In the Cisco TrustSec solution, security group access transforms a topology-aware network into a role-based network, thus enabling end-to-end policies enforced on the basis of role-based access-control (RBAC). Device and user credentials acquired during authentication are used to classify packets by security groups. Every packet entering the Cisco TrustSec cloud is tagged with a security group tag (SGT). The tagging helps trusted intermediaries identify the source identity of the packet and enforce security policies along the data path.

An SGT can indicate a privilege level across the domain when the SGT is used to define a security group ACL. An SGT is assigned to a device through IEEE 802.1X authentication, web authentication, or MAC authentication bypass (MAB), which occurs with a RADIUS vendor-specific attribute. An SGT can be assigned statically to a particular IP address or to a switch interface. An SGT is passed along dynamically to a switch or access point after successful authentication.

The Security-group eXchange Protocol (SXP) is a protocol developed for Cisco TrustSec to propagate the IP-to-SGT mapping database across network devices that do not have SGT-capable hardware support to hardware that supports SGTs and security group ACLs. SXP, a control plane protocol, passes IP-SGT mappings from authentication points (such as legacy access layer switches) to upstream devices in the network.

The SXP connections are point-to-point and use TCP as the underlying transport protocol. SXP uses the well known TCP port number 64999 to initiate a connection. Additionally, an SXP connection is uniquely identified by the source and destination IP addresses.

To provide identity and policy-based access enforcement, the Cisco TrustSec solution includes the functionality:

• Access Requestor (AR): Access requestors are end-point devices that request access to protected resources in the network. They are primary subjects of the architecture and their access privilege depends on their Identity credentials.

Access requestors include end-point devices such PCs, laptops, mobile phones, printers, cameras, and MACsec-capable IP phones.

• Policy Decision Point (PDP): A policy decision point is responsible for making access control decisions. The PDP provides features such as 802.1x, MAB, and Web authentication. The PDP supports authorization and enforcement through VLAN, DACL, and security group access (SGACL/SXP/SGT).

In the Cisco TrustSec solution, the Cisco Identity Services Engine (ISE) acts as the PDP. The Cisco ISE provides identity and access control policy functionality.

• Policy Information Point (PIP): A policy information point is a source that provides external information (for example, reputation, location, and LDAP attributes) to policy decision points.

Policy information points include devices such as Session Directory, Sensors IPS, and Communication Manager.

• Policy Administration Point (PAP): A policy administration point defines and inserts policies into authorization system. The PAP acts as an identity repository, by providing Cisco TrustSec tag to user identity mapping and Cisco Trustsec tag to server resource mapping.

In the Cisco TrustSec solution, the Cisco Secure Access Control System (a policy server with integrated 802.1x and SGT support) acts as the PAP.

• Policy Enforcement Point (PEP): A policy enforcement point is the entity that carries out the decisions (policy rules and actions) made by the PDP for each AR. PEP devices learn identity information through the primary communication path that exists across networks. PEP devices learn the identity attributes of each AR from many sources, such as end-point agents, authorization servers, peer-enforcement devices, and network flows. In turn, PEP devices use SXP to propagate IP-SGT mappings to mutually-trusted peer devices across the network.

Policy enforcement points include network devices such as Catalyst switches, routers, firewalls (specifically the ASA), servers, VPN devices, and SAN devices.

Security policy enforcement is based on security group name. Compared to traditional IP-based policies configured on firewalls, identity-based policies are configured based on user and device identities. For example, mktg-contractor is allowed to access mktg-servers; mktg-corp-users are allowed to access mktg-server and corp-servers.

The benefits of this type of deployment include:

• User group and Resource is defined and enforced using a single object (SGT) - simplified policy management.

• User identity and resource identity are retained throughout the Cisco Trustsec capable switch infrastructure.

Implementing Cisco TrustSec allows you to configure security policies that support server segmentation and includes the following features:

• A pool of servers can be assigned an SGT for simplified policy management.

• The SGT information is retained within the infrastructure of Cisco Trustsec capable switches.

• The ASA can leverage the IP-SGT mapping for policy enforcement across the Cisco TrustSec domain.

• Deployment simplification is possible because 802.1x authorization for servers is mandatory.

How the ASA Enforces Security Group Based Policies

Note	User-based security policies and security-group based policies can coexist on the ASA. Any combination of network, user-based, and security-group based attributes can be configured in a security policy.

To configure the ASA to function with Cisco TrustSec, you must import a Protected Access Credential (PAC) file from the ISE.

Importing the PAC file to the ASA establishes a secure communication channel with the ISE. After the channel is established, the ASA initiates a PAC secure RADIUS transaction with the ISE and downloads Cisco TrustSec environment data (that is, the security group table). The security group table maps SGTs to security group names. Security group names are created on the ISE and provide user-friendly names for security groups.

Note	From version 4.23 onwards, Cisco Security Manager supports the retrieval of more than 20 Security Group Tags (SGTs) from ISE server in ACL and AAA policies. You can also use underscores in the search text box in SGT and User fields, to reduce the effort of searching usernames with underscores.

Note	For more information about the Cisco Identity Services Engine, see http://www.cisco.com/en/US/products/ps11640/index.html

The first time that the ASA downloads the security group table, it walks through all entries in the table and resolves all the security group names included in security policies that have been configured on it; then the ASA activates those security policies locally. If the ASA cannot resolve a security group name, it generates a syslog message for the unknown security group name.

The following figure shows how a security policy is enforced in Cisco TrustSec.

1. An end-point device connects to an access layer device directly or via remote access and authenticates with Cisco TrustSec.

2. The access layer device authenticates the end-point device with the ISE by using authentication methods such as 802.1X or web authentication. The end-point device passes role and group membership to classify the device into the appropriate security group.

3. The access layer device uses SXP to propagate the IP-SGT mapping to the upstream devices.

4. The ASA receives the packet and looks up the SGTs for the source and destination IP addresses using the IP-SGT mapping passed by SXP.

If the mapping is new, the ASA records it in its local IP-SGT Manager database. The IP-SGT Manager database, which runs in the control plan, tracks IP-SGT mappings for each IPv4 or IPv6 address. The database records the source from which the mapping was learned. The peer IP address of the SXP connection is used as the source of the mapping. Multiple sources can exist for each IP-SGT mapping.

If the ASA is configured as a Speaker, the ASA transmits all IP-SGT mappings to its SXP peers. See About Speaker and Listener Roles.

• If a security policy is configured on the ASA with that SGT or security group name, the ASA enforces the policy. (You can create security policies on the ASA that include SGTs or security group names. To enforce policies based on security group names, the ASA needs the security group table to map security group names to SGTs.)

If the ASA cannot find a security group name in the security group table and it is included in a security policy, the ASA considers the security group name unknown and generates a syslog message. After the ASA refreshes the security group table from the ISE and learns the security group name, the ASA generates a syslog message indicating that the security group name is known.

The Security-group eXchange Protocol (SXP) is used to send and receive IP-SGT mappings to and from other network devices. Employing SXP allows security devices and firewalls to learn identity information from access switches without the need for hardware upgrades or changes. SXP can also be used to pass IP-SGT mappings from upstream devices (such as datacenter devices) back to the downstream devices.

When configuring an SXP connection to an SXP peer, you must designate the device as a Speaker or a Listener for that connection so that it can exchange identity information:

• Speaker mode—configures the device so that it can forward all active IP-SGT mappings to upstream devices for policy enforcement.

• Listener mode—configures the device so that it can receive IP-SGT mappings from downstream devices (SGT-capable switches) and use that information in creating policy definitions.

If one end of an SXP connection is configured as Speaker, then the other end must be configured as a Listener, and vice versa. If both devices on each end of an SXP connection are configured with the same role (either both as Speakers or both as Listeners), the SXP connection will fail and the device will generate a system log message.

Configuring the device to be both a Speaker and a Listener for an SXP connection can cause SXP looping, meaning that SXP data can be received by an SXP peer that originally transmitted it.

As part of configuring SXP, you configure an SXP reconcile timer. After an SXP peer terminates its SXP connection, the device starts a hold down timer. Only SXP peers designated as Listener devices can terminate a connection. If an SXP peer connects while the hold down timer is running, the device starts the reconcile timer; then, the device updates the IP-SGT mapping database to learn the latest mappings.

In any policy or policy object that allows the specification of security groups, whether directly or through the selection of a TrustSec security group object, you can click the Select button next to the Security Groups field to help you enter the information.

In the Security Group Selector dialog box, you can define the content of the Security Groups field by populating the Members in Group list. To populate the list, do any combination of the following:

• In Available Security Group, select an existing object and click the Add >> button between the lists. If the desired object does not exist, you can click the Add (+) button below the list to create a new object. You can also select an object and click the Edit (pencil) button to modify it or to examine its contents.

• In Search name/tag, select a security group from the ISE server configured in the ISE Settings administrative options. You must configure the settings before you can select a name or tag (see ISE Settings Page).

To find a security group, enter a search string. Then, click Search to find matches. A name is considered a match if the string appears anywhere within the security group name.

To add the security group, select it in the list and click the Add >> button between the lists.

• In Type in comma separated (Name or Tag), first select the type of entry you are making, Name or Tag. Type in a valid security group name or tag number, then click the Add >> button between the lists. Separate multiple names or tags with commas; they are added as separate lines in the members list. When adding multiple names or tags, avoid adding spaces before or after the comma.

Valid security tag numbers are 0-65533 for ASA 9.3+ and 1-65533 for ASA versions less than 9.3.

• To remove an item from the object, select it in the Members list and click the << Remove button between the lists.

Security group awareness is integrated into the access control entries, or rules, in the ACLs used to provide firewall services. Because the feature is integrated into the ACL, the techniques for adding security group awareness to a firewall policy are the same for all types of firewall policy. This topic provides general guidance on how to incorporate security group awareness into your existing policies, and directs you to more specific information on configuring each type of policy that supports security groups.