mediumMultiple Choice
350-401 Practice Question: In Cisco TrustSec, which component is responsible…
In Cisco TrustSec, which component is responsible for assigning a Security Group Tag (SGT) to a user or device based on authentication?
⚠ Common exam trap
Cisco often tests the misconception that the SGT is derived from the VLAN or assigned by the switch dynamically, when in fact it is a policy-based attribute returned by the RADIUS server (ISE) during authentication.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The RADIUS server (ISE) assigns the SGT during authentication.
In Cisco TrustSec, the Security Group Tag (SGT) is assigned by the RADIUS server—specifically Cisco ISE—during the 802.1X authentication process. When a user or device authenticates, ISE evaluates the authentication result and policy, then returns the SGT as a RADIUS attribute (e.g., Cisco-AVPair or MS-MPPE-Send-Key) in the Access-Accept message. The switch then uses this SGT to enforce security group-based access control (SGACL) for traffic from that endpoint.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The RADIUS server (ISE) assigns the SGT during authentication.
Why this is correct
During 802.1X authentication, the endpoint credentials are sent to ISE (the policy server). Upon validation, ISE returns a RADIUS Access-Accept message that carries the Security Group Tag (SGT) as a Cisco AV-pair (e.g., cisco-av-pair=...). The switch then programs this SGT for the session and uses it to enforce TrustSec policies, such as SGACLs. This ensures the classification is centralized, consistent, and dynamic based on the user or device identity.
- ✗
The switch dynamically assigns the SGT based on the MAC address.
Why it's wrong here
The switch is only an enforcement point in TrustSec; it does not make policy decisions and cannot derive a security classification from a MAC address alone. MAC addresses are easily spoofed and carry no user or device role information, so a dynamic MAC-based assignment would create a static, insecure mapping. Instead, the switch receives the SGT from ISE in the RADIUS Access-Accept, and its local role is limited to applying that tag and the associated SGACL rules.
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The endpoint device sends its SGT in the EAPOL-Start message.
Why it's wrong here
EAPOL-Start is a low-level EAP message sent by the endpoint to initiate 802.1X authentication; it contains only a basic EAP header and no application payload, so it cannot carry an SGT. Moreover, at the time EAPOL-Start is sent, the endpoint has not yet provided any credentials, so no identity exists to derive an SGT from. The SGT is a post-authentication classification assigned by ISE and delivered to the switch in the RADIUS Access-Accept, never in an EAPOL message.
- ✗
The SGT is derived from the VLAN ID assigned to the port.
Why it's wrong here
VLAN assignment is a Layer 2 concept that groups ports into broadcast domains, while the SGT is a 16-bit security classification that crosses Layer 2 boundaries and maps to security group ACLs. Although ISE can return both a VLAN and an SGT in the same Access-Accept, they are independent attributes: the VLAN controls network reachability, while the SGT controls security policy. The switch does not derive one from the other; an endpoint in the same VLAN can have different SGTs based on its identity.
Quick reference
AAA Protocol Comparison
| Protocol | Port(s) | Encryption | Transport | Primary Use |
|---|---|---|---|---|
| RADIUS | 1812 / 1813 | Password only | UDP | Network access control |
| TACACS+ | 49 | Full packet | TCP | Device administration |
| Diameter | 3868 | Full session | TCP / SCTP | Carrier / mobile networks |
| 802.1X | — | EAP-based | Layer 2 | Port-based access control |
TACACS+ encrypts the entire packet; RADIUS only encrypts the password field — a key exam distinction.
Go deeper
Related to this question
Learn chapter
Network Access Control and AAA
Key term
802.1X Authentication
802.1X is a network access control protocol that prevents unauthorized devices from connecting to a wired or wireless network by requiring them to authenticate before gaining access.
Key term
RADIUS vs TACACS+
RADIUS and TACACS+ are two network protocols used to verify user identities and control access to network devices and services, with different approaches to security and flexibility.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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