Your post implies but is not clear that traffic from the router and switches must go through the ASA5520 to get to ACS. Can you clarify that this is the case?
If there is an ASA in the path from router and switches to ACS, my first guess would be that ASA was not allowing the traffic. Can you tell us whether the router and switches are using TACACS or Radius to request authentication with ACS? And can you post the parts of the config of the ASA in which you open the ports?
There might be some other causes of this problem. Can you verify whether the router and switches have IP connectivity to the ACS? If you traceroute from the router and switches to the ACS does the traffic take the path that you expect?
Is it possible that there is some config error in the router and switches - is there possibly an incorrect server address or incorrect key?
If you run debug for authentication (TACACS or Radius, whichever you are using) and attempt to authenticate what is in the debug output?
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...