5.6.6 Packet Tracer – Troubleshoot Common Network Problems (Answers)
|Device||Interface||IPv4 Address||Subnet Mask||Default Gateway|
|DEVASC Server||NIC||IN: 192.168.2.3||255.255.255.0||192.168.1.1|
- Part 1: Test connectivity
- Part 2: Troubleshoot R3
- Part 3: Troubleshoot R1
- Part 4: Troubleshoot DNS
Background / Scenario
Networks have a lot of components working together to ensure connectivity and data delivery. Often, these components may not work properly. This may be due to a simple device misconfiguration, or many, seemingly unrelated problems that must be systematically resolved. As a developer, you may need to troubleshoot network issues to regain connectivity. To troubleshoot network issues, it is necessary to take a step-by-step methodical approach, using clues to determine the problem and implement a solution. You may often find more than one problem preventing a connection from working.
Note: In this activity, the two web servers are referred to as DEVASC Server and Example Server. In the topology, they are named with their URL: www.devasc-netacad.pka and www.example.com.
Part 1: Test Connectivity
In this Part, you are on PC-B, trying to reach the web page of the DEVASC Server.
Step 1: Test the connectivity of the network.
a. Click PC-B.
b. Click Desktop.
c. Click Web Browser.
d. Enter www.devasc-netacad.pka in the URL field and click Go.
The web page request will not work. There may be one or many different problems between PC-B and the server. We will begin troubleshooting from PC-B and work our way over to the server, troubleshooting along the way.
Step 2: Troubleshoot the basic configuration of PC-B.
In the Packet Tracer work area, you can see that the connection between PC-B and S3 has red icons. This means that the connection is physically down between the two or TCP/IP is not correctly configured on PC-B. Begin by troubleshooting the protocol stack first.
a. Click PC-B.
b. Close the Web Browser, if it is open.
c. Click Command Prompt.
d. Ping the loopback address to ensure that TCP/IP is installed and working properly.
Pinging 127.0.0.1 with 32 bytes of data: Reply from 127.0.0.1: bytes=32 time=3ms TTL=128 Reply from 127.0.0.1: bytes=32 time=16ms TTL=128 Reply from 127.0.0.1: bytes=32 time=3ms TTL=128 Reply from 127.0.0.1: bytes=32 time=3ms TTL=128 Ping statistics for 127.0.0.1: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 3ms, Maximum = 16ms, Average = 6ms C:\>
Because there were successful replies, we know that TCP/IP is installed and working correctly. This means that, most likely, either the Ethernet port on PC-B or S3 is not enabled.
e. Click Config on PC-B.
f. Click FastEthernet0.
g. The Port Status is Off. Click On next to Port Status to enable the interface.
Notice the icons between PC-B and S3 turn green after a few seconds to indicate communication between the two devices.
h. Click Desktop.
i. Close the Command Prompt window.
Step 3: Check the IP configuration.
a. Click IP Configuration.
b. You should be provided with an IP address if there is a DHCP server on the network.
Notice that the DHCP request failed. Because PC-B cannot reach a DHCP server, you will need to provide static IP address information.
c. Click the radio button next to Static to assign the interface IP Configuration information:
IP Address: 172.16.3.2
Subnet Mask: 255.255.255.0
Default Gateway: 172.16.3.1
DNS Server: 220.127.116.11
You now have the correct information to get to the default gateway.
d. Close IP Configuration and click Web Browser.
e. Enter www.devasc-netacad.pka in the URL field and click Go.
Again, the request fails.
Part 2: Troubleshoot R3
In this Part, you will test connectivity to the next network device, R3, to continue troubleshooting.
Step 1: Communicate with the default gateway.
a. Close the Web Browser, if it is open.
b. Click Command Prompt.
c. Ping the default gateway.
C:\>ping 172.16.3.1 Pinging 172.16.3.1 with 32 bytes of data: Request timed out. Request timed out. Request timed out. Request timed out. Ping statistics for 172.16.3.1: Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), C:\>
You know that the IP addressing information on PC-B is correct, that the interface is up, and that the TCP/IP stack is working properly. There must be something wrong with the default gateway preventing communication.
Step 2: Check the IP configuration of R3.
a. Click R3.
b. Click Config.
c. Click GigabitEthernet0/0/1. This is the interface connected to the 172.16.3.0/24 network.
The interface is up, and there is IP addressing information for it, but it is not correct for the 172.16.3.0 network.
d. Change the IP address for the interface to 172.16.3.1.
Step 3: Check connectivity.
a. Return to PC-B and ping the default gateway again to ensure communication is working between the devices.
C:\>ping 172.16.3.1 Pinging 172.16.3.1 with 32 bytes of data: Reply from 172.16.3.1: bytes=32 time<1ms TTL=255 Reply from 172.16.3.1: bytes=32 time<1ms TTL=255 Reply from 172.16.3.1: bytes=32 time=2ms TTL=255 Reply from 172.16.3.1: bytes=32 time<1ms TTL=255 Ping statistics for 172.16.3.1: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 2ms, Average = 0ms C:\>
Great! We now have communication between PC-B and the default gateway.
b. Return to the Web Browser on PC-B and attempt to connect to the www.devasc-netacad.pka web page on the DEVASC Server again.
It still does not work.
Part 3: Troubleshoot R1
In this Part, you will continue troubleshooting on the next device in the path, R1, because you do not have any control over the devices in the Internet cloud.
Step 1: Check the basic configuration of R1.
By looking at the Packet Tracer work area, we can see that there is a physical problem with the cabling between R1 and FIREWALL.
a. Click R1, and then the Config tab.
b. Check the Port Status of each interface.
The ports are up.
The network between the devices is 18.104.22.168/29. The IP addresses of the ports at either end of the cable must fall in this range for communication to take place.
Step 2: Check the cable.
a. Hover over FIREWALL.
VLAN2 has an acceptable IP address, and the link is up.
b. Hover over R1.
G0/0/0 has an acceptable IP address, and the link is up. The problem is the cable itself. It may be damaged, or it may be connected to an incorrect port.
You will need to re-cable the connection between the devices.
Step 3: Replace the cable.
a. Be sure to click any white space in the topology to de-select any devices that may be currently selected. Then use the Delete tool to remove the cable between R1 and FIREWALL.
b. Click Connections.
c. Click the Copper Straight-Through cable, and then click FIREWALL.
d. Choose Ethernet0/0 as the connection. This is the port assigned to 22.214.171.124/29 (VLAN1).
e. Click R1.
f. Choose port GigabitEthernet0/0/0. This is the port assigned to 126.96.36.199/29.
You should now see icons on both sides of the cable, and soon they turn green.
Step 4: Check connectivity.
a. Return to the Web Browser on PC-B and attempt to bring up the DEVASC server web page.
It still does not work. To find out if it is a connection issue or a protocol issue, attempt to ping the DEVASC Server IP address.
b. Return to the Command Prompt.
c. Ping the IP address of the DEVASC Server. In Packet Tracer, the first set of pings may fail until the network converges.
C:\> ping 188.8.131.52 Pinging 184.108.40.206 with 32 bytes of data: Request timed out. Request timed out. Request timed out. Request timed out. Ping statistics for 220.127.116.11: Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), C:\> ping 18.104.22.168 Pinging 22.214.171.124 with 32 bytes of data: Reply from 126.96.36.199: bytes=32 time<1ms TTL=253 Reply from 188.8.131.52: bytes=32 time=1ms TTL=253 Reply from 184.108.40.206: bytes=32 time<1ms TTL=253 Reply from 220.127.116.11: bytes=32 time<1ms TTL=253 Ping statistics for 18.104.22.168: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 1ms, Average = 0ms C:\>
This is what you wanted to see. We are getting all the way to the DEVASC Server, and all the way back using ICMP. This tells you there may be something wrong with the DNS configuration.
Part 4: Troubleshoot DNS
Because there is connectivity from PC-B to the DEVASC Server using ICMP, you know all the physical problems and configuration problems preventing connections before have been solved. This means there is most likely a protocol issue preventing the web page from displaying.
a. Open the Web Browser on PC-B.
b. Type the IP address of the DEVASC server, along with the port to which you would like to connect: 80.
You will receive a response from the server.
The web page does not respond to port 80. In a previous lab, the server was configured to only connect using secure HTTP (HTTPS). This was to make sure that the FIREWALL does not forwarding traffic on the unencrypted port 80. You need to use HTTPS to connect to the web page:
After a few seconds, the web page finally displays!
The most likely problem is the DNS configuration.
Step 2: Verify DNS.
a. On PC-B, open IP Configuration.
b. Ensure the DNS Server is set to 22.214.171.124.
c. Since it is correctly configured, check the configuration of the DNS settings on the Example Server.
Step 3: Verify DNS server configuration.
a. Click the Example Server.
b. Click Services.
c. Click DNS.
There are no DNS records and the service is disabled.
d. Add an entry for the DEVASC Server with the Name set to www.devasc-netacad.pka and Address set to 126.96.36.199. Then click Add.
Even though the entry is now correct, DNS has not been turned on.
e. Turn On DNS.
f. Return to PC-B, open a Web Browser, and type https://www.devasc-netacad.pka in the URL field. Be sure you add https:// as FIREWALL only allows secure web traffic.
You will now see that the web page is accessible using DNS across the network.
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