Cisco TrustSec provides security improvements to Cisco network devices based on the capability to strongly identify users, hosts, and network devices within a network. TrustSec provides topology-independent and scalable access controls by uniquely classifying data traffic for a particular role. TrustSec ensures data confidentiality and integrity by establishing trust among authenticated peers and encrypting links with those peers.

The key component of Cisco TrustSec is the Cisco Identity Services Engine (ISE). Cisco ISE can provision switches with TrustSec Identities and Security Group ACLs (SGACLs), though these may be configured manually on the switch.

Note	You should manually clear the CTS environment data using the clear cts environment-data command before changing CTS server to a new one. This ensures that you get the updated data while running show cts environment-data command.

Note	SGT inline tagging is not supported when port channel uplink is in use on the controller.

The table below lists the TrustSec features to be eventually implemented on TrustSec-enabled Cisco switches. Successive general availability releases of TrustSec will expand the number of switches supported and the number of TrustSec features supported per switch.

When both ends of a link support 802.1AE MACsec, SAP negotiation occurs. An EAPOL-key exchange occurs between the supplicant and the authenticator to negotiate a cipher suite, exchange security parameters, and manage keys. Successful completion of these tasks results in the establishment of a security association (SA).

Depending on your software version and licensing and link hardware support, SAP negotiation can use one of these modes of operation:

• Galois Counter Mode (GCM)—authentication and encryption

• GCM authentication (GMAC)— GCM authentication, no encryption

• No Encapsulation—no encapsulation (clear text)

• Null—encapsulation, no authentication or encryption

A security group is a group of users, end-point devices, and resources that share access control policies. Security groups are defined by the administrator in Cisco Identity Services Engine (ISE). As new users and devices are added to the Cisco TrustSec domain, the authentication server assigns these new entities to the appropriate security groups. Cisco TrustSec assigns each of the security group a unique 16-bit number whose scope is global in a Cisco TrustSec domain. The number of security groups in a wireless device is limited to the number of authenticated network entities. You do not have to manually configure the security group numbers.

After a device is authenticated, Cisco TrustSec tags any packet that originates from that device with an SGT that contains the security group number of the device. The packet carries this SGT everywhere in the network, in the Cisco TrustSec header.

As the SGT contains the security group of the source, the tag can be referred to as the source SGT (S-SGT). The destination device is also assigned to a security group (destination SG) that can be referred to as the destination SGT (D-SGT), even though the Cisco TrustSec packet does not contain the security group number of the destination device.

You can control the operations that users can perform based on the security group assignments of users and destination resources, using the Security Group Access Control Lists (SGACLs). Policy enforcement in a Cisco TrustSec domain is represented by a permission matrix, with the source security group numbers on one axis and the destination security group numbers on the other axis. Each cell in the matrix body contains an ordered list of SGACLs, which specify the permissions that must be applied to packets originating from the source security group and destined for the destination security group. When a wireless client is authenticated, the controller downloads all the SGACLs in the matrix cells.

When a wireless client connects to the network, the client pushes all the ACLs to the controller .

Cisco TrustSec achieves role-based topology-independent access control in a network by assigning users and devices in the network to security groups and applying access control between the security groups. The SGACLs define access control policies based on the device identities. As long as the roles and permissions remain the same, changes to the network topology do not change the security policy. When a user is added to the wireless group, you simply assign the user to an appropriate security group; the user immediately receives permissions to that group.

The size of ACLs are reduced and their maintenance is simplified with the use of role-based permissions. With Cisco TrustSec, the number of Access Control Entities (ACEs) that are configured is determined by the number of permissions specified, resulting in a much smaller number of ACEs.

To know the list of Cisco APs that support SGACL, see the release notes: https://www.cisco.com/c/en/us/support/wireless/catalyst-9800-series-wireless-controllers/products-release-notes-list.html

The scenarios supported for SGACLs on the Cisco Catalyst 9800 Series Wireless Controller are:

• Wireless-to-wireless (within Enterprise network):

  • Flex mode with local switching—SGACL enforcement is done on the egress AP when a packet leaves from a source wireless network to a destination wireless network.

  • Flex mode with central switching—SGACL enforcement is done on the egress AP. To achieve this, controller should export IP address to security group tag (IP-SGT) binding over SGT Exchange Protocol (SXP).

• Wired-to-wireless (DC-to-Enterprise network)—Enforcement takes place when a packet reaches the destination AP.

• Wireless-to-wired (Enterprise network-to-DC)—Enforcement takes place on the uplink switch when a packet reaches the ingress of the wired network.

Inline tagging is a transport mechanism using which a controller or AP understands the source SGT.

Transport mechanism is of two types:

• Central switching—For centrally switched packets, the controller performs inline tagging of all the packets sourced from wireless clients that are associated with the controller, by tagging it with the Cisco Meta Data (CMD) tag. For packets that are inbound from the distribution system, inline tagging also involves the controller stripping off the CMD header from the packet to learn the S-SGT tag. Thereafter, the controller forwards the packet including the S-SGT, for SGACL enforcement.

• Local switching—To transmit locally switched traffic, an AP performs inline tagging for packets that are associated with the AP and sourced from clients. To receive traffic, the AP handles both locally switched packets and centrally switched packets, uses the S-SGT tag for packets, and applies the SGACL policy.

With wireless Cisco TrustSec enabled on the controller , the choice of enabling and configuring SXP to exchange tags with the switches is optional. Both wireless Cisco TrustSec and SXP modes are supported; however, there is no use case to have both wireless Cisco TrustSec (on an AP) and SXP to be in the enabled state concurrently.

Cisco TrustSec access control is implemented using ingress tagging and egress enforcement. At the ingress point to the Cisco TrustSec domain, the traffic from the source is tagged with an SGT containing the security group number of the source entity. The SGT is propagated across the domain with the traffic. At the egress point of the Cisco TrustSec domain, an egress device uses the source SGT (S-SGT) and the security group of the destination entity (D-SGT) to determine the access policy to apply from the SGACL policy matrix.

Policy enforcement can be applied to both central and local switched traffic on an AP. If wired clients communicate with wireless clients, the AP enforces the downstream traffic. If wireless clients communicate with wired clients, the AP enforces the upstream traffic. This way, the AP enforces traffic in both downstream and wireless-to-wireless traffic. You require S-SGT, D-SGT, and ACLs for the enforcement to work. APs get the SGT information for all the wireless clients from the information available on the Cisco ISE server.

Note	A Cisco AP must be in either Listener or Both (Listener and Speaker) mode to enforce traffic because the Listener mode maintains the complete set of IP-SGT bindings. After you enable the enforcement on a an AP, the corresponding policies are downloaded and pushed to the AP.

When a client joins the wireless network (WLAN), its session is managed by the Cisco Catalyst 9800 Series Wireless LAN Controller (WLC) that the AP is connected to is the foreign controller. Auto-Anchor Mobility allows a specific WLAN (for example, Guest WLAN) to be anchored to a particular controller, regardless of the client’s entry point into the network. Auto-Anchor Mobility is the wireless Guest service where all guest traffic tunnels back to the DMZ controller irrespective of where they associate with the network.

In case of Auto-Anchor mobility, the following apply to Cisco TrustSec support:

• Classification: Occurs during authentication and hence on Foreign for Layer 2 security WLANs and on Anchor for Layer 3 security cases.

• Propagation: Always occurs at the Anchor where the client traffic enters the wired network.

• Enforcement: SGACL download and enforcement occurs on Anchor; the Anchor controller must have the connectivity to Cisco Identity Services Engine (ISE) and be registered as Network Access Server (NAS). Enforcement is not supported on foreign controller even when the enforcement CLI is configured on foreign controller.

This feature is supported in local mode and in Flex Central Switching of the controller. Flex mode with local switching and Fabric mode are not supported in guest scenarios as traffic does not go through the controller.

Roaming of a guest client occurs only at Guest Foreign controller and the Guest Anchor remains fixed. The different types of supported roam are Inter-Controller roaming and Intra-Controller roaming. Roaming under WebAuth pending is a special case which is also supported for Central Web Authentication (CWA) and Local Web Authentication (LWA).