Cisco Unified CallManager Security Guide, Release 5.0(2)
Configuring a Secure Survivable Remote Site Telephony (SRST) Reference
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Configuring a Secure Survivable Remote Site Telephony (SRST) Reference

Table Of Contents

Configuring a Secure Survivable Remote Site Telephony (SRST) Reference

Overview for Securing the SRST

Secure SRST Configuration Checklist

Configuring Secure SRST References

Security Configuration Settings for SRST References

Troubleshooting Secure SRST References

Deleting Security from the SRST Reference

Security Message That Displays During SRST Reference Configuration

Troubleshooting When the SRST Certificate Is Deleted from the Gateway

Where to Find More Information


Configuring a Secure Survivable Remote Site Telephony (SRST) Reference


This chapter contains information on the following topics:

Overview for Securing the SRST

Secure SRST Configuration Checklist

Configuring Secure SRST References

Security Configuration Settings for SRST References

Troubleshooting Secure SRST References

Where to Find More Information

Overview for Securing the SRST

A SRST-enabled gateway provides limited call-processing tasks if the Cisco Unified CallManager cannot complete the call. Secure SRST-enabled gateways contain a self-signed certificate. After you perform SRST configuration tasks in Cisco Unified CallManager Administration, Cisco Unified CallManager uses a TLS connection to authenticate with the Certificate Provider service in the SRST-enabled gateway. Cisco Unified CallManager then retrieves the certificate from the SRST-enabled gateway and adds the certificate to the Cisco Unified CallManager database.

After you reset the dependent devices in Cisco Unified CallManager Administration, the TFTP server adds the SRST-enabled gateway certificate to the phone cnf.xml file and sends the file to the phone. A secure phone then uses a TLS connection to interact with the SRST-enabled gateway.


Tip The phone configuration file only contains a certificate from a single issuer. Consequently, the system does not support HSRP.


Ensure that the following criteria are met, so the TLS handshake occurs between the secure phone and the SRST-enabled gateway:

The SRST reference contains a self-signed certificate.

You configured the cluster for secure mode through the Cisco CTL client.

You configured the phone for authentication or encryption.

You configured the SRST reference in Cisco Unified CallManager Administration.

You reset the SRST-enabled gateway and the dependent phones after the SRST configuration.

When the cluster security mode equals nonsecure, the device security mode remains nonsecure in the phone configuration file, even though Cisco Unified CallManager Administration may indicate that the device security mode is authenticated or encrypted. Under these circumstances, the phone attempts nonsecure connections with the SRST-enabled gateway and the Cisco Unified CallManager servers in the cluster.

When the cluster security mode equals nonsecure, the system ignores the security-related configuration in Cisco Unified CallManager Administration; for example, the device security mode, the IS SRST Secure? check box, and so on. The configuration does not get deleted in Cisco Unified CallManager Administration, but security is not provided.

The phone attempts a secure connection to the SRST-enabled gateway only when the cluster security mode equals Secure Mode, the device security mode in the phone configuration file is set to authenticated or encrypted, the Is SRST Secure? check box is checked in the SRST Configuration window, and a valid SRST-enabled gateway certificate exists in the phone configuration file.


Tip If you configured secure SRST references in a previous Cisco Unified CallManager release, the configuration automatically migrates during the Cisco Unified CallManager upgrade.



Note If phones in encrypted or authenticated mode fail over to SRST, and, during the connection with SRST, the Cisco Unified CallManager cluster switches from secure mode to nonsecure mode, these phones will not fall back to Cisco Unified CallManager automatically. Administrators must power down the SRST router to force these phones to reregister to Cisco Unified CallManager. After phones fall back to Cisco Unified CallManager, administrators can power up SRST and failover and fallback will be automatic again.


Secure SRST Configuration Checklist

Use Table 12-1 to guide you through the SRST configuration process for security.

Table 12-1 Configuration Checklist for Securing the SRST 

Configuration Steps
Related Procedures and Topics

Step 1 

Verify that you performed all necessary tasks on the SRST-enabled gateway, so the device supports Cisco Unified CallManager and security.

Cisco IOS SRST Version 3.3 System Administrator Guide that supports this version of Cisco Unified CallManager, which you can obtain at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/voice/srst/srst33/srst33ad/index.htm

Step 2 

Verify that you performed all necessary tasks to install and configure the Cisco CTL client.

Configuring the Cisco CTL Client

Step 3 

Verify that a certificate exists in the phone.

Refer to the Cisco Unified IP Phone documentation for your phone model.

Step 4 

Verify that you configured the phones for authentication or encryption.

Applying a SCCP or SIP Phone Security Profile

Step 5 

In Cisco Unified CallManager Administration, configure the SRST reference for security, which includes enabling the SRST reference in the Device Pool Configuration window.

Configuring Secure SRST References

Step 6 

Reset the SRST-enabled gateway and phones.

Configuring Secure SRST References

Configuring Secure SRST References

Consider the following information before you add, update, or delete the SRST reference in Cisco Unified CallManager Administration:

Adding a Secure SRST Reference—The first time that you configure the SRST reference for security, you must configure all settings that are described in Table 12-2.

Updating a Secure SRST Reference—Performing SRST updates in Cisco Unified CallManager Administration does not automatically update the SRST-enabled gateway certificate. To update the certificate, you must click the Update Certificate button; after you click the button, the contents of the certificate display, and you must accept or reject the certificate. If you accept the certificate, Cisco Unified CallManager replaces the SRST-enabled gateway certificate in the trust folder on each server in the cluster.

Deleting a Secure SRST Reference—Deleting a secure SRST reference removes the SRST-enabled gateway certificate from the Cisco Unified CallManager database and the cnf.xml file in the phone.

For information on how to delete SRST references, refer to the Cisco Unified CallManager Administration Guide.

To configure a secure SRST reference, perform the following procedure:

Procedure


Step 1 In Cisco Unified CallManager Administration, choose System > SRST.

Step 2 Perform one of the following tasks:

To add a new SRST reference, click the Add New button and continue with Step 3.

To copy an existing SRST reference, locate the appropriate SRST reference as described in the Cisco Unified CallManager Administration Guide, click the Copy button next to the reference that you want to copy and continue with Step 3.

To update an existing SRST reference, locate the appropriate SRST reference as described in the Cisco Unified CallManager Administration Guide and continue with Step 3.

Step 3 Enter the security-related settings as described in Table 12-2.

For descriptions of additional SRST reference configuration settings, refer to the Cisco Unified CallManager Administration Guide.

Step 4 After you check the Is SRST Secure? check box, a dialog box displays a message that you must download the SRST certificate by clicking the Update Certificate button. Click OK.

Step 5 Click Save.

Step 6 To update the SRST-enabled gateway certificate in the database, click the Update Certificate button.


Tip This button displays only after you check the Is SRST Secure? check box and click Save.


Step 7 The fingerprint for the certificate displays. To accept the certificate, click Save.

Step 8 Click Close.

Step 9 In the SRST Reference Configuration window, click Reset.


Additional Steps

Verify that you enabled the SRST reference in the Device Pool Configuration window.

Additional Information

See the "Related Topics" section.

Security Configuration Settings for SRST References

Table 12-2 describes the available settings for secure SRST references in Cisco Unified CallManager Administration.

Table 12-2 Configuration Settings for Secure SRST References 

Setting
Description

Is SRST Secure?

After you verify that the SRST-enabled gateway contains a self-signed certificate, check this check box.

After you configure the SRST and reset the gateway and dependent phones, the Cisco CTL Provider service authenticates to the Certificate Provider service on the SRST-enabled gateway. The Cisco CTL client retrieves the certificate from the SRST-enabled gateway and stores the certificate in the Cisco Unified CallManager database.

Tip To remove the SRST certificate from the database and phone, uncheck this check box, click Save, and reset the dependent phones.

SRST Certificate Provider Port

This port monitors requests for the Certificate Provider service on the SRST-enabled gateway. Cisco Unified CallManager uses this port to retrieve the certificate from the SRST-enabled gateway. The Cisco SRST Certificate Provider default port equals 2445.

After you configure this port on the SRST-enabled gateway, enter the port number in this field.

Tip You may need to configure a different port number if the port is currently used or if you use a firewall and you cannot use the port within the firewall.

Update Certificate


Tip This button displays only after you check the Is SRST Secure? check box and click Save.


After you click this button, the Cisco CTL client replaces the existing SRST-enabled gateway certificate that is stored in the Cisco Unified CallManager database, if a certificate exists in the database. After you reset the dependent phones, the TFTP server sends the cnf.xml file (with the new SRST-enabled gateway certificate) to the phones.


Troubleshooting Secure SRST References

This section contains information on the following topics:

Deleting Security from the SRST Reference

Security Message That Displays During SRST Reference Configuration

Troubleshooting When the SRST Certificate Is Deleted from the Gateway

Deleting Security from the SRST Reference

To make the SRST reference nonsecure after you configure security, uncheck the Is the SRTS Secure? check box in the SRST Configuration window in Cisco Unified CallManager Administration. A message states that you must turn off the credential service on the gateway.

Security Message That Displays During SRST Reference Configuration

The following message may display when you configure secure SRST references in Cisco Unified CallManager Administration: "Port Numbers can only contain digits."

This message displays if you enter an invalid port number when you configure the SRST Certificate Provider Port. The port number must exist in the range of 1024 and 49151.

Troubleshooting When the SRST Certificate Is Deleted from the Gateway

If the SRST certificate no longer exists in the SRST-enabled gateway, you must remove the SRST certificate from the Cisco Unified CallManager database and the phone.

To perform this task, uncheck the Is the SRST Secure? check box and click Update in the SRST Configuration window; then, click Reset Devices.

Where to Find More Information

Related Topics

Overview for Securing the SRST

Secure SRST Configuration Checklist

Configuring Secure SRST References

Security Configuration Settings for SRST References

Troubleshooting Secure SRST References

Related Cisco Documentation

Cisco IOS SRST Version 3.3 System Administrator Guide

Cisco Unified CallManager Administration Guide