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Cisco ASA Series Firewall ASDM Configuration Guide
Chapter 8 Configuring AAA Rules for Network Access
Configuring Authorization for Network Access
4. After receipt of a RADIUS authentication request that has a username attribute that includes the
name of a downloadable ACL, Cisco Secure ACS authenticates the request by checking the
Message-Authenticator attribute. If the Message-Authenticator attribute is missing or incorrect,
Cisco Secure ACS ignores the request. The presence of the Message-Authenticator attribute
prevents malicious use of a downloadable ACL name to gain unauthorized network access. The
Message-Authenticator attribute and its use are defined in RFC 2869, RADIUS Extensions,
available at http://www.ietf.org.
5. If the ACL required is less than approximately 4 KB in length, Cisco Secure ACS responds with an
access-accept message that includes the ACL. The largest ACL that can fit in a single access-accept
message is slightly less than 4 KB, because part of the message must be other required attributes.
Cisco Secure ACS sends the downloadable ACL in a cisco-av-pair RADIUS VSA. The ACL is
formatted as a series of attribute-value pairs that each include an ACE and are numbered serially:
ip:inacl#1=ACE-1
ip:inacl#2=ACE-2
.
.
.
ip:inacl#n=ACE-n
ip:inacl#1=permit tcp 10.1.0.0 255.0.0.0 10.0.0.0 255.0.0.0
6. If the ACL required is more than approximately 4 KB in length, Cisco Secure ACS responds with
an access-challenge message that includes a portion of the ACL, formatted as described previously,
and a State attribute (IETF RADIUS attribute 24), which includes control data used by Cisco Secure
ACS to track the progress of the download. Cisco Secure ACS fits as many complete attribute-value
pairs into the cisco-av-pair RADIUS VSA as it can without exceeding the maximum RADIUS
message size.
The ASA stores the portion of the ACL received and responds with another access-request message
that includes the same attributes as the first request for the downloadable ACL, plus a copy of the
State attribute received in the access-challenge message.
This process repeats until Cisco Secure ACS sends the last of the ACL in an access-accept message.
Configuring Cisco Secure ACS for Downloadable ACLs
You can configure downloadable ACLs on Cisco Secure ACS as a shared profile component and then
assign the ACL to a group or to an individual user.
The ACL definition consists of one or more ASA commands that are similar to the extended access-list
command (see command reference), except without the following prefix:
access-list acl_name extended
The following example is a downloadable ACL definition on Cisco Secure ACS version 3.3:
+--------------------------------------------+
| Shared profile Components |
| |
| Downloadable IP ACLs Content |
| |
| Name: acs_ten_acl |
| |
| ACL Definitions |
| |
| permit tcp any host 10.0.0.254 |
| permit udp any host 10.0.0.254 |
| permit icmp any host 10.0.0.254 |
| permit tcp any host 10.0.0.253 |