1. Cisco’s Secure Access Control Server (ACS)
ACS: Cisco’s AAA server
A centralized access control solution
Supports both RADIUS and TACACS+
Supports Cisco’s Network Access Control (NAC, aka Network Admission Control)

2. Network Access Control
Source:
AAA clients: aka NAD (network access devices), NAS (network access servers)
Posture validation/assessment: whether a host complies to security policies (e.g., antivirus s/w version & patches)
In a NAC deployment, the host that is running the Cisco Trust Agent (CTA) application collects posture data from the computer and from any NAC-compliant applications that are installed on the computer.
T. A. Yang
Network Security

3. ACS
Extensive support for common authentication protocols for end users/devices:
Passwords
PAP
CHAP
ARAP
MS-CHAP
LEAP
EAP-MD5
EAP-TLS
PEAP
T. A. Yang
Network Security

4. Shared Profile Components (SPC)
A shared profile is a set of authorization components that may be applied to one or more users or groups of users, and referenced by name within their profiles.
Benefits: scalability (by avoiding repetitions in configuring long lists of devices for commands and other authorization parameters)
e.g.,
Downloadable IP ACLs
Network access filters (NAF)
RADIUS authorization components (RAC)
Shell command authorization sets …
T. A. Yang
Network Security

5. Downloadable IP ACLs
A predefined and named set of ACL definitions (aka ACL contents) that can be associated to each applicable user or group of users by referencing its name
No need to repetitively define the same ACLs for each of the users and groups of users
RADIUS authentication is required for this feature to work with a client.
T. A. Yang
Network Security

6. Downloadable IP ACLs operate this way
Source:
When ACS grants a user access to the network, ACS determines whether a downloadable IP ACL is assigned to that user or the user's group.
If ACS locates a downloadable IP ACL that is assigned to the user or the user's group, it determines whether an ACL content entry is associated with the AAA client that sent the RADIUS authentication request.
ACS sends, as part of the user session, RADIUS access-accept packet an attribute specifying the named ACL and the version of the named ACL.
If the AAA client responds that it does not have the current version of the ACL in its cache (that is, the ACL is new or has changed), ACS sends the ACL (new or updated) to the device.
T. A. Yang
Network Security

7. Network access filters (NAF)
Source:
a named group of any combination of one or more of the following network elements: IP addresses, AAA clients (network devices), Network device groups (NDGs)
You can add a NAF that contains any combination of NDG, network devices (AAA clients), or IP addresses.
Benefits:
Defining a NAF saves you the effort of listing each AAA client explicitly.
Network devices (e.g., all NAC-L3-IP devices or all NAC-L2-IP devices) can be included in a single NAF for easy reference and application of authentication functions.
T. A. Yang
Network Security

8. Discussions
Bahiji
p.294: “Before NAF, per-device access restriction was not an option. … With NAF, granular application of access restrictions and downloadable ACLs is now possible, …”
p.293: “NAF regulates the access control on the basis of a AAA client’s IP address. Hence, ACLs can be uniquely tailored on a per-user, per-device basis.”
Q: Do you agree with the author that per-device access restriction is the primary benefit of using NAF?
T. A. Yang
Network Security

9. RADIUS authorization components (RAC)
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Network Security

10. Shell command authorization sets
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Network Security

11. Network access restrictions (NAR)
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Network Security

12. Machine access restrictions (MAR)
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Network Security

13. Network access profiles (NAP)
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Network Security

14. Support for NAC (Network Access Control)
Goal of NAC: A self-defending network (meaning?)
In addition to verifying the user identity, the NAS also validates the user computer’s posture.
Two implementation options:
Cisco NAC Appliance Solution (Cisco package)
Cisco NAC Framework (with 3rd party products)
More later …
T. A. Yang
Network Security

15. ACS support for Multifactor Authentication
Two or more factor authentication is desirable (and more secure).
ACS supports two-factor authentication:
ASCII
Password Authentication Protocol (PAP)
Protected Extensible Authentication Protocol (PEAP)
Extensible Authentication Protocol Generic Token Card (EAP-GTC), using token servers ?
T. A. Yang
Network Security

16. Vulnerability with Static Passwords
Static passwords are used over a period of time
Subject to brute force attacks and dictionary attacks
Eavesdropping attack
Replayed passwords
Q: Would encryption help?
Solution: Continually change the passwords  One-time passwords (OTP)
T. A. Yang
Network Security

17. One-Time Passwords
A different password is sent to the authentication server each time a user is authenticated.
A password is used one time only.
 A replayed password is useless.
Three mechanisms:
Math algorithm
Initial seed + hash(previous password)  next password
Challenge/Response
Prerequisite?
Time-synchronized
T. A. Yang
Network Security

18. Authentication Factors
What the user knows
What the user has
Smart cards, tokens (h/w or s/w)
What the user is
Biometric features
Where the user is
GPS based authentication
Combination of the above factors
T. A. Yang
Network Security

19. RSA SecureID A h/w or s/w token
Each token has a built-in random key (the seed)
time-synchronized OTP
Q: What are the two factors?
T. A. Yang
Network Security

20. ACS’s Support for Token Servers
ACS supports two types of token servers:
RADIUS token server
A token server with RADIUS i/f
ACS communicates with the token server using the RADIUS i/f.
Non-RADIUS token server
RSA SecureID token servers do not support the RADIUS protocol.
ACS uses RSA’s client s/w to communicate with the RSA token server.
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Network Security

21. Authentication using Token Servers
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Network Security

22. ACS’s Support for Token Servers
Cisco Secure ACS software supports authentication from these authentication servers:
CRYPTOCard
SecurID ACE/Server
SafeWord from Secure Computing
For each token server you plan to support, make sure you have properly installed the corresponding software before installing the Cisco Secure ACS. 
T. A. Yang
Network Security