Cisco SRST V3.4: Setting Up the Network

This chapter describes how to configure your Cisco Survivable Remote Site Telephony (SRST) router to run DHCP and to communicate with the IP phones during Cisco CallManager fallback.

Information About Setting Up the Network

When the WAN link fails, the Cisco IP phones detect that they are no longer receiving keepalive packets from Cisco CallManager. The Cisco IP phones then register with the router. The Cisco SRST software is automatically activated and builds a local database of all Cisco IP phones attached to it (up to its configured maximum). The IP phones are configured to query the router as a backup call-processing source when the central Cisco CallManager does not acknowledge keepalive packets. The Cisco SRST router now performs call setup and processing, call maintenance, and call termination.

Cisco CallManager uses DHCP to provide Cisco IP phones with the IP address of Cisco CallManager. In a remote branch office, DHCP service is typically provided either by the SRST router itself or through the Cisco SRST router using DHCP relay. Configuring DHCP is one of two main tasks in setting up network communication. The other task is configuring the Cisco SRST router to receive messages from the Cisco IP phones through the specified IP addresses. Keepalive intervals are also set at this time.

How to Set Up the Network

Enabling IP Routing

Enabling SRST on an MGCP Gateway

To use SRST as your fallback mode with an MGCP gateway, SRST and MGCP fallback must both be configured on the same gateway. The configuration below allows SRST to assume control over the voice port and over call processing on the MGCP gateway.

Note The commands described in the configuration below are ineffective unless both commands are configured. For instance, your configuration will not work if you only configure the ccm-manager fallback-mgcp command.

Restrictions

Effective with Cisco IOS Release 12.3(14)T, the call application alternate command is replaced by the service command. The service command can be used in all releases after Cisco IOS Release 12.3(14)T. Both commands are reflected in Step 4.

SUMMARY STEPS

call application alternate [application-name]
or
service [alternate | default] service-name location

DETAILED STEPS


	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password when prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ccm-manager fallback-mgcp Example: Router(config)# ccm-manager fallback-mgcp	Enables the gateway fallback feature and allows an MGCP voice gateway to provide call processing services through SRST or other configured applications when Cisco CallManager is unavailable.
Step 4	call application alternate [application-name] or service [alternate \| default] service-name location Example: Router(config)# call application alternate or Router(config)# service default	The call application alternate command specifies that the default voice application takes over if the MGCP application is not available. The application-name argument is optional and indicates the name of the specific voice application to use if the application in the dial peer fails. If a specific application name is not entered, the gateway uses the DEFAULT application. Or The service command loads and configures a specific, standalone application on a dial peer. The keywords and arguments are as follows: •alternate—Optional. Alternate service to use if the service that is configured on the dial peer fails. •default—Optional. Specifies that the default service ("DEFAULT") on the dial peer is used if the alternate service fails. •service-name—Name that identifies the voice application. •location—Directory and filename of the Tcl script or VoiceXML document in URL format. For example, flash memory (flash:filename), a TFTP (tftp://../filename) or an HTTP server (http://../filename) are valid locations
Step 5	exit Example: Router(config)# exit	Exits global configuration mode and returns to privileged EXEC mode.

Configuring DHCP for Cisco SRST Phones

To perform this task, you must have your network configured with DHCP. For further details about DHCP configuration, see the Cisco IOS DHCP Server document and refer to your Cisco CallManager documentation.

When a Cisco IP phone is connected to the Cisco SRST system, it automatically queries for a DHCP server. The DHCP server responds by assigning an IP address to the Cisco IP phone and providing the IP address of the TFTP server through DHCP option 150. Then the phone registers with the Cisco CallManager system server and attempts to get configuration and phone firmware files from the Cisco CallManager TFTP server address provided by the DHCP server.

When setting up your network, configure your DHCP server local to your site. You may use your SRST router to provide DHCP service (recommended). If your DHCP server is across the WAN and there is an extended WAN outage, the DHCP lease times on your Cisco IP phones may expire. This may cause your phones to lose their IP addresses, resulting in a loss of service. Rebooting your phones when there is no DHCP server available after the DHCP lease has expired will not reactivate the phones, because they will be unable to obtain an IP address or other configuration information. Having your DHCP server local to your remote site ensures that the phones can continue to renew their IP address leases in the event of an extended WAN failure.

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Defining a Single DHCP IP Address Pool—Use this method if the Cisco SRST router is a DHCP server and if you can use a single shared address pool for all your DHCP clients.

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Defining the DHCP Relay Server—Use this method if the Cisco SRST router is not a DHCP server and you want to relay DHCP requests from IP phones to a DHCP server on a different router.

Defining a Single DHCP IP Address Pool

This task creates a large shared pool of IP addresses in which all DHCP clients receive the same information, including the option 150 TFTP server IP address. The benefit of selecting this method is that you set up only one DHCP pool. However, defining a single DHCP IP address pool can be a problem if some (non-IP phone) clients need to use a different TFTP server address.

SUMMARY STEPS

DETAILED STEPS


	Command or Action	Purpose
Step 6	ip dhcp pool pool-name Example: Router(config)# ip dhcp pool mypool	Creates a name for the DHCP server address pool and enters DHCP pool configuration mode.
Step 7	network ip-address [mask \| prefix-length] Example: `Router(config-dhcp)# network 10.0.0.0 255.255.0.0`	Specifies the IP address of the DHCP address pool and the optional mask or number of bits in the address prefix, preceded by a forward slash.
Step 8	option 150 ip ip-address Example: `Router(config-dhcp)# option 150 ip 10.0.22.1`	Specifies the TFTP server address from which the Cisco IP phone downloads the image configuration file. This needs to be the IP address of CallManager.
Step 9	default-router ip-address Example: `Router(config-dhcp)# default-router 10.0.0.1`	Specifies the router to which the Cisco IP phones are connected directly. •This router should be the Cisco SRST router because this is the default address that is used to obtain SRST service in the event of a WAN outage. As long as the Cisco IP phones have a connection to the Cisco SRST router, the phones are able to get the required network details.
Step 10	exit Example: Router(config-dhcp)# exit	Exits DHCP pool configuration mode.

Defining a Separate DHCP IP Address Pool for Each Cisco IP Phone

This task creates a name for the DHCP server address pool and specifies IP addresses. This method requires you to make an entry for every IP phone.

SUMMARY STEPS

DETAILED STEPS


	Command or Action	Purpose
Step 1	ip dhcp pool pool-name Example: Router(config)# ip dhcp pool pool2	Creates a name for the DHCP server address pool and enters DHCP pool configuration mode.
Step 2	host ip-address subnet-mask Example: Router(config-dhcp)# host 10.0.0.0 255.255.0.0	Specifies the IP address that you want the phone to use.
Step 3	option 150 ip ip-address Example: `Router(config-dhcp)# option 150 ip 10.0.22.1`	Specifies the TFTP server address from which the Cisco IP phone downloads the image configuration file. This needs to be the IP address of CallManager.
Step 4	default-router ip-address Example: `Router(config-dhcp)# default-router 10.0.0.1`	Specifies the router to which the Cisco IP phones are connected directly. •This router should be the Cisco SRST router because this is the default address that is used to obtain SRST service in the event of a WAN outage. As long as the Cisco IP phones have a connection to the Cisco SRST router, the phones are able to get the required network details.
Step 5	exit Example: Router(config-dhcp)# exit	Exits DHCP pool configuration mode.

Defining the DHCP Relay Server

This task sets up DHCP relay on the LAN interface where the Cisco IP phones are connected and enables the Cisco IOS DHCP server feature to relay requests from DHCP clients (phones) to a DHCP server. For further details about DHCP configuration, see the Cisco IOS DHCP Server document.

The Cisco IOS DHCP server feature is enabled on routers by default. If the DHCP server is not enabled on your Cisco SRST router, use the following steps to enable it.

SUMMARY STEPS

DETAILED STEPS


	Command or Action	Purpose
Step 1	service dhcp Example: Router(config)# service dhcp	Enables the Cisco IOS DHCP Server feature on the router.
Step 2	interface type number Example: Router(config)# interface serial 0	Enters interface configuration mode for the specified interface. See the Cisco IOS Interface and Hardware Component Command Reference, Release 12.3T for more information.
Step 3	ip helper-address ip-address Example: Router(config-if)# ip helper-address 10.0.22.1	Specifies the helper address for any unrecognized broadcast for TFTP server and Domain Name System (DNS) requests. For each server, a separate ip helper-address command is required if the servers are on different hosts. You can also configure multiple TFTP server targets by using the ip helper-address commands for multiple servers.
Step 4	exit Example: Router(config-if)# exit	Exits interface configuration mode.

Specifying Keepalive Intervals

The keepalive interval is the period of time between keepalive messages sent by a network device. A keepalive message is a message sent by one network device to inform another network device that the virtual circuit between the two is still active.

Note If you plan to use the default time interval between messages, which is 30 seconds, you do not have to perform this task.

SUMMARY STEPS

DETAILED STEPS


	Command or Action	Purpose
Step 1	call-manager-fallback Example: Router(config)# call-manager-fallback	Enters call-manager-fallback configuration mode.
Step 2	keepalive seconds Example: Router(config-cm-fallback)# keepalive 60	Sets the time interval, in seconds, between keepalive messages that are sent to the router by Cisco IP phones. •seconds—Range is 10 to 65535. Default is 30.
Step 3	exit Example: Router(config-cm-fallback)# exit	Exits call-manager-fallback configuration mode.

Example

Configuring Cisco SRST to Support Phone Functions

Tip

When the Cisco SRST is enabled, Cisco IP phones do not have to be reconfigured while in Cisco CallManager fallback mode because phones retain the same configuration that was used with Cisco CallManager.

To configure Cisco SRST on the router to support the Cisco IP phone functions, use the following commands beginning in global configuration mode.

SUMMARY STEPS

ip source-address ip-address [port port] [any-match | strict-match]

max-dn max-directory-numbers [dual-line] [preference preference-order]

DETAILED STEPS


	Command or Action	Purpose
Step 1	call-manager-fallback Example: Router(config)# call-manager-fallback	Enters call-manager-fallback configuration mode.
Step 2	ip source-address ip-address [port port] [any-match \| strict-match] Example: Router(config-cm-fallback)# ip source-address 10.6.21.4 port 2002 strict-match	Enables the router to receive messages from the Cisco IP phones through the specified IP addresses and provides for strict IP address verification. The default port number is 2000.
Step 3	max-dn max-directory-numbers [dual-line] [preference preference-order] Example: Router(config-cm-fallback)# max-dn 15 dual-line preference 1	Sets the maximum number of directory numbers (DNs) or virtual voice ports that can be supported by the router and activates the dual-line mode. •max-directory-numbers—Maximum number of directory numbers or virtual voice ports supported by the router. The maximum number is platform-dependent. The default is 0. See the "Platform and Memory Support" section on page 24 for further details. •dual-line—(Optional) Allows IP phones in Cisco CallManager fallback mode to have a virtual voice port with two channels. •preference preference-order (Optional)—Sets the global preference for creating the VoIP dial peers for all directory numbers that are associated with the primary number. Range is from 0 to 10. Default is 0, which is the highest preference. The alias command also has a preference keyword that sets alias command preference values. Setting the alias command preference keyword allows the default preference set with the max-dn command to be overriden. See Configuring Call Rerouting, page 58 for more information on using the max-dn command with the alias command. Note You must reboot the router in order to reduce the limit of the directory numbers or virtual voice ports after the maximum allowable number is configured.
Step 4	max-ephones max-phones Example: `Router(config-cm-fallback)# max-ephones 24`	Configures the maximum number of Cisco IP phones that can be supported by the router. The default is 0. The maximum number is platform dependent. See the "Platform and Memory Support" section on page 24 for further details. Note You must reboot the router in order to reduce the limit of Cisco IP phones after the maximum allowable number is configured.
Step 5	limit-dn {7910 \| 7935 \| 7940 \| 7960} max-lines Example: `Router(config-cm-fallback)# limit-dn 7910 2`	Limits the directory number lines on Cisco IP phones during Cisco CallManager fallback. Note You must configure this command during initial Cisco SRST router configuration, before any phone actually registers with the Cisco SRST router. However, you can modify the number of lines at a later time. The setting for maximum lines is from 1 to 6. The default number of maximum directory lines is set to 6. If there is any active phone with the last line number greater than this limit, warning information is displayed for phone reset.
Step 6	exit Example: `Router(config-cm-fallback)# exit`	Exits call-manager-fallback configuration mode.

Verifying That Cisco SRST Is Enabled

Step 1

Enter the show running-config command to verify the configuration.

Step 2

Enter the show call-manager-fallback all command to verify that the Cisco SRST feature is enabled.

Step 3

Use the Settings display on the Cisco IP phones in your network to verify that the default router IP address on the phones matches the IP address of the Cisco SRST router.

Step 4

To temporarily block the TCP port 2000 Skinny Client Control Protocol (SCCP) connection for one of the Cisco IP phones in order to force the Cisco IP phone to lose its connection to the Cisco CallManager and register with the Cisco SRST router, perform the following steps:

Use the appropriate IP access-list command to temporarily disconnect a Cisco IP phone from the Cisco CallManager.

During a WAN connection failure, when Cisco SRST is enabled, Cisco IP phones display a message informing you that they are operating in Cisco CallManager fallback mode. The Cisco IP Phone 7960 and Cisco IP Phone 7940 display a "CM Fallback Service Operating" message, and the Cisco IP Phone 7910 displays a "CM Fallback Service" message when operating in Cisco CallManager fallback mode. When the Cisco CallManager is restored, the message goes away and full Cisco IP phone functionality is restored.

Enter the no form of the appropriate access-list command to restore normal service for the phone.

Use the debug ephone register command to observe the registration process of the Cisco IP phone on the Cisco SRST router.

Use the show ephone command to display the Cisco IP phones that have registered to the Cisco SRST router.

Troubleshooting

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To set keepalive debugging for Cisco IP phones, use the debug ephone keepalive command.

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To set registration debugging for Cisco IP phones, use the debug ephone register command.

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To set state debugging for Cisco IP phones, use the debug ephone state command.

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To set detail debugging for Cisco IP phones, use the debug ephone detail command.

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To set error debugging for Cisco IP phones, use the debug ephone error command.

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To set call statistics debugging for Cisco IP phones, use the debug ephone statistics command.

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To provide voice-packet-level debugging and to display the contents of one voice packet in every 1024 voice packets, use the debug ephone pak command.

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To provide raw low-level protocol debugging display for all SCCP messages, use the debug ephone raw command.

Where to Go Next

The next step is setting up the phone and getting a dial tone. For instructions, see the " Setting Up Cisco IP Phones" chapter.

Table Of Contents

Setting Up the Network

Contents

Information About Setting Up the Network

How to Set Up the Network

Enabling IP Routing

Enabling SRST on an MGCP Gateway

Restrictions

SUMMARY STEPS

DETAILED STEPS

Configuring DHCP for Cisco SRST Phones

Defining a Single DHCP IP Address Pool

SUMMARY STEPS

DETAILED STEPS

Defining a Separate DHCP IP Address Pool for Each Cisco IP Phone

SUMMARY STEPS

DETAILED STEPS

Defining the DHCP Relay Server

SUMMARY STEPS

DETAILED STEPS

Specifying Keepalive Intervals

SUMMARY STEPS

DETAILED STEPS

Example

Configuring Cisco SRST to Support Phone Functions

SUMMARY STEPS

DETAILED STEPS

Verifying That Cisco SRST Is Enabled

Troubleshooting

Where to Go Next