| Date of Issue: 08-01-2023 | Rate this Study Guide |
Question 1.
While troubleshooting a Frame Relay problem, you enter the show running-config command on a local router. Then you compare the output with the configuration of a router at the other end of the PVC. What will you do if you discover that the two routers are using different LMI types?
| a) | Use the show frame-relay pvc command to ensure that the routers are able to send data to each other despite the inconsistency |
| b) | Configure the local CSU/DSUs for loopback testing to isolate the cause of the inconsistency |
| c) | Look elsewhere for the source of the problem, as this is a legitimate configuration and probably unrelated to the problem |
| d) | Call TAC to report the problem as it is probably related to a Cisco IOS bug |
| e) | Ask the service provider to put its local switches into loopback mode to ensure that LMI is working correctly despite the inconsistency |
Question 2.
Which statements are true about the following Cisco router output?
RX <- SETUP pd = 8 callref = 0x06 Bearer Capability i = 0x8890 Channel ID i = 0x89 Calling Party Number i = 0x0083, \Q5551234' TX -> CONNECT pd = 8 callref = 0x86 RX <- CONNECT_ACK pd = 8 callref = 0x06
| a) | This output resulted from entering the debug isdn q931 command |
| b) | This output resulted from entering the debug frame-relay lmi command |
| c) | The first line of output indicates that a connection is being initiated by the remote end |
| d) | This output represents a successful ISDN Layer 3 connection establishment |
| e) | This output resulted from entering the debug isdn q921 command |
Question 3.
When might you use a breakout box to troubleshoot a WAN problem?
| a) | To investigate problems connecting a CSU/DSU to the serial interface on a Cisco router when the interface is down/down |
| b) | To analyze packets crossing a WAN circuit |
| c) | To investigate problems with a CSU/DSU communicating with the provider's switch in the provider's Central Office |
| d) | To investigate problems connecting a CSU/DSU to the serial interface on a Cisco router when the interface is up/down |
Answers
Question 1.
While troubleshooting a Frame Relay problem, you enter the show running-config command on a local router. Then you compare the output with the configuration of a router at the other end of the PVC. What will you do if you discover that the two routers are using different LMI types?
| a) | Use the show frame-relay pvc command to ensure that the routers are able to send data to each other despite the inconsistency |
| b) | Configure the local CSU/DSUs for loopback testing to isolate the cause of the inconsistency |
| c) | Look elsewhere for the source of the problem, as this is a legitimate configuration and probably unrelated to the problem |
| d) | Call TAC to report the problem as it is probably related to a Cisco IOS bug |
| e) | Ask the service provider to put its local switches into loopback mode to ensure that LMI is working correctly despite the inconsistency |
| c) | Look elsewhere for the source of the problem, as this is a legitimate configuration and probably unrelated to the problem |
Explanation
Local Management Interface (LMI) runs between the router and the local switch. The routers at either end of the Permanent Virtual Circuit (PVC) don't need to agree on the LMI type. Each router needs to agree only with its local switch. Because this is unlikely to be the cause of the problem, you wouldn't go to the effort of putting the circuit into loopback mode until you have gathered more facts about the problem.
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Question 2.
Which statements are true about the following Cisco router output?
RX <- SETUP pd = 8 callref = 0x06 Bearer Capability i = 0x8890 Channel ID i = 0x89 Calling Party Number i = 0x0083, \Q5551234' TX -> CONNECT pd = 8 callref = 0x86 RX <- CONNECT_ACK pd = 8 callref = 0x06
| a) | This output resulted from entering the debug isdn q931 command |
| b) | This output resulted from entering the debug frame-relay lmi command |
| c) | The first line of output indicates that a connection is being initiated by the remote end |
| d) | This output represents a successful ISDN Layer 3 connection establishment |
| e) | This output resulted from entering the debug isdn q921 command |
| a) | This output resulted from entering the debug isdn q931 command |
| c) | The first line of output indicates that a connection is being initiated by the remote end |
| d) | This output represents a successful ISDN Layer 3 connection establishment |
Explanation
Integrated Services Digital Network (ISDN) Layer 3 is implemented by Q.931, which you can analyze with the debug isdn q931 command, as shown in the example. Q.931 handles end-to-end connection establishment with commands such as SETUP, CALL PROCEEDING, and CONNECT. The fact that the output shows a CONNECT_ACK is a good sign. It appears that the connection has been established successfully. Data flow should follow.
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Question 3.
When might you use a breakout box to troubleshoot a WAN problem?
| a) | To investigate problems connecting a CSU/DSU to the serial interface on a Cisco router when the interface is down/down |
| b) | To analyze packets crossing a WAN circuit |
| c) | To investigate problems with a CSU/DSU communicating with the provider's switch in the provider's Central Office |
| d) | To investigate problems connecting a CSU/DSU to the serial interface on a Cisco router when the interface is up/down |
| a) | To investigate problems connecting a CSU/DSU to the serial interface on a Cisco router when the interface is down/down |
Explanation
According to Cisco, you can insert a breakout box to check the low-level signaling between a Channel Service Unit/Digital Service Unit (CSU/DSU) and the router when the router serial interface is down/down.
A breakout box is a handheld device that analyzes the signals carried on synchronous serial interfaces. Because modern CSU/DSUs act more like DSUs than CSUs, the data is presented to the Data Terminal Equipment (DTE) router over a synchronous V.35 link. This means that you can investigate V.35 signals such as Data Carrier Detect (DCD or CD), Data Set Ready (DSR), and Clear to Send (CTS) from the DSU side; and Data Terminal Ready (DTR) and Request to Send (RTS) from the router side. (The use of a breakout box to troubleshoot a serial problem is usually a last resort these days. Easier methods, such as swapping the cable or moving the cable to a different serial interface, should be the first troubleshooting steps.)
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