Table Of Contents

Network Scenarios

Cisco 827 Router Network Connections

Cisco 831 Router Virtual Private Network Connections

Cisco 836 or Cisco SOHO 96 Network Connection

Cisco 837 Router Network Connections

Internet Access Scenarios

Before You Configure Your Internet Access Network

Replacing a Bridge or Modem with a Cisco 827 Router

Configuring the Scenario

Configuration Example

PPP over Ethernet with NAT

Configuring the Virtual Private Dial-Up Network Group Number

Configuring the ATM Interface

Configuring the Dialer Interface

Configuration Example

PPP over Ethernet with NAT Using a Dial-on-Demand PPP-over- Ethernet Connection

Configuring the Virtual Private Dial-Up Network Group Number

Configuring the ATM Interface

Configuring the Dialer Interface

Configuration Example

PPP over ATM with NAT

Configuring the Ethernet interface

Configuring the Dialer Interface

Configuring the ATM Interface

Configuring NAT

Configuration Example

Configuring Dial Backup

Dial Backup Feature Limitations and Configuration

Cisco 836 and Cisco 837 Routers and Cisco SOHO 96 and Cisco SOHO 97 Routers

Cisco 831 and Cisco SOHO 91 Routers

Configuring Dial Backup and Remote Management for the Cisco 837 and Cisco SOHO 97 Routers

Configuring Dial Backup and Remote Management for the Cisco 836 and Cisco SOHO 96 Routers

PPP over ATM with Centrally Managed Addressing and with Dial Backup

Configuring Dial Backup and Remote Management for the Cisco 837 Router

Configuration Example

Configuring Dial Backup and Remote Management for the Cisco 836 Router

Configuring the Cisco 836 Router's ISDN Settings

Configuring Dial Backup and Remote Management Settings

Configuring Backup Interface

Configuring Floating Static Route

Configuring Dialer Watch

Configuration Example

Configuring the Aggregator and ISDN Peer Router

Configuring Remote Management for the Cisco SOHO 97 Router

Configuration Example

Configuring Dial Backup and Remote Management for Cisco 831 Router and Cisco SOHO 91 Router

Configuration Example for the Cisco 831 Router

Configuring Remote Management for the Cisco SOHO 91 Router

Configuration Example

Configuring the DHCP Server

Configuring the Ethernet Interface

Dynamic Addressing Received via IPCP

Configuring the Central Cisco 3620

Configuring the Central RADIUS Server

RFC 1483 Encapsulation with NAT

Configuring the Ethernet Interface

Configuring the ATM Interface

Configuring NAT

Configuration Examples

Integrated Routing and Bridging

Configuring the Default Gateway

Configuring the Ethernet Interface and IRB

Configuring the ATM Interface

Configuring the BVI

Configuring NAT

Configuration Example

Concurrent Routing and Bridging

Specifying CRB and Configuring the Ethernet Interface

Configuring the ATM Interface and Subinterfaces

Configuring Voice Ports

Configuring the POTS Dial Peers

Configuring VoIP Dial Peers for H.323 Signaling

Configuration Example

Voice Scenario

Data Network

Voice Network

Configuration Tasks

Configuring the Class Map, Route Map, and Policy Map

Configuring the Ethernet Interface

Configuring the ATM Interface

Configuring Enhanced IGRP

Configuring the POTS Dial Peers

Configuring VoIP Dial Peers for H.323 Signaling

Configuration Examples

Cisco 827-4V Router Configuration Example

Cisco 3640 Gateway Configuration Example

Cisco 3640 Gatekeeper Configuration Example

Network Scenarios

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This chapter includes some example network scenarios and their configurations using Cisco 827 and Cisco 827-4V routers and Cisco 831, Cisco 836, Cisco 837, Cisco SOHO 91, Cisco SOHO 96, and Cisco SOHO 97 routers. This chapter is useful if you are building a new network and want some guidance. Most of the lessons here can be applied as well to networks incorporating Cisco 826, Cisco 828, Cisco SOHO 76, Cisco SOHO 77, and/or Cisco SOHO 78 routers.

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Note To verify that a feature is compatible with your router, you can use the software advisor too.

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If you already have a network set up and you want to add specific features, see "Basic Router Configuration" and "Advanced Router Configuration."

The following sections are included in this chapter:

•Cisco 827 Router Network Connections

•Cisco 831 Router Virtual Private Network Connections

•Cisco 836 or Cisco SOHO 96 Network Connection

•Cisco 837 Router Network Connections

•Internet Access Scenarios

•Configuring Dial Backup

•Configuring the DHCP Server

•Voice Scenario

Each scenario in this chapter is described with a network diagram and configuration network examples are provided as models after which you can pattern your network. They cannot, however, anticipate all of your network needs. You can choose not to use features presented in the examples or to add or substitute features that better suit your needs.

Cisco 827 Router Network Connections

Figure 2-1 illustrates an example network topology employing Cisco 827 routers connecting to the following:

•Public switched telephone network (PSTN)

•Corporate intranet

•Service provider on the Internet

•Service provider data center

Figure 2-1 Cisco 827 Routers Network Connections

1	Corporate network connecting through a Cisco 3640 voice gateway	4	Data and voice local exchange carrier connecting through a Cisco MGX voice gateway
2	Wholesale ISP business	5	Small business or remote user, connecting to the network through a Cisco 827/827-4V router
3	ISP POP (data center) with video conferencing MCUs and IP/TV video servers

In the example, Cisco 827 routers send data or voice packets from the remote user to the service provider or corporate network through a high-speed, point-to-multi-point asymmetric digital subscriber line (ADSL) technology.

Cisco 831 Router Virtual Private Network Connections

Figure 2-2 shows how a Cisco 831 router can be used in a Virtual Private Network (VPN). The Cisco 831 router is linked to the ISP via a digital subscriber line (DSL) or a cable modem. Security is provided via IP security (IPSec) configuration.

Figure 2-2 Cisco 831 Router Virtual Private Network

1	Small business or remote user, connecting to the network through a Cisco 831 router.	3	Dial backup, as a failover link when primary line goes down
2	Corporate network connecting through a Cisco router	4	Branch office network connecting through a Cisco router

Cisco 836 or Cisco SOHO 96 Network Connection

Figure 2-3 shows an example of a network topology employing a Cisco 836 router or a Cisco SOHO 96 router connecting to the following:

•ISDN

•Corporate intranet

•Service provider on the Internet

•Service provider data center

•Dial backup and remote management

Figure 2-3 Cisco 836 Router Network Connections

1	Corporate network connecting through a Cisco 3640 gateway	4	Dial backup or remote management that keeps the traffic working in case of primary line shutdown
2	Wholesale ISP business	5	ISDN to serve as an interface for dial backup or remote management
3	ISP POP (data center) with videoconferencing MCUs and IP/TV video servers	6	Small business or remote user, connecting to the network through a Cisco 836 router

Cisco 837 Router Network Connections

Figure 2-4 shows an example of a network topology employing a Cisco 837 router connecting to the following:

•PSTN

•Corporate intranet

•Service provider on the Internet

•Service provider data center

•Dial backup and remote management

Figure 2-4 Cisco 837 Router Network Connections

1	Corporate network connecting through a Cisco 3640 voice gateway	4	Dial backup or remote management that keeps the traffic working in case the primary line's traffic shuts down
2	Wholesale ISP business	5	PSTN to serve as an analog modem for dial backup or remote management
3	ISP POP (data center) with videoconferencing MCUs and IP/TV video servers	6	Small business or remote user, connecting to the network through a Cisco 837 router

In the topology, Cisco 837 routers send data packets from the remote user to the service provider or corporate network through high-speed, point-to-multipoint ADSL technology.

Internet Access Scenarios

Each network access scenario is described with a network diagram, configuration steps for setting up the network, and an example configuration.

Before You Configure Your Internet Access Network

You need to gather the following information before configuring networks based on the Internet access scenarios:

•Order an ADSL or G.SHDSL line from your public telephone service provider. For ADSL lines, determine that the ADSL signaling type is DMT, also called ANCII T1.413, or just DMT Issue 2. For G.SHDSL verify that the G.SHDSL line conforms to ITU standard G.991.2 and supports Annex A, for North America, or Annex B, for Europe.

•Gather information to set up a PPP Internet connection, including the PPP client name authentication type, and PPP password.

•Determine the IP routing information, including IP address, and ATM permanent virtual circuits (PVCs). These PVC parameters are typically virtual path identifier (vpi), virtual circuit identifier (vci), and traffic shaping parameters if applicable.

•Gather DNS server IP address and default gateways.

Replacing a Bridge or Modem with a Cisco 827 Router

This scenario shows a remote user connected to the Internet. You may want to use a network similar to this one if you want to set up a minimal connection to the Internet and bridge it through the Cisco 827 routers.

This network replaces an Alcatel 1000 bridge or modem with a Cisco 827 or Cisco 827-4V router by using AAL5SNAP encapsulation and bridging (RFC 1483 bridge mode) on the ATM interface.

Figure 2-5 shows the network topology for this scenario.

Figure 2-5 Replacing a Bridge or Modem with a Cisco 827 Router

1

Small business or remote user, connecting to the network through a Cisco 827 or Cisco 827-4V router

2

The Internet

The Cisco 827 router is configured to act as a bridge on the WAN, so the data packets are bridged through the 6400 router onto the Internet. This network setup creates the simplicity of bridging data but also maintains router control. This network is very simple but limits more complex services such as stopping broadcast traffic. If you want more services available on your network, you may want to consider Scenario 2 or 3.

Configuring the Scenario

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Note If you have only a single ATM PVC for your bridging network, you do not have to configure the protocol bridge broadcast.

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This scenario includes configuration tasks and a configuration example. To add additional features to this network, see "Basic Router Configuration," and "Advanced Router Configuration."

After configuring your router, you need to configure the PVC endpoint. For a general configuration example, see "Cisco 3640 Gateway Configuration Example" at the end of this chapter.

Follow the steps below to replace a bridge or modem with the Cisco 827 router, beginning in global configuration mode. Each step includes the same values that are shown in the bridging configuration example at the end of this section.

	Command	Purpose
Step 1	no ip routing	Disables IP routing.
Step 2	bridge 1 protocol ieee	Specifies the bridge protocol to define the type of Spanning-Tree protocol.
Step 3	interface ethernet 0	Enters configuration mode for the Ethernet interface.
Step 4	bridge-group 1	Specifies the bridge-group number to which the Ethernet interface belongs.
Step 5	no shutdown	Enables the Ethernet interface.
Step 6	exit	Exits configuration mode for the Ethernet interface and the router.
Step 7	interface ATM 0	Enters configuration mode for the ATM interface.
Step 8	pvc 8/35	Creates an ATM permanent virtual circuit (PVC) for each end node with which the router communicates.
Step 9	encapsulation aal5snap	Specifies the encapsulation type for the PVC.
Step 10	bridge-group 1	Specifies the bridge-group number to which the ATM interface belongs.
Step 11	no shutdown	Enables the ATM interface.
Step 12	exit	Exits the configuration mode for the ATM interface.

Configuration Example

The following is a configuration example for this network scenario. You do not have to enter the commands marked "default." These commands appear automatically in the configuration file generated when you use the show running-config command.

no ip routing

!

interface Ethernet0

no ip address

no ip directed-broadcast (default)

bridge-group 1

!

interface ATM0

no ip address

no ip directed-broadcast (default)

pvc 8/35 

encapsulation aal5snap

!

bridge-group 1

!

ip classless (default)

!

bridge 1 protocol ieee

!

end

PPP over Ethernet with NAT

The Cisco 837 and SOHO 97 routers support a PPP-over-Ethernet (PPPoE) client, with Network Addressing Translation (NAT) and with multiple PCs on the LAN. Figure 2-6 shows a typical deployment scenario for PPPoE support.

Figure 2-6 PPPoE Deployment Scenario

1	Multiple PCs in LAN	3	Access concentrator, concentrating data and LAN into ATM service over E1/T1 links
2	Multiple PCs connected in a LAN	4	PPPoE session. A PPPoE session is initiated on the client side by the Cisco 837 and SOHO 97 routers

A PPPoE session is initiated on the client side by the Cisco 837 or SOHO 97 router. If the session has a timeout, or if the session is disconnected, the PPPoE client immediately attempts to reestablish the session.

This section covers the following topics:

•Configuring the Virtual Private Dial-Up Network Group Number

•Configuring the ATM Interface

•Configuring the Dialer Interface

•Configuration Example

Configuring the Virtual Private Dial-Up Network Group Number

Follow the steps below to configure a virtual private dial-up network (VPDN), starting in global configuration mode.

	Command	Purpose
Step 1	vpdn enable	Enables VPDN.
Step 2	vpdn group tag	Sets the VPDN group.
Step 3	request-dialin	Specifies the dialing direction.
Step 4	protocol pppoe	Specifies the protocol type for the VPDN.
Step 5	interface ATM0 mtu 1492 pvc 8/35	Enters configuration mode for the ATM interface. Sets the maximum transmission unit (MTU) size and PVC number.
Step 6	pppoe-client dial-pool-number 1	Defines the PPPoE client in dial pool number 1.
Step 7	interface Dialer 1 ip address negotiated encapsulation ppp dialer-pool 1	Enters configuration mode for the Dialer 1 interface to obtain the IP address via IPCP. Specifies the encapsulation type for the PVC using dialer pool number 1.

Configuring the ATM Interface

Follow the steps below to configure the ATM interface, beginning in global configuration mode.

	Command	Purpose
Step 1	interface atm 0	Enters configuration mode for the ATM interface.
Step 2	dsl linerate {number | auto}	Specifies the DSL line rate. The range of valid numbers is from 72 to 2312. Note that this command is applicable only to Cisco 828 and SOHO 78 routers.
Step 3	ip address 200.200.100.1 255.255.255.0	Sets the IP address and subnet mask for the ATM interface.
Step 4	pvc vpi/vci	Creates an ATM PVC for each end node with which the router communicates.
Step 5	ppoe-client dial-pool-number 1	Binds the dialer to the interface.
Step 6	no shutdown	Enables the ATM 0 interface.

Configuring the Dialer Interface

Follow the steps below to configure the dialer interface, starting in global configuration mode.

	Command	Purpose
Step 1	ip route default-gateway-ip-address mask dialer 0	Sets the IP route for the default gateway for the Dialer 0 interface.
Step 2	interface dialer 0	Enters the Dialer 0 interface configuration.
Step 3	ip address negotiated	Specifies that the IP address is to be negotiated over PPP.
Step 4	ip mtu 1492	Sets the size of the IP maximum transmission unit (MTU).
Step 5	encapsulation ppp	Sets the encapsulation type to PPP.
Step 6	dialer pool 1	Specifies the dialer pool to be used.
Step 7	dialer-group 1	Assigns this interface to a dialer list.
Step 8	ppp authentication chap	Sets the PPP authentication method to Challenge Handshake Authentication Protocol (CHAP).
Step 9	exit	Exits the Dialer 0 interface configuration.
Step 10	dialer-list 1 protocol ip permit	Creates a dialer list for interested packets to be forwarded through the specified interface dialer group.

If you enter the clear vpdn tunnel pppoe command with a PPPoE client session already established, the PPPoE client session terminates, and the PPPoE client immediately tries to reestablish the session.

Configuration Example

The following example shows a configuration of a PPPoE client.

vpdn enable

vpdn-group 1

request-dialin

protocol pppoe

!

interface atm0

no ip address

no atm ilmi-keepalive

pvc 1/100

pppoe-client dial-pool-number 1

!

interface dialer 1

ip address negotiated

ppp authentication chap

dialer pool 1

dialer-group 1

!

dialer-list 1 protocol ip permit

PPP over Ethernet with NAT Using a Dial-on-Demand PPP-over- Ethernet Connection

The Cisco 831, Cisco 836, Cisco 837, Cisco SOHO 91, Cisco SOHO 96, and Cisco SOHO 97 routers support a PPP-over-Ethernet (PPPoE) client, using a dial-on-demand PPP-over-Ethernet connection. For deployment scenario, see Figure 2-6.

Configuring the Virtual Private Dial-Up Network Group Number

Complete the following tasks to configure a VPDN, starting in global configuration mode.

	Command	Purpose
Step 1	vpdn enable	Enables VPDN.
Step 2	vpdn group tag	Sets the VPDN group.
Step 3	request-dialin	Specifies the dialing direction.
Step 4	protocol pppoe	Specifies the protocol type for the VPDN.

Configuring the ATM Interface

Follow the steps below to configure the ATM interface, beginning in global configuration mode.

	Command	Purpose
Step 1	interface atm 0	Enters configuration mode for the ATM interface.
Step 2	ip address 200.200.100.1 255.255.255.0	Sets the IP address and subnet mask for the ATM interface.
Step 3	pvc vpi/vci	Creates an ATM PVC for each end node with which the router communicates.
Step 4	ppoe-client dial-pool-number 1 dial-on-demand	Binds the dialer to the interface.
Step 5	no shutdown	Enables the ATM 0 interface.

Configuring the Dialer Interface

Follow the steps below to configure the dialer interface, starting in global configuration mode.

	Command	Purpose
Step 1	ip route default-gateway-ip-address mask dialer 0	Sets the IP route for the default gateway for the Dialer 0 interface.
Step 2	interface dialer 0	Enters Dialer 0 interface configuration.
Step 3	ip address negotiated	Specifies that the IP address is to be negotiated over PPP.
Step 4	ip mtu 1492	Sets the size of the IP maximum transmission unit (MTU).
Step 5	ip nat outside	Establishes the Dialer 0 interface as the outside interface.
Step 6	encapsulation ppp	Sets the encapsulation type to PPP.
Step 7	dialer pool 1	Specifies the dialer pool to be used.
Step 8	dialer-group 1	Assigns this interface to a dialer list.
Step 9	ppp authentication chap	Sets the PPP authentication method to Challenge Handshake Authentication Protocol (CHAP).
Step 10	exit	Exits the Dialer 0 interface configuration.
Step 11	dialer-list 1 protocol ip permit	Creates a dialer list for packets of interest to be forwarded through the interface dialer group.

If you enter the clear vpdn tunnel pppoe command with a PPPoE client session already established, the PPPoE client session terminates, and the PPPoE client immediately tries to reestablish the session.

Configuration Example

The following example shows a configuration of a PPPoE client.

interface Ethernet0

no ip address

ip tcp adjust-mss 1400

no keepalive

hold-queue 100 out

!

vpdn enable

vpdn-group 1

request-dialin

protocol pppoe

!

interface atm0

no ip address

no atm ilmi-keepalive

pvc 1/100

pppoe-client dial-pool-number 1 dial-on-demand

!

interface dialer 1

ip address negotiated

ppp authentication chap

dialer pool 1

dialer-group 1

!

dialer-list 1 protocol ip permit

PPP over ATM with NAT

This network shows a user connected to the Internet through PPP over ATM and one static IP address. You may want to use this scenario in your network if you want to access the network with ATM support at the endpoints. PPP over ATM provides a network solution with simplified address handling and gives straight user verification as you would get in a dial network.

Figure 2-7 shows the network topology for this scenario.

Figure 2-7 PPP over ATM with NAT

1	Small business or remote user	3	PPP over ATM PVC 8/35
2	Connection to Ethernet 0 address 192.168.1.1/24 through a dialer interface	4	The Internet

In this scenario, the small business or remote user on the Ethernet LAN can connect to the Internet through ADSL. The Ethernet interface carries the data packet through the LAN and offloads it to the PPP connection on the ATM interface. The dialer interface is used to connect to the Internet or the corporate office. The number of ATM PVCs is set by default.

NAT (represented as the dashed line at the edge of the 827 routers) signifies two addressing domains and the inside source address. The source list defines how the packet travels through the network.

The following configuration topics are covered in this section:

•Configuring the Ethernet Interface

•Configuring the Dialer Interface

•Configuring the ATM Interface

•Configuring NAT

•Configuration Example

To add additional features to this network, see"Basic Router Configuration" and "Advanced Router Configuration."

After configuring your router, you need to configure the PVC endpoint. For a general configuration example, see"Cisco 3640 Gateway Configuration Example" at the end of this chapter.

Configuring the Ethernet interface

Follow the steps below to configure the Ethernet interface, beginning in global configuration mode.

	Command	Purpose
Step 1	interface ethernet 0	Enters configuration mode for the Ethernet interface.
Step 2	ip address 192.168.1.1 255.255.255.0	Sets the IP address and subnet mask for the Ethernet interface.
Step 3	no shutdown	Enables the interface and configuration changes just made to the Ethernet interface.
Step 4	exit	Exits configuration mode for the Ethernet interface.

Configuring the Dialer Interface

Follow the steps below to configure the dialer interface, beginning in global configuration mode.

	Command	Purpose
Step 1	interface dialer 0	Enters configuration mode for the dialer interface.
Step 2	ip address negotiated	Configures a negotiated IP address.
Step 3	ip nat outside	Sets the interface to be connected to the outside network.
Step 4	encapsulation ppp	Specifies the encapsulation type for the PVC to be PPP.
Step 5	dialer pool 1	Specifies which dialer pool number you are using.
Step 6	exit	Exits configuration mode for the dialer interface.

Configuring the ATM Interface

Follow the steps below to configure the ATM interface, beginning in global configuration mode.

	Command	Purpose
Step 1	interface ATM 0	Enters configuration mode for the ATM interface.
Step 2	pvc 8/35	Creates an ATM PVC for each end node with which the router communicates.
Step 3	encapsulation aal5mux ppp dialer	Specifies the encapsulation type for the PVC to be aal5mux (PPP) and point back to the dialer interface.
Step 4	dialer pool-member 1	Specifies a dialer pool-member.
Step 5	no shutdown	Enables interface and configuration changes just made to the ATM interface.
Step 6	exit	Exits configuration mode for the ATM interface.

Configuring NAT

Follow the steps below to configure NAT, beginning in global configuration mode.

	Command	Purpose
Step 1	ip nat inside source list 1 interface dialer 0 overload	Enables dynamic translation of addresses permitted by the access list to one of addresses specified in the dialer interface.
Step 2	ip route 0.0.0.0.0.0.0.0 dialer	Sets the ip route to point to the dialer interface as a default gateway.
Step 3	access-list 1 permit 192.168.1 0 0.0.0.255	Defines a standard access list permitting addresses that need translation.
Step 4	interface ethernet 0	Enters configuration mode for the Ethernet interface.
Step 5	ip nat inside	Establishes the Ethernet interface as the inside interface.
Step 6	no shutdown	Enables interface and configuration changes just made to the Ethernet interface.
Step 7	exit	Exits configuration mode for the Ethernet interface.

Configuration Example

In the following configuration example, you do not have to enter the commands marked "default." These commands appear automatically in the configuration file generated when you use the show running-config command.

interface Ethernet0

ip address 192.168.1.1 255.255.255.0

no ip directed-broadcast (default)

ip nat inside

!

interface ATM0

no ip address

no ip directed-broadcast (default)

ip nat outside

no atm ilmi-keepalive (default)

pvc 8/35 

encapsulation aal5mux ppp dialer

dialer pool-member 1

!

bundle-enable

!

interface Dialer0

ip address negotiated

no ip directed-broadcast (default)

ip nat outside

encapsulation ppp 

dialer pool 1

!         

ip nat inside source list 1 interface Dialer0 overload

ip classless (default)

ip route 0.0.0.0 0.0.0.0 Dialer 0 (default gateway)

!

access-list 1 permit 192.168.1.0 0.0.0.255

!

end

Configuring Dial Backup

By allowing you to configure a backup modem line connection, dial backup provides protection against WAN downtime. Dial backup is inactive until it is configured. On Cisco 831, Cisco 837, Cisco SOHO 91, and Cisco SOHO 97 routers, both the console port and the auxiliary port in the Cisco IOS software configuration are on the same physical RJ-45 port. Therefore, both ports cannot be activated simultaneously, and the command-line interface (CLI) must be used to enable or disable either one.

Like the Cisco 831 and Cisco 837 routers and the Cisco SOHO 91 and Cisco SOHO 97 routers, the Cisco 836 router supports dial-in (for remote management) and dial-out (for dial backup) capabilities across the ISDN interface. The Cisco SOHO 96 router supports only the dial-in feature. Unlike the Cisco 831 and Cisco 837 routers and the Cisco SOHO 91 and Cisco SOHO 97 routers, the dial backup and remote management functions are configured on the Cisco 836 and Cisco SOHO 96 routers through the router's ISDN S/T port.

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Note The remote management described in the "Configuring Dial Backup and Remote Management for the Cisco 837 and Cisco SOHO 97 Routers" section refers to backup remote management, the function that allows external control of the router via the ISDN when the ATM link goes down.

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Dial Backup Feature Limitations and Configuration

This section discusses the limitations and configuration of the dial backup feature on the Cisco 831, Cisco 836, and Cisco 837 routers and the Cisco SOHO 91, Cisco SOHO 96, and Cisco SOHO 97 routers.

Cisco 836 and Cisco 837 Routers and Cisco SOHO 96 and Cisco SOHO 97 Routers

The following can be used to bring up the dial backup feature in the Cisco IOS software for the Cisco 836 and Cisco 837 routers and the Cisco SOHO 96 and Cisco SOHO 97 routers:

•Backup Interfaces

•Floating Static Routes

•Dialer Watch

Backup Interfaces

When the device receives an indication that the primary line is down, the backup interface is brought up. You can configure the backup interface to go down (after a specified time) when the primary connection is restored.

The dial-on-demand routing (DDR) backup call is triggered by traffic of interest. Even if the backup interface comes out of standby mode, the router will not trigger the backup call unless it receives traffic of interest for that backup interface.

Floating Static Routes

Floating static routes depend on traffic of interest to trigger the DDR backup call. The router does not actually trigger the backup call unless it receives traffic of interest for that backup interface, even if the router installs the floating static route in the route table.

Floating static routes are independent of line protocol status. This is an important consideration on Frame Relay circuits wherein line protocol may not go down if the data-link connection identifier (DLCI) is inactive. Floating static routes are also encapsulation independent.

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Note When static routes are configured, the primary interface protocol must go down in order to activate the floating static route.

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Dialer Watch

Only the Extended Interior Gateway Routing Protocol (EIGRP) link-state dynamic routing protocols are supported.

There is a bottleneck in supporting bridging over console backup interfaces because bridging is not supported over slower interfaces such as console ports or auxiliary ports.

In the Cisco 836 and Cisco 837 routers, the dial backup feature is supported for the encapsulations identified in Table 2-1.

Table 2-1 Encapsulation Types Supported by Dial Backup Feature on the Cisco 836 and Cisco 837 Routers 

Encapsulation Type (WAN)	Dial Backup Possible	Type of Dial Backup Method	Limitations
PPP over ATM PPP over Ethernet	Yes	•Backup interface method •Floating static routes •Dialer watch	Floating static route and dialer watch need a routing protocol to run in the router. The dialer watch method brings up the backup interface as soon as the primary link goes down. The backup interface is brought down as soon as the dialer timeout is reached and the primary interface is up. Router checks the primary interface only when the dialer timeout expires. The backup interface remains up until the dialer timeout is reached, even though the primary interface is up. For the dialer watch method, a routing protocol does not need to be running in the router, if the IP address of the peer is known.
RFC 1483 (AAL5, SNAP, and MUX)	Yes	•Backup interface method •Floating static routes •Dialer watch	If bridging is done through the WAN interface, it is not supported across the auxiliary port.

Cisco 831 and Cisco SOHO 91 Routers

Support for the dial backup feature on the Cisco 831 router is limited because the Ethernet WAN interface is always up, even when ISP connectivity is down across the modem connected to the Cisco 831 router. Support for dial backup is possible only for the PPPoE environment. The only way to bring up the backup interface is to simultaneously use the dialer watch feature. You also need to add the IP addresses of the peer in the dialer watch command and in the static route command to enable the dial backup when primary line goes down.

For the Cisco SOHO 91 router, only dial-in capability is supported.

Table 2-2 shows the encapsulation types supported by the Cisco 831 router dial backup.

Table 2-2 Encapsulation Types Supported by Dial Backup for the Cisco 831 Router

Encapsulation Type	Dial Backup Possible	Type of Dial Backup Method	Limitations
PPPoE	Yes	Dialer watch	Bridging is not supported across a slow interface, for example, an auxiliary port. The peer IP address of the ISP provider is needed to configure the dialer watch command and the IP static route.
Normal IP in cable modem scenario	No	Dialer watch	The IP addresses of the peers are needed for dialer watch to work properly. If a lease time obtained by DHCP is not set short enough (one or two minutes), dial backup will not be supported.

Configuring Dial Backup and Remote Management for the Cisco 837 and Cisco SOHO 97 Routers

Figure 2-8 shows how dial backup and remote management work in a network system when the primary line goes down.

Figure 2-8 Cisco 837 Router Dial Backup and Remote Management

1	Main WAN link; primary connection to Internet service provider
2	Dial backup; serves as a failover link when primary line goes down
3	Remote management; serves as dial-in access to allow changes or updates to Cisco IOS configurations

Configuring Dial Backup and Remote Management for the Cisco 836 and Cisco SOHO 96 Routers

Figure 2-9 and Figure 2-10 show how dial backup and remote management work in a network system when the primary line goes down. Two scenarios are typical applications of the Cisco 836 and the Cisco SOHO 96 routers. In Figure 4-9, the dial backup link goes through CPE splitter, DSLAM, and CO splitter before connecting to the ISDN switch. In Figure 4-10, the dial backup link goes directly from the Cisco 836 router to the ISDN switch.

Figure 2-9 Cisco 836 Router Dial Backup and Remote Management—Dial Backup Through CPE Splitter, DSLAM, and CO Splitter

1	Primary ADSL interface
2	Dial backup and remote management via ISDN interface; serves as a failover link when primary line goes down
3	Administrator remote management via ISDN interface when the primary ADSL link is down; serves as dial-in access to allow changes or updates to Cisco IOS configuration

Figure 2-10 Cisco 836 Router Dial Backup and Remote Management—Dial Backup Directly from Router to ISDN Switch

1	Primary ADSL interface
2	Dial backup and remote management via ISDN interface; serves as a failover link when primary line goes down
3	Administrator remote management via ISDN interface when the primary ADSL link is down; serves as dial-in access to allow changes or updates to Cisco IOS configuration

PPP over ATM with Centrally Managed Addressing and with Dial Backup

When customer premises equipment such as a Cisco 837 router is connected to an ISP, an IP address is dynamically assigned to the router, or the IP address may be assigned by its peer through the centrally managed function. The dial backup feature can be added to provide a failover route in case the primary line fails.

Configuring Dial Backup and Remote Management for the Cisco 837 Router

Follow the steps below to configure dial backup and remote management for the Cisco 837 router.

	Command	Purpose
Step 1	ip name-server 206.13.28.12	Enters your ISP DNS IP address.
Step 2	ip dhcp pool 1	Configures CPE as a local DHCP server.
Step 3	vpdn enable	Enables VPDN.
Step 4	vpdn-group 1	Specifies VPDN group for protocol PPPoE.
Step 5	chat-script Dialout ABORT ERROR ABORT BUSY "" "AT" OK "ATDT 5555102 T" TIMEOUT 45 CONNECT \c	Configures a chat script for a modem.
Step 6	interface Async1	Enters configuration mode for the async interface.
Step 7	interface Dialer3	Enters configuration mode for the dialer interface.
Step 8	dialer watch-group 1	Specifies the group number for watch-list.
Step 9	ip nat inside source list 101 interface Dialer3 overload	Establishes the Ethernet interface as the inside interface.
Step 10	ip route 0.0.0.0 0.0.0.0 ! (dial backup peer address @ISP)	Sets the IP route to point to the dialer interface as a default gateway.
Step 11	access-list 101 permit ip 192.168.0.0 0.0.255.255 any	Defines an extended access list permitting addresses that need translation.
Step 12	dialer watch-list 1 ip ! (ATM peer address @ISP) 255.255.255.255	Evaluates the status of the primary link, based on the existence of routes to the peer.
Step 13	line con 0	Enters configuration mode for the console interface.
Step 14	modem enable	Changes the console port to auxiliary port function.
Step 15	line aux 0	Enters configuration mode for the auxiliary interface.
Step 16	flow control hardware	Enables hardware signal flow control.

Configuration Example

The following configuration example for a Cisco 837 router specifies an IP address for the ATM interface via PPP/IPCP address negotiation and dial backup over the console port.

!

version 12.2

no service pad

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname Router

!

memory-size iomem 20

enable password cisco

!

ip subnet-zero

ip name-server 206.13.28.12

ip name-server 206.13.31.12

ip name-server 63.203.35.55

ip dhcp excluded-address 192.168.1.1

!

ip dhcp pool 1

import all

network 192.168.1.0 255.255.255.0

default-router 192.168.1.1

! 

ip audit notify log

ip audit po max-events 100

vpdn enable

!

vpdn-group 1

request-dialin

protocol pppoe

!

! Need to use your own correct ISP phone number

modemcap entry MY-USER_MODEM:MSC=&F1S0=1

chat-script Dialout ABORT ERROR ABORT BUSY "" "AT" OK "ATDT 5555102\T"

TIMEOUT 45 CONNECT \c

!

!

!

!

interface Ethernet0

ip address 192.168.1.1 255.255.255.0

ip nat inside

ip tcp adjust-mss 1452

hold-queue 100 out

!

interface ATM0

mtu 1492

no ip address

no atm ilmi-keepalive

pvc 0/35

pppoe-client dial-pool-number 1

!

dsl operating-mode auto

!

!Dial backup and remote management physical interface

interface Async1

no ip address

encapsulation ppp

dialer in-band

dialer pool-member 3

async default routing

async dynamic routing

async mode dedicated

ppp authentication pap callin

!

! Primary wan link

interface Dialer1

ip address negotiated

ip nat outside

encapsulation ppp

dialer pool 1

ppp authentication pap callin

ppp pap sent-username account password 7 pass

ppp ipcp dns request

ppp ipcp wins request

ppp ipcp mask request

!

! Dialer backup logical interface

interface Dialer3

ip address negotiated

ip nat outside

encapsulation ppp

no ip route-cache

no ip mroute-cache

dialer pool 3

dialer idle-timeout 60

dialer string 5555102 modem-script Dialout

dialer watch-group 1

!

! Remote management PC ip address

peer default ip address 192.168.2.2

no cdp enable

!

! Need to use your own ISP account and password

ppp pap sent-username account password 7 pass

ppp ipcp dns request

ppp ipcp wins request

ppp ipcp mask request

!

! IP NAT over Dialer interface using route-map

ip nat inside source route-map main interface Dialer1 overload

ip nat inside source route-map secondary interface Dialer3 overload

ip classless

!

! When primary link is up again, distance 50 will override 80 if dial backup hasn't 
timeout