Not true, the NAS\ CAS sends the authentication requests to ACS on behalf of the user. If the NAS\ CAS is DHCPing prior to authentication, then the config is wrong.
You can force the situation of authentication then DHCP, by making the ACS the dhcp server (ip pools). You need to enable authorisation on the NAS\ CAS otherwise it ignores the ACS suggestion of an IP address.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...