Catalyst 3750-X and 3560-X Switch Software Configuration Guide, Release 12.2(53)SE2

Device Roles

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 12-1 shows the roles of these devices in a network:

Figure 12-1 Web-Based Authentication Device Roles

Host Detection

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.

Session Creation

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.

Authentication Process

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 12-2.

Figure 12-2 Authentication Successful Banner

You can also customize the banner, as shown in Figure 12-3.

• 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 12-3 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 12-4 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.

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 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 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.
• On stackable switches, 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 file name.
• The configured authentication proxy feature supports both HTTP and SSL.

You can substitute your HTML pages, as shown inFigure 12-5, 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 12-5 Customizeable Authentication Page

For more information, see the “Customizing the Authentication Proxy Web Pages” section.

Web-based Authentication Interactions with Other Features

• Port Security
• LAN Port IP
• Gateway IP
• ACLs
• Context-Based Access Control
• 802.1x Authentication
• EtherChannel

Port Security

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.

Gateway IP

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.

ACLs

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.

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.

802.1x Authentication

You cannot configure web-based authentication on the same port as 802.1x authentication except as a fallback authentication method.

EtherChannel

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 Configuration

Table 12-1 shows the default web-based authentication configuration.

Web-Based Authentication Configuration Guidelines and Restrictions

• Web-based authentication is an ingress-only feature.
• You can configure web-based authentication only on access ports. Web-based authentication is not supported on trunk ports, EtherChannel member ports, or dynamic trunk ports.
• You must configure the default ACL on the interface before configuring web-based authentication. Configure a port ACL for a Layer 2 interface or a Cisco IOS ACL for a Layer 3 interface.
• You cannot authenticate hosts on Layer 2 interfaces with static ARP cache assignment. These hosts are not detected by the web-based authentication feature because they do not send ARP messages.
• 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.
• You must configure at least one IP address to run the switch HTTP server. You must also configure routes to reach each host IP address. The HTTP server sends the HTTP login page to the host.
• Hosts that are more than one hop away might experience traffic disruption if an STP topology change results in the host traffic arriving on a different port. This occurs because the ARP and DHCP updates might not be sent after a Layer 2 (STP) topology change.
• Web-based authentication does not support VLAN assignment as a downloadable-host policy.
• Web-based authentication is not supported for IPv6 traffic.

Web-Based Authentication Configuration Task List

• Configuring the Authentication Rule and Interfaces
• Configuring AAA Authentication
• Configuring Switch-to-RADIUS-Server Communication
• Configuring the HTTP Server
• Configuring an AAA Fail Policy
• Configuring the Web-Based Authentication Parameters
• Removing Web-Based Authentication Cache Entries

Configuring the Authentication Rule and Interfaces

This example shows how to enable web-based authentication on Fast Ethernet port 5/1:

This example shows how to verify the configuration:

Configuring AAA Authentication

This example shows how to enable AAA:

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.

To configure the RADIUS server parameters, perform this task:

When you configure the RADIUS server parameters:

• Specify the key string on a separate command line.
• For key string , specify the authentication and encryption key used between the switch and the RADIUS daemon running on the RADIUS server. The key is a text string that must match the encryption key used on the RADIUS server.
• When you specify the key string, use spaces within and at the end of the key. If you use spaces in the key, do not enclose the key in quotation marks unless the quotation marks are part of the key. This key must match the encryption used on the RADIUS daemon.
• You can globally configure the timeout, retransmission, and encryption key values for all RADIUS servers by using with the radius-server host global configuration command. If you want to configure these options on a per-server basis, use the radius-server timeout, radius-server retransmit, and the radius-server key global configuration commands. For more information, see the
  Cisco IOS Security Configuration Guide, Release 12.2 and the
  Cisco IOS Security Command Reference, Release 12.2 at this URL:

http://www.cisco.com/en/US/docs/ios/12_2/security/command/reference/fsecur_r.html

Note You need to configure some settings on the RADIUS server, including: the switch IP address, the key string to be shared by both the server and the switch, and the downloadable ACL (DACL). For more information, see the RADIUS server documentation.

This example shows how to configure the RADIUS server parameters on a switch:

Configuring the HTTP Server

To use web-based authentication, you must enable the HTTP server within the switch. You can enable the server for either HTTP or HTTPS.

You can configure custom authentication proxy web pages or specify a redirection URL for successful login.

Note To ensure secure authentication when you enter the ip http secure-secure command, the login page is always in HTTPS (secure HTTP) even if the user sends an HTTP request.

• Customizing the Authentication Proxy Web Pages
• Specifying a Redirection URL for Successful Login

Customizing the Authentication Proxy Web Pages

You can configure web authentication to display four substitute HTML pages to the user in place of the switch default HTML pages during web-based authentication.

To specify the use of your custom authentication proxy web pages, first store your custom HTML files on the switch flash memory, then perform this task in global configuration mode:

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.
• T o 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.

This example shows how to configure custom authentication proxy web pages:

This example shows how to verify the configuration of a custom authentication proxy web pages:

Specifying a Redirection URL for Successful Login

You can specify a URL to which the user is redirected after authentication, effectively replacing the internal Success HTML page.

When configuring a redirection URL for successful login, consider these guidelines:

• If the custom authentication proxy web pages feature is enabled, the redirection URL feature is disabled and is not available in the CLI. You can perform redirection in the custom-login success page.
• If the redirection URL feature is enabled, a configured auth-proxy-banner is not used.
• To remove the specification of a redirection URL, use the no form of the command.

This example shows how to configure a redirection URL for successful login:

This example shows how to verify the redirection URL for successful login:

Configuring an AAA Fail Policy

This example shows how to apply an AAA failure policy:

This example shows how to determine whether any connected hosts are in the AAA Down state:

This example shows how to view detailed information about a particular session based on the host IP address:

Configuring the Web-Based Authentication Parameters

You can configure the maximum number of failed login attempts before the client is placed in a watch list for a waiting period.

This example shows how to set the maximum number of failed login attempts to 10:

Configuring a Web Authentication Local Banner

Beginning in privileged EXEC mode, follow these steps to configure a local banner on a switch that has web authentication configured.

This example shows how to configure a local banner with the custom message My Switch:

For more information about the ip auth-proxy auth-proxy-banner command, see the “Authentication Proxy Commands” section of the Cisco IOS Security Command Reference on Cisco.com.

Removing Web-Based Authentication Cache Entries

This example shows how to remove the web-based authentication session for the client at the IP address 209.165.201.1: