32 Wireless Security · CCNA

Exam topics covered

5.9 Describe wireless security protocols (WPA, WPA2, and WPA3)

5.10 Configure and verify WLAN within the GUI using WPA2 PSK

Foundation. A wired LAN has a natural boundary: to connect, an attacker has to get into the building and find a live port. Radio waves ignore walls, so anyone in the car park can hear every frame on your WLAN. Wireless security therefore has to do two jobs that physical security does for Ethernet: authenticate who may associate, and encrypt every frame so that eavesdroppers learn nothing. This chapter explains the authentication methods (open, pre-shared key and 802.1X/EAP), the encryption protocols (TKIP, CCMP and GCMP), how WPA, WPA2 and WPA3 package them, and then walks through configuring and verifying a WPA2- PSK WLAN in the GUI of a wireless LAN controller, exactly as blueprint topic 5.10 requires.

32.1 Why Wireless Needs Its Own Security

Three properties of wireless shape its security. The medium is unbounded, so eavesdropping is passive and undetectable. Anyone can transmit, so attackers can run a rogue AP or an evil twin (an AP broadcasting your SSID) to lure clients. And management frames such as deauthentication were historically unprotected, allowing trivial denial-of-service. A secure WLAN therefore needs authentication (ideally mutual, so clients do not join an evil twin), encryption of every data frame, message integrity against alteration and replay, and protection of management frames against forged deauthentication.

32.2 Wireless Authentication Methods

32.2.1 Open authentication and WEP

Open system authentication, from the original 802.11 standard, accepts any client. Café and guest networks still use it, often with a web portal after association; without extra protection all traffic is unencrypted.

The original 802.11 encryption, WEP (Wired Equivalent Privacy), used RC4 with a static 40- or 104-bit key shared by all clients. Its key can be recovered from captured traffic in minutes; it is completely broken.

32.2.2 Pre-shared key (Personal mode)

With a pre-shared key (PSK), every client and the AP or controller are configured with the same passphrase of 8 to 63 ASCII characters (or 64 hexadecimal digits). The passphrase, combined with the SSID, is turned into a 256-bit pairwise master key (PMK). The client and AP then perform the four-way handshake: they exchange random numbers (nonces) and each proves that it knows the PMK without sending it, and both derive fresh pairwise transient keys (PTK) that encrypt that client's unicast traffic. A group key for broadcast and multicast is delivered in the same handshake.

PSK suits homes and small offices, hence the name Personal mode. But everyone shares one secret, so you cannot revoke one user, and anyone who captures a four-way handshake can run an offline dictionary attack against a weak passphrase. WPA3 fixes the latter with SAE (section 32.4).

Client (supplicant) AP / WLC

both know PMK (from PSK + SSID, or 802.1X)

1. ANonce
2. SNonce + MIC (client has derived PTK)
3. Install PTK, encrypted GTK + MIC
4. ACK (keys installed, encryption starts)

Figure 32-1 The four-way handshake derives per-session keys from the PMK without ever transmitting it. 32.2.3 802.1X/EAP (Enterprise mode)

Enterprise mode replaces the shared passphrase with individual credentials checked by a RADIUS server, using the same 802.1X framework you met for wired ports in Chapter 28. The three roles are:

Supplicant: the wireless client.

Authenticator: the WLC (or an autonomous AP), which blocks the client's data traffic until authentication succeeds and relays EAP messages.

Authentication server (AS): a RADIUS server such as Cisco ISE, which validates the credentials.

The credentials are carried by the Extensible Authentication Protocol (EAP): EAPoL over the air, EAP inside RADIUS on the wired side. On success the server sends an Access-Accept with keying material, so the WLC and client share a unique PMK and run the four-way handshake. Every user gets unique keys and can be disabled centrally.

Wlc

Supplicant Authenticator (WLC) Auth server (RADIUS)

1. 802.11 open auth + association
2. EAP-Request/Identity
3. EAP-Response/Identity RADIUS Access-Request
4. EAP method exchange (e.g. PEAP or EAP-TLS) relayed by the WLC:

EAPoL over the air, EAP inside RADIUS on the wired side

5. Access-Accept + key material
6. EAP-Success
7. Four-way handshake (PMK to PTK)
8. Encrypted data allowed

Figure 32-2 802.1X/EAP authentication on a WLAN, followed by the four-way handshake.

32.2.4 EAP methods

EAP is a framework; the method determines the credentials and how they are protected:

Table 32-1 Common EAP methods

Method Credentials Notes

LEAP Username/password Cisco's early (pre-WPA) method, based on MS-CHAP.

Vulnerable to dictionary attacks; deprecated. Of historical

interest only.

EAP-FAST Username/password
plus a PAC
Cisco-developed replacement for LEAP. A Protected Access
Credential (PAC), provisioned in phase 0, builds a TLS tunnel
(phase 1) in which the user authenticates (phase 2). No

certificates required.

PEAP Server certificate;
username/password
inside the tunnel

The server proves its identity with a certificate and builds a TLS tunnel; the client then authenticates inside it, usually with MS-CHAPv2 (or GTC). Clients need no certificate. Very widely

used.

EAP-TLS Certificates on both
server and client
Mutual certificate authentication, no passwords. The most
secure method, but requires a PKI to issue every client a

certificate.

Exam alert

EAP-TLS is the method that requires a certificate on the client. PEAP requires only a server certificate. EAP-FAST uses a PAC instead of certificates. LEAP is the old, insecure Cisco method. And in 802.1X, the WLC is the authenticator, not the authentication server.

32.3 Encryption and Integrity Protocols

Authentication produces keys; an encryption protocol uses them to protect frames: TKIP (Temporal Key Integrity Protocol) was a stopgap to fix WEP on existing hardware. It still uses RC4 but adds per-packet key mixing, a sequence counter against replay and a message integrity check (MIC, called “Michael”). It has known weaknesses and is deprecated; using it also limits 802.11n/ac data rates.

CCMP (Counter Mode with CBC-MAC Protocol) uses the AES cipher in counter mode for encryption and CBC-MAC for integrity. It is mandatory in WPA2. In GUIs it is usually labelled simply “AES”.

GCMP (Galois/Counter Mode Protocol) also uses AES, combining encryption and authentication more efficiently, and supports 256-bit keys. GCMP-256 is used by WPA3- Enterprise's 192-bit mode and by 802.11ac/ax for higher performance.

32.4 WPA, WPA2 and WPA3

The Wi-Fi Alliance certifies products for interoperable security suites named WPA. Each generation supports a Personal mode (shared key) and an Enterprise mode (802.1X/EAP).

Table 32-2 WPA, WPA2 and WPA3 compared

Psk psk sae

Simultaneous Authentication of Equals (SAE) replaces PSK in WPA3-Personal. Users still type a passphrase, but the client and AP run a Diffie-Hellman-style “Dragonfly” exchange that proves both know it and yields a fresh, unique PMK. A captured handshake gives an attacker nothing to test, defeating offline dictionary attacks, and old sessions stay safe even if the passphrase later leaks (forward secrecy).

Protected Management Frames (PMF), from 802.11w, protects deauthentication and disassociation frames. WPA3 makes it mandatory, stopping forged-deauthentication DoS attacks.

Opportunistic Wireless Encryption (OWE), marketed as Wi-Fi Enhanced Open, encrypts open networks: no password, but a Diffie-Hellman exchange during association gives each client unique keys. It stops eavesdropping, though not an evil twin, since there is no authentication.

For migration, WPA3 supports a transition mode on one SSID that accepts both WPA2-PSK and WPA3-SAE clients.

WEP (1999)
RC4, static key
broken
WPA (2003)

Tkip + mic

deprecated

WPA2 (2004)

Ccmp / aes

PSK or 802.1X
WPA3 (2018)
SAE, PMF required,
GCMP-256 option; OWE

Each generation offers Personal (shared secret) and Enterprise (802.1X/EAP) modes

Figure 32-3 The evolution of Wi-Fi security.

Exam alert

Link each protocol to its key feature: WPA = TKIP; WPA2 = AES-CCMP; WPA3 = SAE, mandatory PMF and GCMP-256 for 192-bit Enterprise. SAE replaces PSK; it is what defeats offline dictionary attacks. OWE (Enhanced Open) encrypts open networks without a password.

32.5 Configuring a WPA2-PSK WLAN in the WLC GUI

Blueprint topic 5.10 asks you to configure and verify a WLAN in the GUI. The figures are generic mock-ups of an AireOS-style WLC GUI; on Catalyst 9800 (IOS XE) controllers the same settings are under Configuration > Tags & Profiles > WLANs. The goal: a WLAN called CORP, mapped to the controller's dynamic interface for VLAN 20, secured with WPA2 Personal, AES encryption and a pre-shared key.

First make sure the dynamic interface (here named vlan20 , 10.20.0.0/24) exists under Controller > Interfaces, and that the switch port to the WLC trunks VLAN 20 (Chapter 18).

32.5.1 Step 1: create the WLAN

Open the WLANs tab, choose Create New from the drop-down and click Go. Enter the type, a profile name (used internally on the controller), the SSID (what clients see) and a WLAN ID. MONITOR WLANs CONTROLLER WIRELESS SECURITY MANAGEMENT

WLANs > New
Type WLAN ▾
Profile Name CORP

Ssid corp

ID 1 ▾

< Back Apply

Figure 32-4 Creating a new WLAN: profile name, SSID and WLAN ID.

32.5.2 Step 2: General tab

After Apply, the WLAN edit page opens on the General tab. Enable the WLAN (it is created disabled), choose the interface that maps the SSID to VLAN 20, and leave Broadcast SSID enabled so clients can discover it. The Security Policies line shows the current security setting, which defaults to WPA2 with 802.1X.

WLANs > Edit 'CORP'
General Security QoS Policy-Mapping Advanced
Profile Name CORP
Type WLAN

Ssid corp

Figure 32-5 General tab: enable the WLAN and map it to the VLAN 20 dynamic interface.

32.5.3 Step 3: Security > Layer 2

Click the Security tab, then the Layer 2 sub-tab. Set Layer 2 Security to WPA+WPA2. Under WPA+WPA2 Parameters, check WPA2 Policy only (leave the legacy WPA Policy unchecked) and select AES encryption, with TKIP unchecked. Under Authentication Key Management, clear 802.1X and enable PSK.

Figure 32-6 Security > Layer 2: WPA2 policy, AES encryption, PSK key management.

32.5.4 Step 4: PSK format and key, then Apply

When PSK is enabled, the PSK Format field appears below Authentication Key Management. Choose ASCII and enter a passphrase of 8 to 63 characters (or choose HEX and enter exactly 64 hexadecimal digits). Click Apply at the top right of the page; the controller warns that changing the WLAN will disconnect any associated clients. Finally, click Save Configuration so the change survives a reboot.

Figure 32-7 Entering the ASCII pre-shared key and applying the change.

Watch out

Three common mistakes: forgetting to check the WLAN Status: Enabled box on the General tab; leaving 802.1X checked under Authentication Key Management alongside PSK, so clients may be asked for credentials they do not have; and mapping the WLAN to the management interface instead of the intended client VLAN.

32.5.5 Step 5: verify client association

Connect a client to SSID CORP using the passphrase, then check in the GUI. The WLANs page lists the WLAN as enabled with its security policy. Monitor > Clients lists every associated client with the AP, WLAN and protocol; clicking a client's MAC address shows its details, including the IP address learned and the security that was negotiated.

MONITOR > Clients

Current Filter None

Client MAC Addr IP Address AP Name WLAN Profile Protocol Status Auth a4:83:e7:1c:22:5f 10.20.0.51 AP-Floor2-East CORP 802.11ac(5 GHz) Associated Yes 3c:22:fb:90:7a:11 10.20.0.64 AP-Floor2-West CORP 802.11ax(5 GHz) Associated Yes f0:18:98:4e:03:c2 10.20.0.72 AP-Floor1-Lobby CORP 802.11n(2.4 GHz) Associated Yes Clients > Detail: a4:83:e7:1c:22:5f

Vlan 20

Figure 32-8 Monitor > Clients and client detail: associated, policy RUN, WPA2 with CCMP (AES) and PSK.

The controller CLI shows the same; a client stuck in a state other than RUN has not completed the four-way handshake, usually because of a wrong passphrase.

WLC1 — ssh

(Cisco Controller) >show client detail a4:83:e7:1c:22:5f

Client MAC Address............................... a4:83:e7:1c:22:5f Wireless LAN Profile Name........................ CORP

IP Address....................................... 10.20.0.51
Policy Manager State............................. RUN
Policy Type...................................... WPA2
Authentication Key Management.................... PSK

Encryption Cipher................................ CCMP-128 (AES)

Figure 32-9 Verifying the client from the WLC CLI. (Output is illustrative of an AireOS 8.x controller; GUI figures are generic mock-ups.)

LAB Build and verify a WPA2-PSK WLAN

Goal: create WLAN CORP on WLC1, mapped to VLAN 20, using WPA2-Personal with AES and an ASCII passphrase, and confirm that a laptop associates and receives an address in 10.20.0.0/24.

Wlc

Wlc1

mgmt 10.10.0.5
trunk VLAN 10,20
SW1

Dhcp 10.20.0.0/24

access VLAN 10 (CAPWAP)

AP1

Ssid corp

Figure 32-10 Wireless lab topology.

1. Confirm AP1 is joined to WLC1 (Wireless > All APs) and that dynamic interface vlan20 exists.
2. Create and configure WLAN CORP exactly as in Figures 32-4 to 32-7 (ID 1, Enabled, interface vlan20, WPA2 Policy, AES, PSK only, ASCII passphrase). Apply, then Save Configuration.
3. On the laptop, join CORP and enter the passphrase.

Expected results: the WLAN shows [WPA2][Auth(PSK)] and Enabled; Monitor > Clients lists the laptop on CORP with Status Associated and Auth Yes; client detail shows Policy Manager State RUN, WPA2, PSK, CCMP (AES) and an IP address in 10.20.0.0/24. Enter a wrong passphrase on a second client and observe that it never reaches RUN. Chapter review

Key terms

open authentication

Wep

pre-shared key

four-way handshake

Pmk

Ptk

Personal mode
Enterprise mode
802.1X
supplicant
authenticator

Eap

Leap

Eap-fast

Peap

Eap-tls

Tkip

Ccmp

Gcmp

Sae

Pmf

Owe

1. Which encryption protocol is mandatory in WPA2?

A. TKIP
B. WEP
C. CCMP (AES)
D. RC4

2. Which WPA3 feature replaces PSK and prevents offline dictionary attacks against captured handshakes?

A. PMF
B. SAE
C. OWE
D. TKIP

3. Which two features are mandatory or introduced with WPA3? (Choose two.)

A. Protected Management Frames
B. TKIP encryption
C. Simultaneous Authentication of Equals
D. LEAP
E. WEP compatibility

4. In an 802.1X WLAN, which role does the wireless LAN controller perform?

A. Supplicant
B. Authenticator
C. Authentication server
D. Certificate authority

5. Which EAP method requires a certificate on every client?

A. PEAP
B. EAP-FAST
C. LEAP
D. EAP-TLS

6. Which EAP method uses a Protected Access Credential instead of certificates?

A. EAP-FAST
B. EAP-TLS
C. PEAP
D. WEP

7. What is the purpose of the four-way handshake?

A. To authenticate the user against RADIUS
B. To derive and install encryption keys from the PMK
C. To assign an IP address
D. To associate the client with the strongest AP

8. Which technology encrypts traffic on an open guest WLAN without requiring a password?

A. WPA2-PSK
B. OWE (Enhanced Open)
C. WEP
D. MAC filtering

9. In the WLC GUI, where do you select PSK as the authentication key management method?

A. General tab
B. Security > Layer 2
C. Security > Layer 3
D. QoS tab

10. An engineer created WLAN CORP with WPA2-PSK, but clients do not see the SSID. All other settings are correct. What is most likely missing?

A. The WLAN Status: Enabled check box
B. TKIP encryption
C. An AAA server
D. PMF set to Required

11. Which two values can be entered as a WPA2 pre-shared key? (Choose two.)

A. 8 to 63 ASCII characters
B. Exactly 64 hexadecimal digits
C. 4 to 7 ASCII characters
D. A 40-bit WEP key
E. A client certificate

12. A client detail page shows Policy Manager State RUN, Policy Type WPA2, Encryption Cipher CCMP (AES), Key Mgmt PSK. What does this indicate?

A. The client failed authentication.
B. The client authenticated with 802.1X.
C. The client completed WPA2-Personal authentication and is passing traffic.
D. The client is using TKIP.

13. Which protocol was an interim fix for WEP that still uses RC4?

A. CCMP
B. GCMP
C. TKIP
D. SAE

Answers

1. C. WPA2 requires CCMP, which uses AES. TKIP is optional and deprecated.
2. B. SAE uses a Dragonfly exchange, so a captured handshake cannot be attacked offline.
3. A, C. WPA3 mandates PMF and uses SAE for Personal mode.
4. B. The WLC is the authenticator; the RADIUS server is the authentication server.
5. D. EAP-TLS uses mutual certificate authentication. PEAP needs only a server certificate.
6. A. EAP-FAST uses a PAC to build its tunnel.
7. B. The handshake proves both sides hold the PMK and derives the PTK and GTK.
8. B. OWE performs a Diffie-Hellman exchange during association to encrypt open networks.
9. B. Authentication Key Management (802.1X, PSK) is on the Security > Layer 2 tab.
10. A. New WLANs are disabled until Status is checked on the General tab.
11. A, B. A PSK is 8–63 ASCII characters or 64 hex digits.
12. C. RUN means the client completed security and can pass data; PSK and CCMP confirm WPA2-Personal with AES.
13. C. TKIP was designed to run on WEP-era hardware and still uses RC4.