Lab Configuring ISDN Dial Backup

Transcription

1 Lab Configuring ISDN Dial Backup Objective Configure ISDN dial backup for a fixed Frame Relay WAN link. Scenario The network engineer for the International Travel Agency (ITA) is responsible for full-time WAN connectivity between regional headquarters and San Jose company headquarters. Frame Relay permanent virtual circuits (PVC) have been made into a star topology, with SanJose1 as the hub router. To provide fault tolerance, each Frame Relay PVC is backed up with ISDN BRI. Step 1 Step 2 Build the network as shown in the diagram. If the Atlas 550 is used as a WAN emulator, be sure to use the ports as indicated in the diagram. Before beginning this lab, it is recommended that each router be reloaded after erasing its startup configuration. This will prevent problems that may be caused by residual configurations. Use the following to configure and test ISDN BRI on Capetown, using CHAP authentication: Capetown(config)#isdn switch-type basic-ni Capetown(config)#username SanJose1 password cisco Capetown(config)#dialer-list 1 protocol ip permit Capetown(config)#interface bri 0/0 Capetown(config-if)#ip address Capetown(config-if)#encapsulation ppp Capetown(config-if)#ppp authentication chap Capetown(config-if)#isdn spid CCNP 2: Remote Access v 3.1 Lab Copyright 2003, Cisco Systems, Inc.

2 Capetown(config-if)#isdn spid Capetown(config-if)#dialer map ip name SanJose1 broadcast Capetown(config-if)#dialer idle-timeout 60 Capetown(config-if)#dialer-group 1 Next, configure SanJose1 as shown in the following: Note: SanJose1 will only accept BRI calls, so do not configure a phone number with the dialer map statement. SanJose1(config)#isdn switch-type basic-ni SanJose1(config)#username Capetown password cisco SanJose1(config)#dialer-list 1 protocol ip permit SanJose1(config)#interface bri 0/0 SanJose1(config-if)#ip address SanJose1(config-if)#encapsulation ppp SanJose1(config-if)#ppp authentication chap SanJose1(config-if)#isdn spid SanJose1(config-if)#isdn spid SanJose1(config-if)#dialer map ip name Capetown broadcast SanJose1(config-if)#dialer idle-timeout 60 SanJose1(config-if)#dialer-group 1 Step 3 Ping across the ISDN link from Capetown to SanJose1 ( ). This ping should be successful. Troubleshoot as necessary. Configure and test Frame Relay connectivity on both routers. The following is an example of the Capetown configuration: Capetown(config)#interface s0/0 Capetown(config-if)#ip address Capetown(config-if)#encapsulation frame-relay Capetown(config-if)#frame-relay map ip broadcast Step 4 Use ping to verify that the Frame link is operational. Ping one serial interface from the other. Configure and test static routing between the Capetown spoke router and the SanJose1 hub router. Because Capetown supports a stub network, create a static route to all unknown networks pointing at SanJose1. SanJose1 will use a specific static route to return packets to the Capetown LAN, as shown in the following: SanJose1(config)#ip route Capetown(config)#ip route Step 5 Verify that the static routing configuration works by performing extended pings between LANs. Configure ISDN dialup backup routing. The Frame Relay link has adequate bandwidth for normal traffic. The ISDN BRI is deployed only for fault tolerance. The service provider will charge for each minute of ISDN call time if the defined data transfer levels are exceeded. Having a redundant path is worth the cost, but use of the line needs to be minimized to avoid associated charges. 2-5 CCNP 2: Remote Access v 3.1 Lab Copyright 2003, Cisco Systems, Inc.

3 Use the following configuration to place floating static routes between SanJose1 and Capetown, utilizing the ISDN link: Capetown(config)#ip route SanJose1(config)#ip route The following are views of the routing tables: SanJose1#show ip route Gateway of last resort is not set S /24 [1/0] via C /24 is directly connected, BRI0/0 C /24 is directly connected, FastEthernet0/0 Capetown#show ip route Gateway of last resort is to network C /24 is directly connected, FastEthernet0/0 C /24 is directly connected, BRI0/0 S* /0 [1/0] via Although two static routes have been configured on each router, only one of those routes is installed in each routing table. Why? The static routes using the Frame Relay link have a default administrative distance of one (1). This is preferred over all routes except directly connected routes, which have an administrative distance of zero (0). If the Frame Relay link fails, associated routes will eventually be removed from the routing table. ISDN routes with an administrative distance of 222 will then be placed in the routing table. Connectivity will be restored, although at a much slower rate. The ISDN link is to be active only in the event of a Frame Relay link failure. Enter the following configuration to make BRI 0/0 a backup interface to Serial0/0 on Capetown: Capetown(config)#interface s0/0 Capetown(config-if)#backup interface bri0/0 Capetown(config-if)#backup delay 6 8 Only Capetown is configured with the backup interface and backup delay commands. The first backup delay value six (6) represents the number of seconds between Serial 0/0 failure and the backup link (BRI 0/0) becoming active. The second value eight (8) is the number of seconds after Serial 0/0 is restored before bringing down the backup link. If the SanJose1 BRI were configured as a backup interface, Capetown could not establish a dialup connection with SanJose1. The SanJose1 BRI would either be in standby mode or trying to make a dialup call. In either case, Capetown would not be able to connect with it. The following is another look at the Capetown routing table: Capetown#show ip route Gateway of last resort is to network C /24 is directly connected, FastEthernet0/0 S* /0 [1/0] via CCNP 2: Remote Access v 3.1 Lab Copyright 2003, Cisco Systems, Inc.

4 Step 6 The directly connected route for the ISDN link has disappeared. Enter the following to check to see if the BRI is down by issuing the show interface command on Capetown: Capetown#show interface bri0/0 BRI0/0 is standby mode, line protocol is down Hardware is PQUICC BRI with U interface Internet address is /24 MTU 1500 bytes, BW 64 Kbit, DLY usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation PPP, loopback not set <output omitted> The output of this command shows that the line is down, but standing by, in the event the serial interface goes down. On Capetown, issue the show backup command as shown in the following: Capetown#show backup Primary Interface Secondary Interface Status Serial0/0 BRI0/0 normal operation Enter the following to test dial backup with an extended ping between Capetown and SanJose1: Note: While the ping progresses, disconnect the serial cable from both routers. Capetown#ping Protocol [ip]: Target IP address: Repeat count [5]: 555 Datagram size [100]: Timeout in seconds [2]: 1 Extended commands [n]: y Source address or interface: Type of service [0]: Set DF bit in IP header? [no]: Validate reply data? [no]: Data pattern [0xABCD]: Loose, Strict, Record, Timestamp, Verbose[none]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 555, 100-byte ICMP Echos to , timeout is 1 seconds:!!!!...!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Success rate is 98 percent (545/555), round-trip min/avg/max = 32/39/60 ms It took over five seconds for ISDN to become active after Frame Relay failed. While active, the backup interface is in backup mode. Issue the show backup command on Capetown, as shown in the following: Capetown#show backup Primary Interface Secondary Interface Status Serial0/0 BRI0/0 backup mode 4-5 CCNP 2: Remote Access v 3.1 Lab Copyright 2003, Cisco Systems, Inc.

5 1. How did Capetown get to SanJose1 if the only route was through the failed Frame Relay link? To verify the answer to Question 2, issue show ip route on Capetown. The following route should now be in the Capetown routing table: C /24 is directly connected, BRI0/0 When Serial 0/0 failed, its associated static route was removed from the routing table and replaced by the floating static route over the ISDN link. Enter the following to verify that the SanJose1 ISDN interface is up by issuing the show interface bri0/0 command: SanJose1#show interface bri0/0 BRI0/0 is up, line protocol is up (spoofing) Hardware is PQUICC BRI with U interface Internet address is /24 MTU 1500 bytes, BW 64 Kbit, DLY usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation PPP, loopback not set <output ommited> The dial backup for WAN connectivity has now been successfully implemented. 5-5 CCNP 2: Remote Access v 3.1 Lab Copyright 2003, Cisco Systems, Inc.