Last Updated on April 26, 2018 by Admin
2.1.2.5 Packet Tracer – Troubleshooting Serial Interfaces
Packet Tracer – Troubleshooting Serial Interfaces (Answer Version)
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Topology
2.1.2.5 Packet Tracer – Troubleshooting Serial Interfaces
Addressing Table
| Device | Interface | IP Address | Subnet Mask | Default Route |
| Telco | S0/0/0 (DCE) | 64.100.34.17 | 255.255.255.252 | N/A |
| S0/0/1 (DCE) | 64.100.34.21 | 255.255.255.252 | N/A | |
| S0/1/0 (DCE) | 64.100.34.25 | 255.255.255.252 | N/A | |
| S0/1/1 (DCE) | 64.100.34.29 | 255.255.255.252 | N/A | |
| R1 | S0/0/0 | 64.100.34.18 | 255.255.255.252 | 64.100.34.17 |
| R2 | S0/0/1 | 64.100.34.22 | 255.255.255.252 | 64.100.34.21 |
| R3 | S0/0/0 | 64.100.34.26 | 255.255.255.252 | 64.100.34.25 |
| R4 | S0/0/1 | 64.100.34.30 | 255.255.255.252 | 64.100.34.29 |
Objectives
Part 1: Diagnose and Repair the Physical Layer
Part 2: Diagnose and Repair the Data Link Layer
Part 3: Diagnose and Repair the Network Layer
Scenario
You have been asked to troubleshoot WAN connections for a local telephone company (Telco). The Telco router should communicate with four remote sites, but none of them are working. Use your knowledge of the OSI model and a few general rules to identify and repair the errors in the network.
Part 1: Diagnose and Repair the Physical Layer
Step 1: Diagnose and repair the cabling.
- Examine the Addressing Table to determine the location of the DCE connections.
- Each serial connection has a DCE and a DTE connection. To determine if each Telco interface is using the correct end of the cable look on the third line of output following the show controllers command.
- Telco# show controllers [interface_type interface_num]
- Reverse any cables that are incorrectly connected.
Note: Cable between Telco and R4 should be reversed and clock rate set on Telco. Serial Cable on R4 should connect to S0/0/1.
Note: In real network settings, the DCE (which sets the clock rate) is typically a CSU/DSU.
Step 2: Diagnose and repair incorrect port connections.
- Examine the Addressing Table to match each router port with the correct Telco port.
- Hold the mouse over each wire to ensure that the wires are connected as specified. If not, correct the connections.
Step 3: Diagnose and repair ports that are shutdown.
- Show a brief interface summary of each router. Ensure that all of the ports that should be working are not administratively down.
- Enable the appropriate ports that are administratively down:
R3(config)# interface s0/0/0 R3(config-if)# no shutdown
Part 1: Diagnose and Repair the Data Link Layer
Step 1: Examine and set clock rates on DCE equipment.
- All of the DCE cables should be connected to Telco. Show the running configuration of Telco to verify that a clock rate has been set on each interface.
- Set the clock rate of any serial interfaces that requires it:
Telco(config)# interface s0/0/0 Telco(config-if)# clock rate 4000000 Telco(config-if)# interface s0/1/1 Telco(config-if)# clock rate 4000000
Step 2: Examine the encapsulation on DCE equipment.
- All of the serial interfaces should be using HDLC as the encapsulation type. Examine the protocol setting of the serial interfaces.
- Telco# show interface [interface_type interface_num]
- Change the encapsulation type to HDLC for any interface that is set otherwise:
R4(config)# interface s0/0/1 R4(config-if)# encapsulation hdlc
Part 3: Diagnose and Repair the Network Layer
Step 1: Verify the IP addressing.
- Show a brief interface summary of each router. Check the IP addresses against the Addressing Table and ensure that they are in the correct subnet with their connecting interface.
- Correct any IP addresses that overlap, or are set to the host or broadcast address:
R1(config)# interface s0/0/0 R1(config-if)# ip address 64.100.34.18 255.255.255.252