Example 17-24 Verify Symptom by Issuing a | CCNA Practical Studies (Cisco Certification & Training)

Scenario 3

Symptom: In the lab, R6 represents a remote office that connects to the main network over ISDN. You configured legacy DDR to connect these remote users on network 192.168.60.0 (R6's Token Ring network) to the main corporate network when IP traffic was present to send. You receive a call reporting that remote users on network 192.168.60.0 are unable to access IP resources on network 192.168.3.0 (R3's Ethernet 0 network).

Objective: You will have resolved this issue when you can successfully ping 192.168.3.3 from R6.

First, isolate the problem and verify that the reported symptom is accurate by issuing a ping from R6 to 192.168.3.3, as shown in Example 17-24.

Example 17-24 Verify Symptom by Issuing a ping to 192.168.3.3

 R6#  ping 192.168.3.3  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.3.3, timeout is 2 seconds: ..... Success rate is 0 percent (0/5) R6#

You definitely have an issue. Next, you need to determine the layer at which you are having problems. To begin, examine the interfaces on R6 to ensure that the BRI 0 interface is up, as shown in Example 17-25.

Example 17-25 Using show ip interface brief Command to Determine Current Interface Status

 R6#  show ip interface brief  Interface              IP-Address      OK? Method Status                Protocol  BRI0                   192.168.200.2   YES NVRAM  up                    up  BRI0:1                 unassigned      YES unset  down                  down BRI0:2                 unassigned      YES unset  down                  down Loopback0              192.169.6.6     YES NVRAM  up                    up Serial0                unassigned      YES unset  administratively down down Serial1                unassigned      YES unset  administratively down down TokenRing0             192.168.60.6    YES NVRAM  up                    up R6#

You can see that interface BRI 0 is up, has not been administratively shut down, and has the correct IP address of 192.168.200.2 assigned. Next, do a show isdn status to verify that ISDN Layers 1, 2, and 3 appear as you would expect, as demonstrated in Example 17-26.

Example 17-26 Checking ISDN Layers 1, 2, and 3 with show isdn status Command

 R6#  show isdn status   The current ISDN Switchtype = basic-5ess  ISDN BRI0 interface     Layer 1 Status:  ACTIVE  Layer 2 Status:  TEI = 101, State = MULTIPLE_FRAME_ESTABLISHED  Layer 3 Status:         0 Active Layer 3 Call(s)     Activated dsl 0 CCBs = 0     Total Allocated ISDN CCBs = 0 R6#

As the highlighted output indicates, the ISDN switch type (basic-5ess) is correct and Layer 1 shows ACTIVE. Also, Layer 2 appears okay, as indicated by State = MULTIPLE_FRAME_ESTABLISHED. So far, it appears that the issue might be at Layer 3. Review those items configured on R6 applicable to legacy DDR configuration at Layer 3:

The BRI 0 interface IP address and subnet mask
A default route pointing to R5's BRI0 interface
A dialer-list statement defining IP as interesting traffic
Applying a dialer group defining interesting traffic for the interface

Examine each of these four items to determine whether you can find something that might be causing the problem. Verify that the mask on R6's BRI0 has not been changed using the command s how interface bri0, as shown in Example 17-27.

Example 17-27 Check IP Address and Mask of Interface BRI 0 Using show interface bri0 Command

 R6#  show interface bri0  BRI0 is up, line protocol is up (spoofing)   Hardware is BRI  Internet address is 192.168.200.2/30  MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255   Encapsulation PPP, loopback not set   Last input 00:00:23, output 00:00:23, output hang never   Last clearing of "show interface" counters never   Input queue: 0/75/0 (size/max/drops); Total output drops: 0   Queueing strategy: weighted fair   Output queue: 0/1000/64/0 (size/max total/threshold/drops)      Conversations  0/1/256 (active/max active/max total)      Reserved Conversations 0/0 (allocated/max allocated)   5 minute input rate 0 bits/sec, 0 packets/sec   5 minute output rate 0 bits/sec, 0 packets/sec      3058 packets input, 12254 bytes, 0 no buffer      Received 6 broadcasts, 0 runts, 0 giants, 0 throttles      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort      3058 packets output, 12249 bytes, 0 underruns      0 output errors, 0 collisions, 7 interface resets      0 output buffer failures, 0 output buffers swapped out      3 carrier transitions R6#

The IP address and mask are correct. Next, ensure that R6 has a default route pointing to R5's BRI 0 interface's IP address of 192.168.200.1 using the show ip route command, as demonstrated in Example 17-28.

Example 17-28 Verify That R6 Has a Default Route Pointing to 192.168.200.1

 R6#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is 192.168.200.1 to network 0.0.0.0 C    192.168.60.0/24 is directly connected, TokenRing0 C    192.169.6.0/24 is directly connected, Loopback0      192.168.200.0/30 is subnetted, 1 subnets C       192.168.200.0 is directly connected, BRI0  S*   0.0.0.0/0 [1/0] via 192.168.200.1  R6#

You can see that the default route pointing to R5's BRI 0 shows up as expected. Third, debug the dialer packets and then issue a ping to 192.168.3.3. Do this using the command debug dialer packets and then examine the results of the output as displayed in Example 17-29.

Example 17-29 Use debug dialer packets to Determine Status of Outgoing IP Packets over the ISDN Link

 R6#  debug dialer packets  Dial on demand packets debugging is on R6#ping 192.168.3.3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.3.3, timeout is 2 seconds: ..... Success rate is 0 percent (0/5) R6#  BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, uninteresting (dialer-list 1   not defined)  BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, uninteresting (dialer-list 1   not defined) BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, uninteresting (dialer-list 1   not defined) BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, uninteresting (dialer-list 1   not defined) BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, uninteresting (dialer-list 1   not defined) R6#

Notice from the highlighted portion of Example 17-29 that each ping packet fails. You are given the additional debug output indicating that the packets are considered "uninteresting" because dialer-list 1 is not defined. This points to the dialer list configuration. Examine the running config of R6 as shown in Example 17-30.

Example 17-30 Examine the Running Configuration on R6 to Verify Configuration of dialer-list 1

 R6#  show running-config  Building configuration... Current configuration: ! version 11.2 no service password-encryption no service udp-small-servers no service tcp-small-servers ! hostname R6 ! enable password falcons ! ip subnet-zero no ip domain-lookup ip host R6 192.169.6.6 ip host R1 192.169.1.1 ip host R2 192.169.2.2 ip host R3 192.169.3.3 ip host R4 192.169.4.4 ip host R5 192.169.5.5 isdn switch-type basic-5ess ! interface Loopback0  ip address 192.169.6.6 255.255.255.0 ! interface Serial0  no ip address  shutdown  no fair-queue ! interface Serial1  no ip address  shutdown ! interface TokenRing0  description This interface does not connect with another IP device  ip address 192.168.60.6 255.255.255.0  ring-speed 16 ! interface BRI0  ip address 192.168.200.2 255.255.255.252  encapsulation ppp  dialer idle-timeout 300  dialer string 8358662  dialer-group 1  !no ip classless ip route 0.0.0.0 0.0.0.0 192.168.200.1 ! banner motd ^C This is Router 6 ^C ! line con 0  exec-timeout 0 0  password falcons  logging synchronous line aux 0 line vty 0 4  password falcons  login ! end R6#

The highlighted portion of R6's running config indicates that the BRI0 interface has the appropriate dialer group assigned. However, when you examine the configuration more closely, you notice that the dialer-list statement defining all IP traffic as interesting has been removed from the configuration. Normally, you would expect to see the dialer list after the static routes and before the banner configuration. Correct this on R6, as demonstrated in Example 17-31.

Example 17-31 Correcting the dialer-list 1 Configuration

 R6#  conf t  Enter configuration commands, one per line.  End with CNTL/Z. R6(config)#  dialer-list 1 protocol ip permit  R6(config)#  ^Z  R6#

Now that the appropriate dialer list has been configured, ping 192.168.3.3 and observe the debug output as shown in Example 17-32.

Example 17-32 debug Output Now Shows That IP Traffic Is Considered "Interesting," in Turn Bringing Up the ISDN Link

 R6#  ping 192.168.3.3  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.3.3, timeout is 2 seconds:  ..!!!  Success rate is 60 percent (3/5), round-trip min/avg/max = 40/44/48 ms R6#  BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, interesting (ip PERMIT)  %LINK-3-UPDOWN: Interface BRI0:1, changed state to up BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, interesting (ip PERMIT) BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, interesting (ip PERMIT) BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, interesting (ip PERMIT) %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state to up BRI0: cdp, 284 bytes, uninteresting (no list matched) BRI0: sending broadcast to default destination BRI0: ip (s=192.168.200.2, d=192.168.3.3), 100 bytes, interesting (ip PERMIT) R6#  %ISDN-6-CONNECT: Interface BRI0:1 is now connected to 8358662  R6#

Notice the three highlighted sections. The first shows that the initial ping packets fail and that then you get three successful ping s. At this point, you know that the link is up. Next, you can see that the traffic now is considered interesting, causing the link to come up. Lastly, you see that you are connected to 8358662. Turn off debugging using undebug all, and then save the changes, as shown in Example 17-33.

Example 17-33 Turning Off All Debugging and Saving the Configuration

 R6#  undebug all  All possible debugging has been turned off R6#  copy run start  Building configuration... [OK] R6#

You now have successfully resolved this ISDN issue.

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