When dealing with IPSec based VPNs, I understand that there is a slight "problem" with symmetric key exchange. Obviously, you can't send the keys over the VPN, since they are used to guarantee the confidentiality of the information also sent over the VPN. So you have to use some sort of alternative route.
Now, I know that IPSec contains a process for this, IKE. But, would IKE work within a VPN? I found an interesting article on this, but right when it gets to a point where my current question would be answered, it seems to abruptly back off and leave me assuming that some common algorithms like DES, AES, Blowfish, RC4, etc., are used, and the encrypted keys are just sent in the clear.
Here is this article: http://csrc.nist.gov/publications/nistpubs/800-77/sp800-77.pdf (section 2.2)
So, when it comes to symmetric key transfer on a VPN that uses IPSec, how are the keys sent?