Cisco Router 826 Routers Software Configuration Guide
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2-17 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup 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. NoteWhen static routes are configured, the primary interface protocol must go down in order to activate the floating static route. 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 Ta b l e 2 - 1.
2-18 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup 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. Ta b l e 2 - 2 shows the encapsulation types supported by the Cisco 831 router dial backup. Table 2-1 Encapsulation Types Supported by Dial Backup Feature on the Cisco 836 and Cisco 837 Routers Encapsulation Ty p e ( W A N )Dial Backup PossibleType of Dial Backup Method Limitations PPP over ATM PPP over EthernetYe s Backup interface method Floating static routes Dialer watchFloating 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)Ye s Backup interface method Floating static routes Dialer watchIf bridging is done through the WAN interface, it is not supported across the auxiliary port.
2-19 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup 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 Table 2-2 Encapsulation Types Supported by Dial Backup for the Cisco 831 Router Encapsulation TypeDial Backup PossibleType 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 scenarioNo 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. 1Main WAN link; primary connection to Internet service provider 2Dial backup; serves as a failover link when primary line goes down 3Remote management; serves as dial-in access to allow changes or updates to Cisco IOS configurations 82269 1 3 2 23 AT M 837 Modem Modem Modem PC3620 PSTN
2-20 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup 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 1Primary ADSL interface 2Dial backup and remote management via ISDN interface; serves as a failover link when primary line goes down 3Administrator 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 82892 Cisco 836CPE splitterAT M networkATM Aggregator Internet Web server Administrator ISDN switch ISDNISDN Peer Router CO splitter DSLAM 2 3 1
2-21 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup Figure 2-10 Cisco 836 Router Dial Backup and Remote Management—Dial Backup Directly from Router to ISDN Switch 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.1Primary ADSL interface 2Dial backup and remote management via ISDN interface; serves as a failover link when primary line goes down 3Administrator 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 88208 PC836CPE splitterAT M networkAggregator Internet Web server Administrator ISDN switch DSLAM 2 3 1 Command Purpose Step 1ip name-server 206.13.28.12Enters your ISP DNS IP address. Step 2ip dhcp pool 1Configures CPE as a local DHCP server. Step 3vpdn enableEnables VPDN. Step 4vpdn-group 1Specifies VPDN group for protocol PPPoE. Step 5chat-script Dialout ABORT ERROR ABORT BUSY ““ “AT” OK “ATDT 5555102 T” TIMEOUT 45 CONNECT \c Configures a chat script for a modem. Step 6interface Async1Enters configuration mode for the async interface. Step 7interface Dialer3Enters configuration mode for the dialer interface.
2-22 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup 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 Step 8dialer watch-group 1Specifies the group number for watch-list. Step 9ip nat inside source list 101 interface Dialer3 overloadEstablishes the Ethernet interface as the inside interface. Step 10ip 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 11access-list 101 permit ip 192.168.0.0 0.0.255.255 anyDefines an extended access list permitting addresses that need translation. Step 12dialer watch-list 1 ip ! (ATM peer address @ISP) 255.255.255.255Evaluates the status of the primary link, based on the existence of routes to the peer. Step 13line con 0Enters configuration mode for the console interface. Step 14modem enableChanges the console port to auxiliary port function. Step 15line aux 0Enters configuration mode for the auxiliary interface. Step 16flow control hardwareEnables hardware signal flow control. Command Purpose
2-23 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup 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
2-24 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup 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 ! Multiple routes because peer ip addresses are alternated among them when CPE gets connected ip route 0.0.0.0 0.0.0.0 64.161.31.254 50 ip route 0.0.0.0 0.0.0.0 66.125.91.254 50 ip route 0.0.0.0 0.0.0.0 64.174.91.254 50 ip route 0.0.0.0 0.0.0.0 63.203.35.136 80 ip route 0.0.0.0 0.0.0.0 63.203.35.137 80 ip route 0.0.0.0 0.0.0.0 63.203.35.138 80 ip route 0.0.0.0 0.0.0.0 63.203.35.139 80 ip route 0.0.0.0 0.0.0.0 63.203.35.140 80 ip route 0.0.0.0 0.0.0.0 63.203.35.141 80 ip route 0.0.0.0 0.0.0.0 Dialer1 150 no ip http server ip pim bidir-enable ! ! PC ip address behind CPE access-list 101 permit ip 192.168.0.0 0.0.255.255 any access-list 103 permit ip 192.168.0.0 0.0.255.255 any ! ! Watch multiple ip address because peers are alternated among them when CPE gets connected dialer watch-list 1 ip 64.161.31.254 255.255.255.255 dialer watch-list 1 ip 64.174.91.254 255.255.255.255 dialer watch-list 1 ip 64.125.91.254 255.255.255.255 ! ! Dial backup will kick in if primary link is not available 5 minutes after CPE starts up dialer watch-list 1 delay route-check initial 300 dialer-list 1 protocol ip permit ! ! To direct traffic to an interface only if the Dialer gets assigned with an ip address route-map main permit 10 match ip address 101 match interface Dialer1 ! route-map secondary permit 10 match ip address 103 match interface Dialer3 ! ! line con 0 exec-timedout 0 0 ! ! Change console to aux function modem enable stopbits 1 line aux 0 exec-timeout 0 0 ! ! To enable and communicate with the external modem properly script dialer Dialout modem InOut modem autoconfigure discovery transport input all stopbits 1
2-25 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup speed 115200 flowcontrol hardware line vty 0 4 exec-timeout 0 0 password cisco login ! scheduler max-task-time 5000 end Configuring Dial Backup and Remote Management for the Cisco 836 Router Follow the steps given in the “Configuring the Cisco 836 Router’s ISDN Settings” section on page 2-25 to configure dial backup and remote management on the Cisco 836 router’s ISDN S/T port. Configuring the Cisco 836 Router’s ISDN Settings The user must first configure the Cisco 836 router ISDN settings to configure the router interface as a backup interface. Follow the steps below to configure the Cisco 836 router ISDN interface as a backup interface, beginning in global configuration mode. NoteTraffic of interest must be present to activate the backup ISDN line by means of the backup interface and floating static routes methods. Traffic of interest is not needed for the dialer watch to activate the backup ISDN line. Command Purpose Step 1isdn switch-type basic-net3Specifies the ISDN switch type. Step 2interface BRI0Enters configuration mode for the ISDN Basic Rate Interface (BRI). Step 3encapsulation pppSets BRI0 interface encapsulation type to PPP. Step 4dialer pool-member 1Specifies the dialer pool membership. Step 5isdn switch-type basic-net3Specifies the ISDN switch type. Step 6exitExits to return to global configuration mode. Step 7interface Dialer0Enters configuration mode for the dialer interface. Step 8ip address negotiatedObtains the IP address from the peer. Step 9encapsulation pppSpecifies Dialer 0 encapsulation type as PPP. Step 10dialer pool 1Specifies the dialer pool to be used. Dialer pool 1 setting associates Dialer 0 interface with BRI0 because the BRI0 dialer pool-member value is “1.” Step 11dialer string 384040Specifies the telephone number to be dialed. Step 12dialer-group 1Assigns this interface to a dialer group.
2-26 Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide 78-14565-03 Chapter 2 Network Scenarios Configuring Dial Backup Configuring Dial Backup and Remote Management Settings As described in the “Dial Backup Feature Limitations and Configuration” section on page 2-16, backup interface, static routes, and dialer watch are the three methods used for implementing dial backup and remote management. This section provides detailed procedures for configuring these three methods. Configuring Backup Interface Follow the steps below to configure the Cisco 836 router ISDN interface as a backup interface, beginning in global configuration mode. Configuring Floating Static Route Static route and dynamic route are the two components of floating static routes. Complete the following steps to configure the static route on the Cisco 836 router ISDN port, beginning in global configuration mode. NoteWhen the static routes are configured, the primary interface protocol must go down in order to activate the floating static route. Step 13exitExits to return to global configuration mode. Step 14dialer-list 1 protocol ip permitCreates a dialer list for packets of interest to be forwarded through the specified interface dialer group. Dialer-list 1 corresponds to dialer-group 1. Command Purpose Command Purpose Step 1interface ATM0Enters ATM interface configuration mode. Step 2backup interface BRI0Assigns BRI0 as the secondary backup interface. Command Purpose Step 1ip route 0.0.0.0 0.0.0.0 22.0.0.2Assigns the primary route. Step 2ip route 0.0.0.0 0.0.0.0 192.168.2.2 150Assigns the lower routing administrative distance value for the backup interface route. 192.168.2.2 is the peer IP address of the backup interface.