Implementing Network Access Control with Cisco ISE

Overview

Cisco Identity Services Engine (ISE) provides centralized network access control through 802.1X authentication, MAC Authentication Bypass (MAB), posture assessment, and guest access management. ISE acts as a RADIUS policy server that evaluates authentication requests from network devices (switches, wireless controllers) and returns authorization policies including VLAN assignments, downloadable ACLs (dACLs), and Security Group Tags (SGTs). This skill covers deploying ISE for enterprise wired 802.1X authentication with Active Directory integration, MAB fallback, posture compliance enforcement, and TrustSec segmentation.

Prerequisites

Cisco ISE 3.1+ appliance or virtual machine (16 CPU cores, 64GB RAM minimum for production)
Cisco switches with 802.1X support (Catalyst 9000 series recommended)
Active Directory domain with user and computer accounts
PKI infrastructure for EAP-TLS certificate-based authentication
DNS and NTP configured consistently across ISE nodes and network devices
Supplicant software on endpoints (Windows native, AnyConnect NAM, or SecureW2)

Core Concepts

802.1X Architecture

The 802.1X framework involves three components:

Component	Role	Example
Supplicant	Client requesting network access	Windows 802.1X client, AnyConnect NAM
Authenticator	Network device controlling port access	Cisco Catalyst switch
Authentication Server	Policy decision engine	Cisco ISE (RADIUS)

Authentication Flow

1. Endpoint connects to switch port
2. Switch sends EAP-Request/Identity to endpoint
3. Endpoint responds with EAP-Response/Identity
4. Switch forwards credentials to ISE via RADIUS Access-Request
5. ISE authenticates against AD/LDAP/internal store
6. ISE evaluates authorization policy
7. ISE returns RADIUS Access-Accept with attributes (VLAN, dACL, SGT)
8. Switch enforces authorization on the port

Authentication Methods

Method	Use Case	Security Level
EAP-TLS	Certificate-based, highest security	High
PEAP-MSCHAPv2	Username/password via AD	Medium
EAP-FAST	Cisco proprietary, fast reauthentication	Medium
MAB	Non-802.1X devices (printers, IP phones)	Low

Implementation Steps

Step 1: Configure ISE for Active Directory Integration

Navigate to Administration > Identity Management > External Identity Sources > Active Directory:

Add AD join point with domain name (e.g., corp.example.com)
Provide domain admin credentials for ISE machine account
Join ISE to the domain
Select AD groups for authorization policies:
- Domain Users - Standard employee access
- Domain Computers - Machine authentication
- IT-Admins - Privileged access
- BYOD-Users - Personal device access

Step 2: Configure Network Devices in ISE

Navigate to Administration > Network Resources > Network Devices:

Name: SW-ACCESS-01
IP Address: 10.0.1.1/32
RADIUS Shared Secret: C0mpl3x$3cretKey!
SNMP Settings: v2c, community string
Device Type: Cisco Switches
Location: Building-A-Floor-1

Create a Network Device Group hierarchy:

Device Type:
  ├── Cisco Switches
  │   ├── Access Layer
  │   └── Distribution Layer
  └── Wireless Controllers
Location:
  ├── Building-A
  └── Building-B

Step 3: Configure Switch for 802.1X

Apply this configuration to the access switch:

! Enable AAA
aaa new-model
aaa authentication dot1x default group radius
aaa authorization network default group radius
aaa accounting dot1x default start-stop group radius
aaa accounting update newinfo periodic 2880

! Configure RADIUS server
radius server ISE-PRIMARY
 address ipv4 10.0.5.10 auth-port 1812 acct-port 1813
 key 0 C0mpl3x$3cretKey!
 automate-tester username radius-test probe-on

radius server ISE-SECONDARY
 address ipv4 10.0.5.11 auth-port 1812 acct-port 1813
 key 0 C0mpl3x$3cretKey!
 automate-tester username radius-test probe-on

aaa group server radius ISE-GROUP
 server name ISE-PRIMARY
 server name ISE-SECONDARY
 deadtime 15
 ip radius source-interface Loopback0

! Enable 802.1X globally
dot1x system-auth-control

! Enable RADIUS CoA (Change of Authorization)
aaa server radius dynamic-author
 client 10.0.5.10 server-key C0mpl3x$3cretKey!
 client 10.0.5.11 server-key C0mpl3x$3cretKey!

! Enable device tracking for IP-to-MAC mapping
device-tracking tracking auto-source

! Configure access port template
interface range GigabitEthernet1/0/1-48
 description 802.1X Access Port
 switchport mode access
 switchport access vlan 100

 ! Authentication settings
 authentication host-mode multi-auth
 authentication order dot1x mab
 authentication priority dot1x mab
 authentication port-control auto
 authentication periodic
 authentication timer reauthenticate server
 authentication timer inactivity server dynamic
 authentication violation restrict

 ! 802.1X settings
 dot1x pae authenticator
 dot1x timeout tx-period 10
 dot1x max-reauth-req 2

 ! MAB fallback
 mab

 ! Enable spanning-tree portfast (required for timely auth)
 spanning-tree portfast

 ! Apply pre-auth ACL
 ip access-group PRE-AUTH-ACL in

! Pre-authentication ACL (allow DHCP, DNS, ISE portal)
ip access-list extended PRE-AUTH-ACL
 permit udp any any eq 67
 permit udp any any eq 68
 permit udp any any eq 53
 permit tcp any host 10.0.5.10 eq 8443
 permit tcp any host 10.0.5.11 eq 8443
 deny ip any any

Step 4: Configure ISE Authentication Policy

Navigate to Policy > Policy Sets:

Authentication Policy:

Rule Name	Condition	Allowed Protocols	Identity Source
Dot1X-EAP-TLS	Radius:EAP-Type EQUALS EAP-TLS	EAP-TLS	AD with Certificate
Dot1X-PEAP	Radius:EAP-Type EQUALS PEAP	PEAP-MSCHAPv2	Active Directory
MAB	Radius:Service-Type EQUALS Call-Check	MAB Lookup	Internal Endpoints
Default	Default	Default	Deny Access

Step 5: Configure ISE Authorization Policy

Authorization Policy:

Rule Name	Condition	Authorization Profile
IT-Admin-Wired	AD:Group EQUALS IT-Admins AND Dot1X	VLAN10-FullAccess
Employee-Compliant	AD:Group EQUALS Domain Users AND Posture:Compliant	VLAN100-Corporate
Employee-NonCompliant	AD:Group EQUALS Domain Users AND Posture:NonCompliant	VLAN200-Remediation
Printer-MAB	EndpointIdentityGroup EQUALS Printers	VLAN150-Printers
IP-Phone-MAB	EndpointIdentityGroup EQUALS IP-Phones	VLAN50-Voice
BYOD-Onboarding	AD:Group EQUALS BYOD-Users AND !Registered	BYOD-Portal-Redirect
Guest-Access	GuestEndpointGroup EQUALS GuestEndpoints	VLAN300-Guest
Default	Default	DenyAccess

Authorization Profiles:

Profile: VLAN100-Corporate
  VLAN: 100
  dACL: PERMIT_ALL
  SGT: Employees (0x0005)
  Reauthentication Timer: 28800

Profile: VLAN200-Remediation
  VLAN: 200
  dACL: REMEDIATION-ACL (allow only remediation server access)
  Web Redirection: Posture Discovery
  Reauthentication Timer: 300

Profile: DenyAccess
  Access Type: ACCESS_REJECT

Step 6: Configure Posture Assessment

Navigate to Work Centers > Posture:

Posture Conditions:

- Windows Firewall Enabled (Registry check)
- Antivirus Running and Updated (AV compound condition)
- OS Patch Level Current (Windows Update check)
- Disk Encryption Enabled (BitLocker check)

Posture Requirements:

Requirement: Corporate-Windows-Compliance
  OS: Windows All
  Conditions: Windows Firewall AND Antivirus AND OS Patches
  Remediation: Auto-remediate with AnyConnect ISE Posture Module

Posture Policy:

Rule: Windows-Endpoints
  Identity Group: Any
  OS: Windows All
  Requirement: Corporate-Windows-Compliance

Step 7: Configure TrustSec Segmentation

Enable SGT-based segmentation:

! On switch - enable CTS
cts credentials id SW-ACCESS-01 password CtsP@ss
cts role-based enforcement
cts role-based sgt-map 10.0.100.0/24 sgt 5

! Download SGT policy from ISE
cts role-based permissions

ISE TrustSec Matrix (SGACL):

Source SGT	Destination SGT	Policy
Employees (5)	Servers (10)	Permit_HTTP_HTTPS
Employees (5)	PCI_Zone (15)	Deny_All
IT-Admins (3)	Servers (10)	Permit_All
Guest (7)	Internet (99)	Permit_HTTP_HTTPS
Guest (7)	Servers (10)	Deny_All

Troubleshooting

# On switch - verify authentication status
show authentication sessions
show authentication sessions interface Gi1/0/1 details
show dot1x all

# Check RADIUS connectivity
test aaa server radius ISE-PRIMARY username testuser password testpass

# On ISE - check live logs
# Navigate to Operations > RADIUS > Live Logs
# Filter by MAC address or username
# Review Authentication Details for failure reason

# Common failure reasons:
# 12514 - EAP-TLS handshake failed (certificate issue)
# 22056 - Subject not found in identity store
# 24408 - User not found in Active Directory
# 24454 - User password expired

Best Practices

Monitor Mode First - Deploy in monitor mode (open authentication) before closed mode enforcement
Low-Impact Mode - Use authentication open with pre-auth dACLs for gradual rollout
MAB Database - Pre-populate endpoint database with known MAC addresses for printers, phones
Profiling - Enable ISE profiling to automatically classify endpoints by type
CoA Support - Ensure Change of Authorization is configured for dynamic policy updates
High Availability - Deploy ISE in a Primary/Secondary node pair with PAN failover
Certificate Infrastructure - Use machine certificates for EAP-TLS for strongest authentication

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