems to be suggesting that these cases can't be systematized; on that point I'm not as pessimistic as him, but it wouldn't really surprise me if they couldn't. Regardless, once you concede that you sometimes need to know that something is a reliable indicator of something else before you can have knowledge of the something else, you're no longer a pure externalist. Perhaps you're something more along the lines of an Alstonian internalist-externalist, I don't know.
Now in the previous post I claimed that Plantinga's EAAN is essentially a global skeptical argument that arises from within externalist and naturalized epistemology. Does the fact (or my claim at least) that Plantinga's epistemology is not purely externalist change that? I don't see how my qualification of Plantinga's externalism has any point of contact with his EAAN. And even if it did, it could easily be weeded out. I explained how Plantinga's argument fits into externalist epistemologies in the previous post, so I would just refer you there. Plantinga, it should be noted, has written elsewhere that his argument does not presuppose any particular epistemological framework, but as you can guess, I disagree with him on that too.