Network Troubleshooting - sullivaneg/TechJournal-NET150 GitHub Wiki
Introduction
In this lab I was given 5 challenges with associated packet tracer files. The goal was to troubleshoot my way to finding the problem in the network. I was to apply the principles of troubleshooting we were taught and start with a specific method.
Challenge 1
Foster Laptop should be able to ping Skiff Laptop - but something is wrong! Pick one of the Troubleshooting Methods to start troubleshooting. Take notes of what you try. Solve the problem
Description of Troubleshooting Approach you started with and the steps your took
- I just started by checking to make sure the foster laptop really couldn’t ping skiff laptop. It failed.
- I started with a divide and conquer approach because there are 2 sides.
- I checked to make sure the foster laptop could ping the router. This was successful.
- Then I checked if the skiff laptop could ping the router. That was successful.
- So both sides could ping the router.
- Then I went in and checked that the router had two default gateway IP addresses and double checked that each other computers had the default gateway IP address correct and that their own IP was in the same network as the default gateway.
- I found that the Skiff laptop didn’t have a default gateway put into it’s settings.
- I corrected this by putting 192.168.1.1 in for the default gateway since that was the IP of the Fa0/1 interface which the Skiff switch was connected to.
- Then I tried to ping from the Foster Laptop to the Skiff laptop again and it was successful.
Description of any issues you encountered, mistakes you made, whether another approach would have been better and/or did you combine methods
I didn’t really run into any issues with this challenge, I also didn’t really combine methods for this one because it was a pretty small network.
Screenshot of successful ping between Foster Laptop and Skiff Laptop
Challenge 2
Once again - Foster Laptop should be able to ping Skiff Laptop - but something different is wrong! Pick one of the Troubleshooting Methods to start troubleshooting. Take notes of what you try. Solve the problem.
Description of Troubleshooting Approach you started with and the steps you took
- Right away I noticed that one of my wires has the red triangles above them. I still decided to start by dividing and conquering just because I don’t think in a real life scenario there would be those red triangles.
- Ping from Foster Laptop to CNCS Router: Successful
- Double checked Foster Laptop’s config and the CNCS Router config on the Fa0/0 interface because that is the interface that was connected to the Foster Switch: No problems found
- Ping from Skiff Laptop to CNCS Router: Failed
- Double checked Skiff Laptop’s config and the CNCS Router config on the Fa0/1 interface because that is the interface that was connected to the Foster Switch: There was no IPv4 address put in for the Fa0/1 interface.
- I put in 192.168.1.1 for the IPv4 address
- I tried to ping from Skiff laptop to the CNCS router again: Failed
- I went back to the Router and turned on the Fa0/1 interface.
- I tried to ping from Skiff laptop to the CNCS router again: Successful
- I tried to ping from Foster Laptop to Skiff laptop: Successful
Description of any issues you encountered, mistakes you made, whether another approach would have been better and/or did you combine methods
I didn’t run into any issues with this challenge either. I’m not sure if another approach would have worked better. I liked dividing and conquering because it helped me narrow down where the problem could have come from and then I can check the config on that side. With a bigger network dividing and conquering wouldn’t be enough to super narrow down where the problem is coming from, so for a bigger network I could see combining divide and conquer with following the path to figure out where the broken link is. One mistake I almost made in this lab was thinking that me putting the IPv4 address in wasn’t enough to fix the network but really it was I just also had to turn on the interface.
Screenshot of successful ping between Foster Laptop and Skiff Laptop
Challenge 3
PC0, PC1, PC2, PC3 should all be able to ping PC4. Pick one of the Troubleshooting Methods to start troubleshooting. Take notes of what you try. Solve the problem.
Description of Troubleshooting Approach you started with and the steps your took
- I started with a divide and conquer approach and also I guess it could be considered following the path.
- Ping PC0 to Router: Failed
- Ping PC1 to Router: Failed
- Ping PC2 to Router: Failed
- Ping PC3 to Router: Failed
- Ping Router to PC4/PC4 to Router: Failed
- So the problem is on both sides. So I started with examining the Router’s configuration and making sure that everything was turned on and that the interfaces matched with the PC’s default gateways.
- Fa0/0: 10.10.10.1 which is the interface that the 20.20.20.0/24 network is connected to.
- Fa0/1 20.20.20.1 which is the interface that the 10.10.10.0/24 network is connected to.
- All of the PCs in the 10.10.10.0/24 network had 10.10.10.1 as their default gateway and appropriate IP addresses in their network.
- I rewired from the 10.10.10.0 switch to the CNCS router 0/1 port.
- I rewired from the 20.20.20.0 switch to the CNCS router 0/0 port.
- Ping from PC0 to PC4: Failed
- I’m going to start my following the path again to see if the problem is still in the same place:
- Ping PC0 to Router: Successful
- Ping PC1 to Router: Successful
- Ping PC2 to Router: Successful
- Ping PC3 to Router: Successful
- Ping Router to PC4/PC4 to Router: Successful
- Because both sides were successful I’m going to try pinging across again. I think I might not have given enough time:
- Ping from PC0-PC4: Successful
- Ping from PC1-PC4: Successful
- Ping from PC2-PC4: Successful
- Ping from PC3-PC4: Successful
Description of any issues you encountered, mistakes you made, whether another approach would have been better and/or did you combine methods
One issue I encountered that I keep running into in labs and forgetting that it’s an issue is the first ping not being successful. In this lab my pings weren’t successful so I thought something was wrong and I went back to the beginning with the divide and conquer approach, when in reality I just hadn’t left enough time or pinged again. I did that and saw that my network was working again. In this lab I combined divide and conquer with follow the path to narrow down where in my network the problem is.
Screenshot of successful ping between the 10.10.10.0/24 and 20.20.20.0/24 network PC's
Challenge 4
PC0, PC1 should be able to ping PC2. Pick one of the Troubleshooting Methods to start troubleshooting. Take notes of what you try. Solve the problem.
Description of Troubleshooting Approach you started with and the steps you took
- I started with a follow the path approach since there are multiple routers and I wanted to narrow down where the problem was occurring
- Ping PC0 to Router 1: Successful
- Ping PC1 to Router 1: Successful
- Ping Router 1 to Router 2: Successful
- Ping Router 2 to Router 3: Successful
- Ping Router 3 to PC2: Failed
- So I narrowed down that the problem is happening from Router 3 to PC2: I opened the config on PC2 and Router 3 to make sure that everything was put in correctly
- PC2: Default Gateway: 192.168.10.193, Subnet Mask: 255.255.255.192, IPv4 address: 192.168.10.194
- Router 3: IPv4 address: 192.168.10.193, Subnet Mask: 255.255.255.192
- It all seemed to match up so I tried pinging again just to make sure
- Ping from PC2 to Router 3: Successful
- Ping from Router 3 to PC 2: Successful
- So now I needed to use a new approach because every part of the follow the path was successful until I tried to ping from PC0 to PC2. I don’t know if this is a legit troubleshooting method but I’m going to adjust my follow the path so that instead of moving from one hop to another I’m going to increase the path from PC0 and PC1 by 1 hop until I see where the problem is.
- PC0 to PC2:
- PC0 to Router 1: Successful
- PC0 to Router 2: Successful
- PC0 to Router 3: Failed
- PC0 to PC2: Failed
- PC1 to PC2:
- PC0 to Router 1: Successful
- PC0 to Router 2: Successful
- PC0 to Router 3: Failed
- PC0 to PC2: Failed
- With this information I came up with a hypothesis there’s an issue with the static routing. Because I can reach Router 1 and 2 from PC0 and PC1 and I can reach router 3 from router 2, I’m hypothesizing that Router 1 doesn’t know the route to Router 3 or Router 3 doesn’t know the route to Router 1.
- I inspected all of the static routes and Router 3 is missing the route to Router 1’s network. I added the following static route:
- Ping PC1 to PC2: Successful
Description of any issues you encountered, mistakes you made, whether another approach would have been better and/or did you combine methods
I wrote about this in my description of my steps but I started with follow the path and then all of my segments were successful. So I did kind of an adapted version where I added one more section of the path each attempt to see if there was a problem with the static routing, because all of the routers knew about each other so they could ping each other, but one of the routers didn’t know about the route to PC0 so this method worked to show me that the ping was failing from the PC. I guess the only issue I ran into was a roadblock when my initial approach came back with no information, but I figured it out.
Screenshot of successful ping between PC1 and PC2
Challenge 5
All PC's should be able to ping each other - but something is wrong! Pick one of the Troubleshooting Methods to start troubleshooting. Take notes of what you try. Solve the problem.
Description of Troubleshooting Approach you started with and the steps you took
- I’m going to use a top down approach I think. The highest level we have is pinging between devices using switches so we start in level 2.
- Ping Clinic PC1 to
- Guest Laptop 1: Failed
- Clinic PC2: Successful
- Guest laptop 2: Failed
- Ping Guest Laptop 1:
- Clinic PC1: Failed
- Clinic PC2: Failed
- Guest laptop 2: Failed
- Ping Guest Laptop 2:
- Clinic PC1: Successful
- Clinic PC2: Failed
- Guest laptop 1: Failed
- Ping Clinic PC2 to
- Guest Laptop 1: Successful
- Clinic PC1: Successful
- Guest laptop 2: Failed
- It looks like we have a VLAN set up here with the Clinic PC’s and the Guest Laptops on different VLANs. I’m going to trace the path but instead of pinging I’m just going to check the physical connection from each computer to the switches and make sure the ports are correct and they are within the same VLAN. Since we can’t have success on Level 2 we are going to go down to Level 1 and check the physical connections. We can’t ping across VLANS or within them for some of the devices.
- Clinic PC1: Fa0 connects to Fa0/2 of the 1st floor switch
- Fa0/2: is an access port with VLAN 10 which is the Clinic VLAN. This connection is correct.
- Guest Laptop 1: Fa0 connects to Fa0/15 of the 1st floor switch.
- Fa 0/15: is an access port on VLAN 20 which is the Guest VLAN. This connection is correct.
- Clinic PC2: Fa0 is connected to Fa0/2 of the 2nd floor switch
- Fa0/2: is an access port on VLAN 10. This connection is correct.
- Guest Laptop 2: Fa0 is connected to Fa0/15 on the 2nd floor switch.
- Fa0/15 is an access port for VLAN 1. This is incorrect. I’m going to change it to an access port for VLAN 20.
- Try pinging again before I continue troubleshooting:
- Ping Clinic PC1 to
- Guest Laptop 1: Successful (changed since first attempt)
- Clinic PC2: Successful
- Guest laptop 2: Failed
- Ping Guest Laptop 1:
- Clinic PC1: Successful (changed since first attempt)
- Clinic PC2: Successful (changed since first attempt)
- Guest laptop 2: Failed
- Ping Guest Laptop 2:
- Clinic PC1: Failed (changed since first attempt)
- Clinic PC2: Failed
- Guest laptop 1: Failed
- Ping Clinic PC2 to
- Guest Laptop 1: Successful
- Clinic PC1: Successful
- Guest laptop 2: Failed
- There were some changes but nothing can ping laptop 2. I’m going to continue troubleshooting. I’m going to check the connection between the 1st floor and 2nd floor switches.
- First floor switch Gig0/1 is connected to 2nd floor switch Gig0/1
- First floor Gig0/1: Trunk port for both VLANS
- Second Floor Gig0/1: Trunk Port for both VLANS
- That connection was correct so now I”m going to check the multilayer switch.
- Multilayer switch VLAN database has both VLANS
- Multilayer switch is connected gig0/2 to 2nd floor switch gig0/2
- Multilayer switch gig0/2: Trunk port for both VLANS
- 2nd floor switch gig0/2: Also a trunk port for both VLANS.
- All of the physical connections are correct.
- So I thought maybe the problem was that you couldn’t use a multilayer switch to ping across VLANS so I disconnected the wire from the Multilayer switch to the second floor switch. Then I realized that you should be able to use it because it’s level 3 so I replugged the multilayer switch from gig0/2 to gig0/2. And then as an attempt to kind of get my bearings because I got lost here I tried all my pings again and they worked so I don’t really know what happened.
- Ping Clinic PC1 to
- Guest Laptop 1: Successful
- Clinic PC2: Successful
- Guest laptop 2: Successful (changed since first attempt)
- Ping Guest Laptop 1:
- Clinic PC1: Successful (changed since first attempt)
- Clinic PC2: Successful (changed since first attempt)
- Guest laptop 2: Successful (changed since first attempt)
- Ping Guest Laptop 2:
- Clinic PC1: Successful (changed since first attempt)
- Clinic PC2: Successful (changed since first attempt)
- Guest laptop 1: Successful (changed since first attempt)
- Ping Clinic PC2 to
- Guest Laptop 1: Successful
- Clinic PC1: Successful
- Guest laptop 2: Successful (changed since first attempt)
Description of any issues you encountered, mistakes you made, whether another approach would have been better and/or did you combine methods
I checked through everything. I’m not really sure what the problem was but it was something to do with the connection to the multilayer switch because when I disconnected it and reconnected it, everything worked. I talked about some of the mistakes I made in the above section.