Clientless SSL VPN Troubleshooting

December 15, 2014

Closing Application Access to Prevent hosts File Errors

To prevent hosts file errors that can interfere with Application Access, close the Application Access window properly when you finish using Application Access. To do so, click the close icon.

Recovering from Hosts File Errors When Using Application Access

The following errors can occur if you do not close the Application Access window properly:

  • The next time you try to start Application Access, it may be switched off; you receive a Backup HOSTS File Found error message.
  • The applications themselves may be switched off or malfunction, even when you are running them locally.

These errors can result from terminating the Application Access window in any improper way. For example:

  • Your browser crashes while you are using Application Access.
  • A power outage or system shutdown occurs while you are using Application Access.
  • You minimize the Application Access window while you are working, then shut down your computer with the window active (but minimized).

This section includes the following topics:

Understanding the hosts File

The hosts file on your local system maps IP addresses to hostnames. When you start Application Access, Clientless SSL VPN modifies the hosts file, adding Clientless SSL VPN-specific entries. Stopping Application Access by properly closing the Application Access window returns the file to its original state.

 

Before invoking Application Access...

hosts file is in original state.

When Application Access starts....
  • Clientless SSL VPN copies the hosts file to hosts.webvpn, thus creating a backup.
  • Clientless SSL VPN then edits the hosts file, inserting Clientless SSL VPN-specific information.

When Application Access stops...
  • Clientless SSL VPN copies the backup file to the hosts file, thus restoring the hosts file to its original state.
  • Clientless SSL VPN deletes hosts.webvpn.

After finishing Application Access...

hosts file is in original state.

Note Microsoft anti-spyware software blocks changes that the port forwarding Java applet makes to the hosts file. See www.microsoft.com for information on how to allow hosts file changes when using anti-spyware software.

Stopping Application Access Improperly

When Application Access terminates abnormally, the hosts file remains in a Clientless SSL VPN-customized state. Clientless SSL VPN checks the state the next time you start Application Access by searching for a hosts.webvpn file. If it finds one, a Backup HOSTS File Found error message (Figure 18-1) appears, and Application Access is temporarily switched off.

Once you shut down Application Access improperly, you leave your remote access client/server applications in limbo. If you try to start these applications without using Clientless SSL VPN, they may malfunction. You may find that hosts that you normally connect to are unavailable. This situation could commonly occur if you run applications remotely from home, fail to quit the Application Access window before shutting down the computer, then try to run the applications later from the office.

Reconfiguring a Host’s File Automatically Using Clientless SSL VPN

If you are able to connect to your remote access server, follow these steps to reconfigure the host’s file and re-enable both Application Access and the applications.

DETAILED STEPS

Step 1 Start Clientless SSL VPN and log in. The home page opens.

Step 2 Click the Applications Access link. A Backup HOSTS File Found message appears. (See Figure 18-1.)

Figure 18-1 Backup HOSTS File Found Message

 

Step 3 Choose one of the following options:

    • Restore from backup —Clientless SSL VPN forces a proper shutdown. It copies the hosts.webvpn backup file to the hosts file, restoring it to its original state, then deletes hosts.webvpn. You then have to restart Application Access.
    • Do nothing —Application Access does not start. The remote access home page reappears.
    • Delete backup —Clientless SSL VPN deletes the hosts.webvpn file, leaving the hosts file in its Clientless SSL VPN-customized state. The original hosts file settings are lost. Application Access then starts, using the Clientless SSL VPN-customized hosts file as the new original. Choose this option only if you are unconcerned about losing hosts file settings. If you or a program you use may have edited the hosts file after Application Access has shut down improperly, choose one of the other options, or edit the hosts file manually. (See “Reconfiguring hosts File Manually.”)

 

Reconfiguring hosts File Manually

If you are not able to connect to your remote access server from your current location, or if you have customized the hosts file and do not want to lose your edits, follow these steps to reconfigure the hosts file and reenable both Application Access and the applications.

DETAILED STEPS

Step 1 Locate and edit your hosts file. The most common location is c:\windows\sysem32\drivers\etc\hosts.

Step 2 Check to see if any lines contain the string: # added by WebVpnPortForward
If any lines contain this string, your hosts file is Clientless SSL VPN-customized. If your hosts file is Clientless SSL VPN-customized, it looks similar to the following example:

server1 # added by WebVpnPortForward
server1.example.com invalid.cisco.com # added by WebVpnPortForward
server2 # added by WebVpnPortForward
server2.example.com invalid.cisco.com # added by WebVpnPortForward
server3 # added by WebVpnPortForward
server3.example.com invalid.cisco.com # added by WebVpnPortForward
 
# Copyright (c) 1993-1999 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to hostnames. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding hostname.
# The IP address and the hostname should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
# 102.54.94.97 cisco.example.com # source server
# 38.25.63.10 x.example.com # x client host
 
127.0.0.1 localhost
 
 

Step 3 Delete the lines that contain the string: # added by WebVpnPortForward

Step 4 Save and close the file.

Step 5 Start Clientless SSL VPN and log in.

The home page appears.

Step 6 Click the Application Access link.

The Application Access window appears. Application Access is now enabled.

Sending an Administrator’s Alert to Clientless SSL VPN Users

Step 1 In the main ASDM application window, choose Tools > Administrator’s Alert Message to Clientless SSL VPN Users.

The Administrator’s Alert Message to Clientless SSL VPN Users dialog box appears.

Step 2 Enter the new or edited alert content to send, and then click Post Alert.

Step 3 To remove current alert content and enter new alert content, click Cancel Alert.

Sending an Administrator’s Alert to Clientless SSL VPN Users

Step 1 In the main ASDM application window, choose Tools > Administrator’s Alert Message to Clientless SSL VPN Users.

The Administrator’s Alert Message to Clientless SSL VPN Users dialog box appears.

Step 2 Enter the new or edited alert content to send, and then click Post Alert.

Step 3 To remove current alert content and enter new alert content, click Cancel Alert.

 

Protecting Clientless SSL VPN Session Cookies

Embedded objects such as Flash applications and Java applets, as well as external applications, usually rely on an existing session cookie to work with the server. They get it from a browser using some Javascript on initialization. Adding the httponly flag to the Clientless SSL VPN session cookie will make the session cookie only visible to the browser, not the client-side scripts, and it makes session sharing impossible.

Prerequisites

Change the VPN session cookie setting only when there are no active Clientless SSL VPN sessions Use the show vpn-sessiondb webvpn command to check the status of Clientless SSL VPN sessions. Use the vpn-sessiondb logoff webvpn command to log out of all Clientless SSL VPN sessions.

Guidelines

The following Clientless SSL VPN features will not work when the http-only-cookie command is enabled:

  • Java plug-ins
  • Java rewriter
  • Port forwarding
  • File browser
  • Sharepoint features that require desktop applications (for example, MS Office applications)
  • AnyConnect Web launch
  • Citrix Receiver, XenDesktop, and Xenon
  • Other non-browser-based and browser plugin-based applications

To prevent a Clientless SSL VPN session cookie from being accessed by a third party through a client-side script such as Javascript, perform the following steps:

 

Step 1 Choose Configuration > Remote Access VPN > Clientless SSL VPN Access > Advanced > HTTP Cookie.

Step 2 Check the Enable HTTP-only VPN cookies check box.

Note Use this setting only if Cisco TAC advises you to do so. Enabling this command presents a security risk because the Clientless SSL VPN features listed under the Guidelines section will not work without any warning.

Step 3 Click Apply to save your changes.