Chapter 20. Authenticating Wireless Clients

This chapter covers the following subjects:

Open Authentication: This section covers authenticating wireless users using no credentials.

Authenticating with Pre-Shared Key: This section covers authenticating clients with a static key that is shared prior to its use.

Authenticating with EAP: This section covers authenticating clients with Extensible Authentication Protocol (EAP).

Authenticating with WebAuth: This section covers authenticating clients through the use of a web page where credentials are entered.

You might remember from studying for the CCNA 200-301 exam that wireless networks can leverage many technologies and protocols to protect information that is sent over the air. For example, the WPA, WPA2, and WPA3 security suites can be used to protect data privacy and integrity. Beyond that, it is also important to identify the two endpoints (the AP and the client device) that use a wireless connection, as well as the end user. This chapter explores three different methods to authenticate wireless clients before they are granted access to a wireless network.

“Do I Know This Already?” Quiz

The “Do I Know This Already?” quiz allows you to assess whether you should read the entire chapter. If you miss no more than one of these self-assessment questions, you might want to move ahead to the “Exam Preparation Tasks” section. Table 20-1 lists the major headings in this chapter and the “Do I Know This Already?” quiz questions covering the material in those headings so you can assess your knowledge of these specific areas. The answers to the “Do I Know This Already?” quiz appear in Appendix A, “Answers to the ‘Do I Know This Already?’ Quiz Questions.”

Table 20-1 “Do I Know This Already?” Section-to-Question Mapping

Foundation Topics Section

Questions

Open Authentication

1–2

Authenticating with Pre-Shared Key

3–6

Authenticating with EAP

7–8

Authenticating with WebAuth

9–10

1. Open Authentication requires the use of which one of the following?

  1. 802.1x

  2. RADIUS

  3. HTTP/HTTPS

  4. Pre-Shared Key

  5. None of the above

2. Open Authentication can be used in combination with which one of the following?

  1. PSK

  2. WebAuth

  3. EAP

  4. 802.1x

3. When PSK authentication is used on a WLAN, without the use of an ISE server, which of the following devices must be configured with the key string? (Choose two.)

  1. One wireless client (each with a unique key string)

  2. All wireless clients

  3. All APs and WLCs

  4. A RADIUS server

4. Which of the following authentication methods does WPA2 personal mode use?

  1. Open Authentication

  2. Pre-Shared Key

  3. EAP

  4. 802.1x

5. Which of the following WPA versions is considered to have the most secure personal mode?

  1. WPA

  2. WPA1

  3. WPA2

  4. WPA3

  5. The personal modes are all equivalent.

6. Pre-Shared Key is used in which of the following wireless security configurations? (Choose all that apply.)

  1. WPA personal mode

  2. WPA enterprise mode

  3. WPA2 personal mode

  4. WPA2 enterprise mode

  5. WPA3 personal mode

  6. WPA3 enterprise mode

7. Which one of the following is used as the authentication method when 802.1x is used on a WLAN?

  1. Open Authentication

  2. WEP

  3. EAP

  4. WPA

8. A Cisco WLC is configured for 802.1x authentication, using an external RADIUS server. The controller takes on which one of the following roles?

  1. Authentication server

  2. Supplicant

  3. Authenticator

  4. Adjudicator

9. When WPA2 enterprise mode is used on a WLAN, where is the supplicant role located?

  1. On the wireless client

  2. On the AP

  3. On the WLC

  4. On the RADIUS server

10. Suppose an enterprise offers a wireless network that guests can use but only after they read and accept an acceptable use policy document. Which one of the following methods can inherently handle this process?

  1. Open Authentication

  2. WPA3 personal

  3. WPA2 enterprise

  4. WebAuth

Answers to the “Do I Know This Already?” quiz:

1 E

2 B

3 B, C

4 B

5 D

6 A, C, E

7 C

8 C

9 A

10 D

Foundation Topics

To join and use a wireless network, wireless clients must first discover a basic service set (BSS) and then request permission to associate with it. At that point, clients should be authenticated by some means before they can become functioning members of a wireless LAN. Why?

Suppose that your wireless network connects to corporate resources where confidential information can be accessed. In that case, only devices known to be trusted and expected should be given access. Guest users, if they are permitted at all, should be allowed to join a different guest WLAN where they can access nonconfidential or public resources. Rogue clients, which are not expected or welcomed, should not be permitted to associate at all. After all, they are not affiliated with the corporate network and are likely to be unknown devices that happen to be within range of your network.

To control access, wireless networks can authenticate the client devices before they are allowed to associate. Potential clients must identify themselves by presenting some form of credentials to the APs. Figure 20-1 shows the basic client authentication process.

A figure illustrates a wireless client authenticated by an AP. This is represented in the form of dialogs between the user and the AP. The AP asks "Who are you?" to which the client replies "I am Joe User". The AP says "OK" and grants access.

Figure 20-1 Authenticating a Wireless Client

Wireless authentication can take many forms. Some methods require only a static text string that is common across all trusted clients and APs. The text string is stored on the client device and presented directly to the AP when needed. What might happen if the device is stolen or lost? Most likely, any user who possesses the device would still be able to authenticate to the network. Other more stringent authentication methods require interaction with a corporate user database. In those cases, the end user must enter a valid username and password—something that would not be known to a thief or an imposter.

The sections that follow explain four types of client authentication you will likely encounter on the CCNP and CCIE Enterprise ENCOR 350-401 exam and in common use. With each type, you will begin by creating a new WLAN on the wireless LAN controller, assigning a controller interface, and enabling the WLAN. Because wireless security is configured on a per-WLAN basis, all of the configuration tasks related to this chapter occurs in the WLAN > Edit Security tab.

Open Authentication

Recall that a wireless client device must send 802.11 authentication request and association request frames to an AP when it asks to join a wireless network. The original 802.11 standard offered only two choices to authenticate a client: Open Authentication and WEP.

Open Authentication is true to its name; it offers open access to a WLAN. The only requirement is that a client must use an 802.11 authentication request before it attempts to associate with an AP. No other credentials are needed.

When would you want to use Open Authentication? After all, it does not sound very secure (and it is not). With no challenge, any 802.11 client may authenticate to access the network. That is, in fact, the whole purpose of Open Authentication—to validate that a client is a valid 802.11 device by authenticating the wireless hardware and the protocol. Authenticating the user’s identity is handled as a true security process through other means.

You have probably seen a WLAN with Open Authentication when you have visited a public location. If any client screening is used at all, it comes in the form of Web Authentication (WebAuth), which is described in the “Authenticating with WebAuth” section of this chapter. A client can associate right away but must open a web browser to see and accept the terms for use and enter basic credentials. From that point, network access is opened up for the client.

To create a WLAN with Open Authentication, first create a new WLAN and map it to the correct VLAN. Go to the General tab and enter the SSID string, apply the appropriate controller interface, and change the status to Enabled.

Next, select the Security tab to configure the WLAN security and user authentication parameters. Select the Layer 2 tab and then use the Layer 2 Security drop-down menu to select None for Open Authentication, as shown in Figure 20-2. In this example, the WLAN is named guest, and the SSID Guest.

A screenshot of the Wireless LAN Controller GUI is shown.

Figure 20-2 Configuring Open Authentication for a WLAN

When you are finished configuring the WLAN, click the Apply button. You can verify the WLAN and its security settings from the WLANs > Edit General tab, as shown in Figure 20-3 or from the list of WLANs, as shown in Figure 20-4. In both figures, the Security Policies field is shown as None. You can also verify that the WLAN status is enabled and active.

A screenshot of the Wireless LAN Controller GUI illustrates the verification of open authentication in the WLAN configuration.

Figure 20-3 Verifying Open Authentication in the WLAN Configuration

A screenshot of the Wireless LAN Controller GUI illustrates verifying from a list of WANs.

Figure 20-4 Verifying Open Authentication from List of WLANs

Authenticating with Pre-Shared Key

To secure wireless connections on a WLAN, you can leverage one of the Wi-Fi Protected Access (WPA) versions—WPA (also known as WPA1), WPA2, or WPA3. Each version is certified by the Wi-Fi Alliance so that wireless clients and APs using the same version are known to be compatible. The WPA versions also specify encryption and data integrity methods to protect data passing over the wireless connections.

All three WPA versions support two client authentication modes, Pre-Shared Key (PSK) or 802.1x, depending on the scale of the deployment. These are also known as personal mode and enterprise mode, respectively. With personal mode, a key string must be shared or configured on every client and AP before the clients can connect to the wireless network. The pre-shared key is normally kept confidential so that unauthorized users have no knowledge of it. The key string is never sent over the air. Instead, clients and APs work through a four-way handshake procedure that uses the pre-shared key string to construct and exchange encryption key material that can be openly exchanged. When that process is successful, the AP can authenticate the client, and the two can secure data frames that are sent over the air.

With WPA-Personal and WPA2-Personal modes, a malicious user can eavesdrop and capture the four-way handshake between a client and an AP. He can then use a dictionary attack to automate the guessing of the pre-shared key. If he is successful, he can then decrypt the wireless data or even join the network, posing as a legitimate user.

WPA3-Personal avoids such an attack by strengthening the key exchange between clients and APs through a method known as Simultaneous Authentication of Equals (SAE). Rather than a client authenticating against a server or AP, the client and AP can initiate the authentication process equally and even simultaneously.

Even if a password or key is compromised, WPA3-Personal offers forward secrecy, which prevents attackers from being able to use a key to unencrypt data that has already been transmitted over the air.

Tip

The personal mode of any WPA version is usually easy to deploy in a small environment or with clients that are embedded in certain devices because a simple text key string is all that is needed to authenticate the clients. Be aware that every device using the WLAN must be configured with an identical pre-shared key, unless PSK with ISE is used. If you ever need to update or change the key, you must touch every device to do so. In addition, the pre-shared key should remain a well-kept secret; you should never divulge the pre-shared key to any unauthorized person. To maximize security, you should use the highest WPA version available on the WLCs, APs, and client devices in your network.

You can configure WPA2 or WPA3 personal mode and the pre-shared key in one step. Navigate to WLANs and select Create New or select the WLAN ID of an existing WLAN to edit. Make sure that the parameters on the General tab are set appropriately.

Next, select the Security > Layer 2 tab. In the Layer 2 Security drop-down menu, select the appropriate WPA version for the WLAN. In Figure 20-5, WPA+WPA2 has been selected for the WLAN named devices. Under WPA+WPA2 Parameters, the WPA version has been narrowed to only WPA2 by unchecking the box next to WPA and checking both WPA2 Policy and WPA2 Encryption AES.

A screenshot of the Wireless LAN Controller GUI illustrates the selection of WPA plus WPA2 for WLAN named devices.

Figure 20-5 Selecting the WPA2 Personal Security Suite for a WLAN

For WPA2 personal mode, look under the Authentication Key Management section and check only the box next to PSK. You should then enter the pre-shared key string in the box next to PSK Format. In Figure 20-5, an ASCII text string has been entered. Be sure to click the Apply button to apply the WLAN changes you have made.

Tip

The controller allows you to enable both WPA and WPA2 check boxes. You should do that only if you have legacy clients that require WPA support and are mixed in with newer WPA2 clients. Be aware that the WLAN will only be as secure as the weakest security suite you configure on it. Ideally, you should use WPA2 or WPA3 with AES/CCMP and try to avoid any other hybrid mode. Hybrid modes such as WPA with AES and WPA2 with TKIP can cause compatibility issues; in addition, they have been deprecated.

You can verify the WLAN and its security settings from the WLANs > Edit General tab, as shown in Figure 20-6 or from the list of WLANs, as shown in Figure 20-7. In both figures, the Security Policies field is shown as [WPA2][Auth(PSK)]. You can also verify that the WLAN status is enabled and active.

A figure illustrates the verification of PSK authentication.

Figure 20-6 Verifying PSK Authentication in the WLAN Configuration

A figure illustrates checking the PSK authentication from the WLAN entries.

Figure 20-7 Verifying PSK Authentication from the List of WLANs

Authenticating with EAP

Client authentication generally involves some sort of challenge, a response, and then a decision to grant access. Behind the scenes, it can also involve an exchange of session or encryption keys, in addition to other parameters needed for client access. Each authentication method might have unique requirements as a unique way to pass information between the client and the AP.

Rather than build additional authentication methods into the 802.11 standard, Extensible Authentication Protocol (EAP) offers a more flexible and scalable authentication framework. As its name implies, EAP is extensible and does not consist of any one authentication method. Instead, EAP defines a set of common functions that actual authentication methods can use to authenticate users.

EAP has another interesting quality: It can integrate with the IEEE 802.1x port-based access control standard. When 802.1x is enabled, it limits access to a network medium until a client authenticates. This means that a wireless client might be able to associate with an AP but will not be able to pass data to any other part of the network until it successfully authenticates.

With Open Authentication and PSK authentication, wireless clients are authenticated locally at the AP without further intervention. The scenario changes with 802.1x; the client uses Open Authentication to associate with the AP, and then the actual client authentication process occurs at a dedicated authentication server. Figure 20-8 shows the three-party 802.1x arrangement, which consists of the following entities:

  • Supplicant: The client device that is requesting access

  • Authenticator: The network device that provides access to the network (usually a wireless LAN controller [WLC])

  • Authentication server (AS): The device that takes user or client credentials and permits or denies network access based on a user database and policies (usually a RADIUS server)

A figure illustrates the client authenticated by the three-party 802.1x arrangement.

Figure 20-8 802.1x Client Authentication Roles

The controller becomes a middleman in the client authentication process, controlling user access with 802.1x and communicating with the authentication server using the EAP framework.

To use EAP-based authentication and 802.1x, you should leverage the enterprise modes of WPA, WPA2, and WPA3. (As always, you should use the highest WPA version that is supported on your WLCs, APs, and wireless clients.) The enterprise mode supports many EAP methods, such as LEAP, EAP-FAST, PEAP, EAP-TLS, EAP-TTLS, and EAP-SIM, but you do not have to configure any specific method on a WLC. Instead, specific EAP methods must be configured on the authentication server and supported on the wireless client devices. Remember that the WLC acts as the EAP middleman between the clients and the AS.

Cisco WLCs can use either external RADIUS servers located somewhere on the wired network or a local EAP server located on the WLC. The following sections discuss configuration tasks for each scenario.

Configuring EAP-Based Authentication with External RADIUS Servers

You should begin by configuring one or more external RADIUS servers on the controller. Navigate to Security > AAA > RADIUS > Authentication. Click the New button to define a new server or select the Server Index number to edit an existing server definition.

In Figure 20-9, a new RADIUS server is being defined. Enter the server’s IP address and the shared secret key that the controller will use to communicate with the server. Make sure that the RADIUS port number is correct; if it isn’t, you can enter a different port number. The server status should be Enabled, as selected from the drop-down menu. You can disable a server to take it out of service if needed. To authenticate wireless clients, check the Enable box next to Network User. Click the Apply button to apply the new settings.

A screenshot of the Wireless LAN Controller GUI illustrates defining a new radius server.

Figure 20-9 Defining a RADIUS Server for WPA2 Enterprise Authentication

Next, you need to enable 802.1x authentication on the WLAN. Navigate to WLANs and select a new or existing WLAN to edit. As an example, configure the WLAN security to use WPA2 Enterprise. Under the Security > Layer 2 tab, select WPA+WPA2 and make sure that WPA2 Policy is checked and WPA Policy is not. Beside WPA2 Encryption, check the box next to AES to use the most robust encryption. Select 802.1x under the Authentication Key Management section to enable the enterprise mode. Make sure that PSK is not checked so that personal mode will remain disabled. Figure 20-10 illustrates the settings that are needed on the WLAN named staff_eap.

A screenshot of the Wireless LAN Controller GUI illustrates enabling 802.1x authentication and other settings for WLAN named staff-eap.

Figure 20-10 Enabling WPA2 Enterprise Mode with 802.1x Authentication

By default, a controller uses the global list of RADIUS servers in the order you have defined under Security > AAA > RADIUS > Authentication. You can override that list on the AAA Servers tab, where you can define which RADIUS servers will be used for 802.1x authentication. You can define up to six RADIUS servers that will be tried in sequential order, designated as Server 1, Server 2, and so on. Choose a predefined server by clicking the drop-down menu next to one of the server entries. In Figure 20-11, the RADIUS server at 192.168.10.9 will be used as Server 1. Subsequently, another RADIUS server at 192.168.10.10 is configured as Server 2. After you finish selecting servers, you can edit other WLAN parameters or click the Apply button to make your configuration changes operational.

A screenshot of the Wireless LAN Controller GUI illustrates authenticating clients by selecting RADIUS servers.

Figure 20-11 Selecting RADIUS Servers to Authenticate Clients in the WLAN

Tip

As you worked through the WPA2 enterprise configuration, did you notice that you never saw an option to use a specific authentication method, like PEAP or EAP-TLS? The controller only has to know that 802.1x will be in use. The actual authentication methods are configured on the RADIUS server. The client’s supplicant must also be configured to match what the server is using.

Configuring EAP-Based Authentication with Local EAP

If your environment is relatively small or you do not have a RADIUS server in production, you can use an authentication server that is built in to the WLC. This is called Local EAP, and it supports LEAP, EAP-FAST, PEAP, and EAP-TLS.

First, you need to define and enable the local EAP service on the controller. Navigate to Security > Local EAP > Profiles and click the New button. Enter a name for the Local EAP profile, which will be used to define the authentication server methods. In Figure 20-12, a new profile called MyLocalEAP has been defined. Click the Apply button to create the profile. Now you should see the new profile listed, along with the authentication methods it supports, as shown in Figure 20-13. From this list, you can check or uncheck the boxes to enable or disable each method.

A screenshot of the Wireless LAN Controller GUI illustrates creating a new profile on a controller.

Figure 20-12 Defining a Local EAP Profile on a Controller

A screenshot of the Wireless LAN Controller GUI shows the configured Local EAP profiles.

Figure 20-13 Displaying Configured Local EAP Profiles

Select the profile name to edit its parameters. In Figure 20-14, the profile named MyLocalEAP has been configured to use PEAP. Click the Apply button to activate your changes.

A figure illustrates configuring a profile to use PEAP.

Figure 20-14 Configuring a Local EAP Profile to Use PEAP

Next, you need to configure the WLAN to use the Local EAP server rather than a regular external RADIUS server. Navigate to WLANs, select the WLAN ID, and then select the Security > Layer 2 tab and enable WPA2, AES, and 802.1x as before.

If you have defined any RADIUS servers in the global list under Security > AAA > RADIUS > Authentication or any specific RADIUS servers in the WLAN configuration, the controller will use those first. Local EAP will then be used as a backup method.

To make Local EAP the primary authentication method, you must make sure that no RADIUS servers are defined on the controller. Select the AAA Servers tab and make sure that all three RADIUS servers use None by selecting None from the drop-down menu.

In the Local EAP Authentication section, check the Enabled box to begin using the Local EAP server. Select the EAP profile name that you have previously configured. In Figure 20-15, the Local EAP authentication server is enabled and will use the MyLocalEAP profile, which was configured for PEAP.

A screenshot displays enabling a local EAP authentication server.

Figure 20-15 Enabling Local EAP Authentication for a WLAN

Because the Local EAP server is local to the controller, you will have to maintain a local database of users or define one or more LDAP servers on the controller. You can create users by navigating to Security > AAA > Local Net Users. In Figure 20-16, a user named testuser has been defined and authorized for access to the staff_eap WLAN.

A figure illustrates defining a new user and authorizing access to staff eap WLAN.

Figure 20-16 Creating a Local User for Local EAP Authentication

Verifying EAP-Based Authentication Configuration

You can verify the WLAN and its security settings from the list of WLANs by selecting WLANs > WLAN, as shown in Figure 20-17. For EAP-based authentication, the Security Policies field should display [Auth(802.1X)]. You can also verify that the WLAN status is enabled and active.

A screenshot of the wireless LAN controller GUI illustrates the verification of EAP authentication.

Figure 20-17 Verifying EAP Authentication on a WLAN

Authenticating with WebAuth

You might have noticed that none of the authentication methods described so far involve direct interaction with the end user. For example, Open Authentication requires nothing from the user or the device. PSK authentication involves a pre-shared key that is exchanged between the device and the WLC. EAP-based authentication can present the end user with a prompt for credentials—but only if the EAP method supports it. Even so, the end user does not see any information about the network or its provider.

Web Authentication (WebAuth) is different because it presents the end user with content to read and interact with before granting access to the network. For example, it can present an acceptable use policy (AUP) that the user must accept before accessing the network. It can also prompt for user credentials, display information about the enterprise, and so on. Naturally, the user must open a web browser to see the WebAuth content. WebAuth can be used as an additional layer in concert with Open Authentication, PSK-based authentication, and EAP-based authentication.

Web Authentication can be handled locally on the WLC for smaller environments through Local Web Authentication (LWA). You can configure LWA in the following modes:

  • LWA with an internal database on the WLC

  • LWA with an external database on a RADIUS or LDAP server

  • LWA with an external redirect after authentication

  • LWA with an external splash page redirect, using an internal database on the WLC

  • LWA with passthrough, requiring user acknowledgement

When there are many controllers providing Web Authentication, it makes sense to use LWA with an external database on a RADIUS server, such as ISE, and keep the user database centralized. The next logical progression is to move the Web Authentication page onto the central server, too. This is called Central Web Authentication (CWA).

To configure WebAuth on a WLAN, first create the new WLAN and map it to the correct VLAN. Go to the General tab and enter the SSID string, apply the appropriate controller interface, and change the status to Enabled.

On the Security tab, you can select the Layer 2 tab to choose a wireless security scheme to be used on the WLAN. In Figure 20-18, the WLAN is named webauth, the SSID is Guest_webauth, and Open Authentication will be used because the None method has been selected.

A figure illustrates setting open authentication for the WLAN, WebAuth.

Figure 20-18 Configuring Open Authentication for WebAuth

Next, select the Security > Layer 3 tab and choose the Layer 3 Security type Web Policy, as shown in Figure 20-19. When the Authentication radio button is selected (the default), Web Authentication will be performed locally on the WLC by prompting the user for credentials that will be checked against RADIUS, LDAP, or local EAP servers. In the figure, Passthrough has been selected, which will display web content such as an acceptable use policy to the user and prompt for acceptance. Through the other radio buttons, WebAuth can redirect the user to an external web server for content and interaction. Click the Apply button to apply the changes to the WLAN configuration.

A figure illustrates setting layer 3 authentication for WebAuth.

Figure 20-19 Configuring WebAuth with Passthrough Authentication

You will need to configure the WLC’s local web server with content to display during a WebAuth session. Navigate to Security > Web Auth > Web Login Page, as shown in Figure 20-20. By default, internal WebAuth is used. You can enter the web content that will be displayed to the user by defining a text string to be used as the headline, as well as a block of message text.

A figure illustrates configuring page content for a WLAN.

Figure 20-20 Configuring the WebAuth Page Content

In the figure, WebAuth will display the headline “Welcome to our guest wireless!”, followed by a message requesting that the user read and accept the acceptable use policy. (An example of an AUP is not actually shown in the message.) Click the Apply button to make the WebAuth configuration active.

Figure 20-21 shows the web content that is presented to a user who attempts to connect to the WLAN. The user must click on the Accept button to be granted network access.

A web content shown by the WebAuth Passthrough authentication is shown.

Figure 20-21 Sample Web Content Presented by WebAuth Passthrough

You can verify the WebAuth security settings from the list of WLANs by selecting WLANs > WLAN. In Figure 20-22, WLAN 4 with SSID Guest_webauth is shown to use the Web-Passthrough security policy. You can also verify that the WLAN status is enabled and active.

A figure illustrates the checking of WebAuth authentication in WLAN entries.

Figure 20-22 Verifying WebAuth Authentication on a WLAN

Exam Preparation Tasks

As mentioned in the section “How to Use This Book” in the Introduction, you have a couple of choices for exam preparation: the exercises here, Chapter 30, “Final Preparation,” and the exam simulation questions in the Pearson Test Prep Software Online.

Review All Key Topics

Review the most important topics in this chapter, noted with the Key Topic icon in the outer margin of the page. Table 20-2 lists these key topics and the page number on which each is found.

Table 20-2 Key Topics for Chapter 20

Key Topic Element

Description

Page Number

Paragraph

WPA personal mode for PSK

565

List

802.1x roles

568

Paragraph

WPA enterprise mode for EAP

568

List

WebAuth modes

573

Complete Tables and Lists from Memory

There are no memory tables in this chapter.

Define Key Terms

Define the following key terms from this chapter and check your answers in the Glossary:

802.1x

authentication server (AS)

authenticator

Extensible Authentication Protocol (EAP)

Open Authentication

personal mode

RADIUS server

supplicant

Wi-Fi Protected Access (WPA)

WPA Version 2 (WPA2)

WPA Version 3 (WPA3)

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset