Implementing Network Access Control

When to Use

• Enforcing identity-based network access where only authenticated and compliant devices connect to the network
• Implementing zero-trust networking at the access layer with dynamic VLAN assignment based on user role
• Quarantining non-compliant devices that fail endpoint posture checks (missing patches, disabled AV)
• Meeting compliance requirements (PCI-DSS, HIPAA, SOC 2) for network access controls
• Onboarding BYOD devices with automated provisioning and limited network access

Do not use as a standalone security solution without complementary controls, for networks with devices that do not support 802.1X supplicants, or without proper fallback mechanisms for critical infrastructure.

Prerequisites

• RADIUS server (FreeRADIUS, Microsoft NPS, or Cisco ISE) configured with user/device authentication
• Managed switches supporting 802.1X port-based authentication
• Certificate Authority for EAP-TLS certificate distribution (optional but recommended)
• PacketFence or similar NAC platform for posture assessment and remediation
• Active Directory or LDAP directory for centralized user authentication
• DHCP server integration for dynamic IP assignment per VLAN

Workflow

Step 1: Install and Configure FreeRADIUS

# Install FreeRADIUS
sudo apt install -y freeradius freeradius-utils freeradius-ldap

# Configure RADIUS clients (switches that authenticate against RADIUS)
sudo tee /etc/freeradius/3.0/clients.conf << 'EOF'
client switch-core-01 {
    ipaddr = 10.10.100.1
    secret = R4d1u5_S3cr3t_K3y!
    shortname = core-switch
    nastype = cisco
}

client switch-access-01 {
    ipaddr = 10.10.100.10
    secret = R4d1u5_S3cr3t_K3y!
    shortname = access-switch-01
    nastype = cisco
}

client switch-access-02 {
    ipaddr = 10.10.100.11
    secret = R4d1u5_S3cr3t_K3y!
    shortname = access-switch-02
    nastype = cisco
}
EOF

# Configure LDAP module for Active Directory integration
sudo tee /etc/freeradius/3.0/mods-available/ldap << 'EOF'
ldap {
    server = 'ldap://dc01.corp.example.com'
    identity = 'CN=radius-svc,OU=Service Accounts,DC=corp,DC=example,DC=com'
    password = 'ServiceAccountPassword123!'
    base_dn = 'DC=corp,DC=example,DC=com'

    user {
        base_dn = "${..base_dn}"
        filter = "(sAMAccountName=%{%{Stripped-User-Name}:-%{User-Name}})"
    }

    group {
        base_dn = "${..base_dn}"
        filter = "(objectClass=group)"
        membership_attribute = 'memberOf'
    }
}
EOF

sudo ln -s /etc/freeradius/3.0/mods-available/ldap /etc/freeradius/3.0/mods-enabled/ldap

Step 2: Configure VLAN Assignment Policies

# Configure authorization policies for dynamic VLAN assignment
sudo tee /etc/freeradius/3.0/policy.d/vlan-assignment << 'EOF'
# VLAN assignment based on group membership
vlan_assignment {
    if (&LDAP-Group[*] == "CN=IT-Staff,OU=Groups,DC=corp,DC=example,DC=com") {
        update reply {
            Tunnel-Type = VLAN
            Tunnel-Medium-Type = IEEE-802
            Tunnel-Private-Group-ID = "10"
        }
    }
    elsif (&LDAP-Group[*] == "CN=Developers,OU=Groups,DC=corp,DC=example,DC=com") {
        update reply {
            Tunnel-Type = VLAN
            Tunnel-Medium-Type = IEEE-802
            Tunnel-Private-Group-ID = "15"
        }
    }
    elsif (&LDAP-Group[*] == "CN=Finance,OU=Groups,DC=corp,DC=example,DC=com") {
        update reply {
            Tunnel-Type = VLAN
            Tunnel-Medium-Type = IEEE-802
            Tunnel-Private-Group-ID = "20"
        }
    }
    else {
        # Default: Guest VLAN for unknown users
        update reply {
            Tunnel-Type = VLAN
            Tunnel-Medium-Type = IEEE-802
            Tunnel-Private-Group-ID = "40"
        }
    }
}
EOF

# Add vlan_assignment to the authorize section
# Edit /etc/freeradius/3.0/sites-enabled/default
# In the authorize section, add: vlan_assignment

# Configure EAP for 802.1X authentication
sudo tee /etc/freeradius/3.0/mods-available/eap << 'EAPEOF'
eap {
    default_eap_type = peap
    timer_expire = 60
    max_sessions = 4096

    tls-config tls-common {
        private_key_file = /etc/freeradius/3.0/certs/server.key
        certificate_file = /etc/freeradius/3.0/certs/server.pem
        ca_file = /etc/freeradius/3.0/certs/ca.pem
        dh_file = /etc/freeradius/3.0/certs/dh
        cipher_list = "HIGH:!aNULL:!MD5"
        tls_min_version = "1.2"
    }

    peap {
        tls = tls-common

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