Chapter 9's Review Questions
| 1: | Why do interface resets occur? |
| A1: | Answer: Interface resets occur when the interface has been completely reset, which normally is from cabling or signaling issues. The system resets the interface automatically if it sees that the physical interface is up, but the line protocol is down. Carrier transitions occur when an interruption in signal occurs. If DCD goes down and then back up, for example, that is two transitions. If they continue to increase, check the cabling or other attached hardware. If output drops also increase, the problem may be congestion. |
| 2: | True or false: The ISDN signaling protocol is LAPB for the D channel. |
| A2: | Answer: False. LAPB is for X.25. LAPD is the signaling protocol for the ISDN D channel. The ISDN B channels are for data, voice, and video and use HDLC or PPP encapsulation. |
| 3: | The modem control leads on show interfaces s0 are quite helpful for troubleshooting. DCD keeps changing state. What else on the interface statistics would you expect to be increasing? Look at Example 9-13 if you need to see a display of the modem control leads. |
| A3: | Answer: The modem control leads are quite helpful for troubleshooting. If the DCD keeps changing state, the carrier transitions may in turn drop and reset the line due to the failure to output queued packets. |
| 4: | Your router has a native ISDN BRI port. Is this device a TE1 or TE2? |
| A4: | Answer: If your router has a native ISDN port, it is a TE1. A TE2 is a router or PC without an ISDN port that connects via a terminal adapter. Review Figure 9-7 and Figure 9-8. |
| 5: | What is the difference between Multilink PPP and dial backup? |
| A5: | Answer: Multilink PPP is used to aggregate traffic over multiple channels simultaneously. Dial backup is having a secondary link for when the primary fails. They are not the same. |
| 6: | Use the first HDLC scenario as a guide. Can you spot the issue in the following output:r3#
03:03:49: IP-EIGRP: Neighbor 192.168.9.18 not on common subnet for Serial0/3
03:04:03: IP-EIGRP: Neighbor 192.168.9.18 not on common subnet for Serial0/3
03:04:18: IP-EIGRP: Neighbor 192.168.9.18 not on common subnet for Serial0/3
03:04:32: IP-EIGRP: Neighbor 192.168.9.18 not on common subnet for Serial0/3
r5#show ip interface brief
Interface IP-Address OK? Method Status Protocol
BRI0 unassigned YES unset administratively down down
BRI0:1 unassigned YES unset administratively down down
BRI0:2 unassigned YES unset administratively down down
Ethernet0 unassigned YES unset administratively down down
Loopback8 5.5.5.5 YES manual up up
Serial0 192.168.9.18 YES manual up up
Serial0.101 172.16.8.6 YES manual deleted down
Serial1 unassigned YES unset administratively down down
r5#
03:04:01: IP-EIGRP: Neighbor 192.168.9.13 not on common subnet for Serial0
03:04:15: IP-EIGRP: Neighbor 192.168.9.13 not on common subnet for Serial0
03:04:29: IP-EIGRP: Neighbor 192.168.9.13 not on common subnet for Serial0
|
| A6: | Answer: s0 was configured for .18 rather than .14. Obviously both ends of a wire must be on the same subnet:
r5#configure terminal r5(config)#interface s1 r5(config-if)#shut 03:04:43: IP-EIGRP: Neighbor 192.168.9.13 not on common subnet for Serial0 r5(config-if)#encapsulation hdlc r5(config-if)#ip address 192.168.9.18 255.255.255.2 03:04:57: IP-EIGRP: Neighbor 192.168.9.13 not on common subnet for Serial052 r5(config-if)#no shut r5(config-if)#end r5#show ip interface brief 03:05:04: %SYS-5-CONFIG_I: Configured from console by console 03:05:05: %LINK-3-UPDOWN: Interface Serial1, changed state to up Interface IP-Address OK? Method Status Protocol BRI0 unassigned YES unset administratively down down BRI0:1 unassigned YES unset administratively down down BRI0:2 unassigned YES unset administratively down down Ethernet0 unassigned YES unset administratively down down Loopback8 5.5.5.5 YES manual up up Serial0 192.168.9.14 YES manual up up Serial0.101 172.16.8.6 YES manual deleted down Serial1 unassigned YES unset administratively down down |
| 7: | Throughout the chapter you experienced multiple carrier transitions. What command is very helpful in helping you figure out the issues with this problem? |
| A7: | Answer: To assist with finding the issues related to carrier transitions, you should target the lower layers. First, look at show interfaces, and controllers may be of some help. You can watch the actual keepalive activity with the debug serial interface command. |
| 8: | You have a high-speed Ethernet that is sending packets faster than the ISDN link can keep up with. How can you improve performance? |
| A8: | Answer: There are many ways to improve performance. You could try bringing up the second B channel for ISDN. If necessary you can disable fast switching. |
| 9: | When are floating static routes appropriate? |
| A9: | Answer: Floating statics are used as a backup static route to a routing protocol. The administrative distance is set higher than the routing protocol so that the floating static is not used unless the routing protocol entry is not in the table. |
| 10: | When using the backup interface method to back up a circuit, do you place the backup interface command under the primary or secondary interface? |
| A10: | Answer: The backup interface command goes under the primary interface configuration. Refer to Example 9-31. |
| 11: | You are controlling the backup interface using the backup delay 10 60 command. What do the numbers 10 and 60 correspond to? |
| A11: | Answer: The backup delay 10 60 command says that the backup link will be up 10 seconds after the primary link fails and the backup link will go down 60 seconds after the primary comes back up. |
| 12: | Your ISDN phone bill is a lot more than you expected, but you have interesting traffic set appropriately with an access list. It seems that when you finish transferring your files over the ISDN link, the link doesn't go down. It stays up until you manually bring it down. What did you forget? |
| A12: | Answer: Configure the dialer idle-timeout command. |
| 13: | Including synchronization and framing, what is the total bandwidth for ISDN BRI? |
| A13: | Answer: There are two B channels that are 64 kbps each, which equals 128 kbps. Add the D channel at 16 kbps to give you 144 kbps. Add the 48 kbps for synchronization and framing for a total of 192 kbps. |
| 14: | Can you use one 64 kbps B channel to handle backup for multiple T1s? |
| A14: | Answer: Yes, you can you use one 64-kbps B channel to handle backup for multiple T1s by way of dialer profiles. Dialer profiles give you this type of flexibility by separating the logical configurations from the physical interfaces. |
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