Information About Configuring Web-Based Authentication
Use the web-based authentication feature, known as web authentication proxy, to authenticate end users on host systems that do not run the IEEE 802.1x supplicant.
Note You can configure web-based authentication on Layer 2 interfaces.
When you initiate an HTTP session, web-based authentication intercepts ingress HTTP packets from the host and sends an HTML login page to the users. The users enter their credentials, which the web-based authentication feature sends to the authentication, authorization, and accounting (AAA) server for authentication.
If authentication succeeds, web-based authentication sends a Login-Successful HTML page to the host and applies the access policies returned by the AAA server.
If authentication fails, web-based authentication forwards a Login-Fail HTML page to the user, prompting the user to retry the login. If the user exceeds the maximum number of attempts, web-based authentication forwards a Login-Expired HTML page to the host, and the user is placed on a watch list for a waiting period.
These sections describe the role of web-based authentication as part of AAA:
With web-based authentication, the devices in the network have these specific roles:
- Client—The device (workstation) that requests access to the LAN and the services and responds to requests from the switch. The workstation must be running an HTML browser with Java Script enabled.
- Authentication server—Authenticates the client. The authentication server validates the identity of the client and notifies the switch that the client is authorized to access the LAN and the switch services or that the client is denied.
- Switch—Controls the physical access to the network based on the authentication status of the client. The switch acts as an intermediary (proxy) between the client and the authentication server, requesting identity information from the client, verifying that information with the authentication server, and relaying a response to the client.
Figure 14-1 Web-Based Authentication Device Roles
The switch maintains an IP device tracking table to store information about detected hosts.
Note By default, the IP device tracking feature is disabled on a switch. You must enable the IP device tracking feature to use web-based authentication.
For Layer 2 interfaces, web-based authentication detects IP hosts by using these mechanisms:
- ARP-based trigger—ARP redirect ACL allows web-based authentication to detect hosts with a static IP address or a dynamic IP address.
- Dynamic ARP inspection
- DHCP snooping—Web-based authentication is notified when the switch creates a DHCP-binding entry for the host.
When web-based authentication detects a new host, it creates a session as follows:
- Reviews the exception list.
If the host IP is included in the exception list, the policy from the exception list entry is applied, and the session is established.
- Reviews for authorization bypass.
If the host IP is not on the exception list, web-based authentication sends a nonresponsive-host (NRH) request to the server.
If the server response is access accepted, authorization is bypassed for this host. The session is established.
- Sets up the HTTP intercept ACL.
If the server response to the NRH request is access rejected, the HTTP intercept ACL is activated, and the session waits for HTTP traffic from the host.
When you enable web-based authentication, these events occur:
- The user initiates an HTTP session.
- The HTTP traffic is intercepted, and authorization is initiated. The switch sends the login page to the user. The user enters a username and password, and the switch sends the entries to the authentication server.
- If the authentication succeeds, the switch downloads and activates the user’s access policy from the authentication server. The login success page is sent to the user.
- If the authentication fails, the switch sends the login fail page. The user retries the login. If the maximum number of attempts fails, the switch sends the login expired page, and the host is placed in a watch list. After the watch list times out, the user can retry the authentication process.
- If the authentication server does not respond to the switch, and if an AAA fail policy is configured, the switch applies the failure access policy to the host. The login success page is sent to the user. (See the “Local Web Authentication Banner” section.)
- The switch reauthenticates a client when the host does not respond to an ARP probe on a Layer 2 interface, or when the host does not send any traffic within the idle timeout on a Layer 3 interface.
- The feature applies the downloaded timeout or the locally configured session timeout.
- If the terminate action is RADIUS, the feature sends a nonresponsive host (NRH) request to the server. The terminate action is included in the response from the server.
- If the terminate action is default, the session is dismantled, and the applied policy is removed.
Local Web Authentication Banner
You can create a banner that will appear when you log in to a switch by using web authentication.
The banner appears on both the login page and the authentication-result pop-up pages:
- Authentication Successful
- Authentication Failed
- Authentication Expired
You create a banner by using the ip admission auth-proxy-banner http global configuration command. The default banner Cisco Systems and Switch host-name Authentication appear on the Login Page. Cisco Systems appears on the authentication result pop-up page, as shown in Figure 14-2.
Figure 14-2 Authentication Successful Banner
You can also customize the banner, as shown in Figure 14-3.
- Add a switch, router, or company name to the banner by using the ip admission auth-proxy-banner http banner-text global configuration command.
- Add a logo or text file to the banner by using the ip admission auth-proxy-banner http file-path global configuration command.
Figure 14-3 Customized Web Banner
If you do not enable a banner, only the username and password dialog boxes appear in the web authentication login screen, and no banner appears when you log into the switch, as shown in Login Screen with No Banner.
Figure 14-4 Login Screen with No Banner
For more information, see the Cisco IOS Security Command Reference and the “Configuring a Web Authentication Local Banner” section.
Web Authentication Customizable Web Pages
During the web-based authentication process, the switch internal HTTP server hosts four HTML pages to deliver to an authenticating client. The server uses these pages to notify you of these four-authentication process states:
- Login—Your credentials are requested.
- Success—The login was successful.
- Fail—The login failed.
- Expire—The login session has expired because of excessive login failures.
Web Authentication Guidelines
- You can substitute your own HTML pages for the default internal HTML pages.
- You can use a logo or specify text in the login, success, failure, and expire web pages.
- On the banner page, you can specify text in the login page.
- The pages are in HTML.
- You must include an HTML redirect command in the success page to access a specific URL.
- The URL string must be a valid URL (for example, http://www.cisco.com). An incomplete URL might cause page not found error or similar errors on a web browser.
- If you configure web pages for HTTP authentication, they must include the appropriate HTML commands (for example, to set the page time out, to set a hidden password, or to confirm that the same page is not submitted twice).
- The CLI command to redirect users to a specific URL is not available when the configured login form is enabled. The administrator should ensure that the redirection is configured in the web page.
- If the CLI command redirecting users to a specific URL after authentication occurs is entered and then the command configuring web pages is entered, the CLI command redirecting users to a specific URL does not take effect.
- Configured web pages can be copied to the switch boot flash or flash.
- Configured pages can be accessed from the flash on the stack master or members.
- The login page can be on one flash, and the success and failure pages can be another flash (for example, the flash on the stack master or a member).
- You must configure all four pages.
- The banner page has no effect if it is configured with the web page.
- All of the logo files (image, flash, audio, video, and so on) that are stored in the system directory (for example, flash, disk0, or disk) and that must be displayed on the login page must use web_auth_filename as the filename.
- The configured authentication proxy feature supports both HTTP and SSL.
When configuring customized authentication proxy web pages, follow these guidelines:
- To enable the custom web pages feature, specify all four custom HTML files. If you specify fewer than four files, the internal default HTML pages are used.
- The four custom HTML files must be present on the flash memory of the switch. The maximum size of each HTML file is 8 KB.
- Any images on the custom pages must be on an accessible HTTP server. Configure an intercept ACL within the admission rule.
- Any external link from a custom page requires configuration of an intercept ACL within the admission rule.
- To access a valid DNS server, any name resolution required for external links or images requires configuration of an intercept ACL within the admission rule.
- If the custom web pages feature is enabled, a configured auth-proxy-banner is not used.
- If the custom web pages feature is enabled, the redirection URL for successful login feature is not available.
- To remove the specification of a custom file, use the no form of the command.
Because the custom login page is a public web form, consider these guidelines for the page:
- The login form must accept user entries for the username and password and must show them as uname and pwd.
- The custom login page should follow best practices for a web form, such as page timeout, hidden password, and prevention of redundant submissions.
You can substitute your HTML pages, as shown in Customizeable Authentication Page, for the default internal HTML pages. You can also specify a URL to which users are redirected after authentication occurs, which replaces the internal Success page.
Figure 14-5 Customizeable Authentication Page
Web-Based Authentication Interactions with Other Features
You can configure web-based authentication and port security on the same port. Web-based authentication authenticates the port, and port security manages network access for all MAC addresses, including that of the client. You can then limit the number or group of clients that can access the network through the port.
For more information about enabling port security, see the “Configuring Port Security” section.
LAN Port IP
You can configure LAN port IP (LPIP) and Layer 2 web-based authentication on the same port. The host is authenticated by using web-based authentication first, followed by LPIP posture validation. The LPIP host policy overrides the web-based authentication host policy.
If the web-based authentication idle timer expires, the NAC policy is removed. The host is authenticated, and posture is validated again.
You cannot configure Gateway IP (GWIP) on a Layer 3 VLAN interface if web-based authentication is configured on any of the switch ports in the VLAN.
You can configure web-based authentication on the same Layer 3 interface as Gateway IP. The host policies for both features are applied in software. The GWIP policy overrides the web-based authentication host policy.
If you configure a VLAN ACL or a Cisco IOS ACL on an interface, the ACL is applied to the host traffic only after the web-based authentication host policy is applied.
For Layer 2 web-based authentication, you must configure a port ACL (PACL) as the default access policy for ingress traffic from hosts connected to the port. After authentication, the web-based authentication host policy overrides the PACL.
Note When a proxy ACL is configured for a web-based authentication client, the proxy ACL is downloaded and applied as part of the authorization process. Hence, the PACL displays the proxy ACL access control entry (ACE).
You cannot configure a MAC ACL and web-based authentication on the same interface.
You cannot configure web-based authentication on a port whose access VLAN is configured for VACL capture.
Context-Based Access Control
Web-based authentication cannot be configured on a Layer 2 port if context-based access control (CBAC) is configured on the Layer 3 VLAN interface of the port VLAN.
You cannot configure web-based authentication on the same port as 802.1x authentication except as a fallback authentication method.
You can configure web-based authentication on a Layer 2 EtherChannel interface. The web-based authentication configuration applies to all member channels.
Default Web-Based Authentication Settings
Table 14-1 Default Web-Based Authentication Settings
- IP address
- UDP authentication port
- None specified
- None specified
Default value of inactivity timeout
Configuring Switch-to-RADIUS-Server Communication
RADIUS security servers identification:
- Host name
- Host IP address
- Host name and specific UDP port numbers
- IP address and specific UDP port numbers
The combination of the IP address and UDP port number creates a unique identifier, that enables RADIUS requests to be sent to multiple UDP ports on a server at the same IP address. If two different host entries on the same RADIUS server are configured for the same service (for example, authentication) the second host entry that is configured functions as the failover backup to the first one. The RADIUS host entries are chosen in the order that they were configured.