Skip transport or network layer

[CISSP_Candidate]

AIO page 674 says SKIP works at network layer, Prep Guide Gold page 117 says SKIP works at transport layer, which one is correct?

[Jescoi]

These things become rather messy:
See http://www.sun.com/smi/Press/sunflash/1996-05/sunflash.960523.22946.xml where the statement is made "SKIP is a sessionless, key management protocol used at the network (Internet Protocol or IP) layer. "

However at http://www.networksorcery.com/enp/topic/ipsuite.htm, you will see SKIP described as a TRANSPORT layer protocol.

Personal opinion -- network.
Going out on a limb, SKIP, IKE, etc, are techniques that could be used theoretically at any layer by a protocol to provide keying materials for encrypted communication so it really doesn't make a lot of sense to talk about them in isolation as belonging to any layer. AIO is asserting that SKIP could be used by IPSec (which is a network level protocol) as an alternative to IKE.
-- Other folks have thoughts?