Welcome to Jeremy’s IT Lab. This is a free, complete course for the CCNA. If you like these videos, please subscribe to follow along with the series. Also, please like and leave a comment, and share the video to help spread this free series of videos. Thanks for your help. You may recognize this network topology. This is the same network we configured in the previous lab. However, this time there are a few configuration errors, so PC1 and PC2 are unable to ping each other. As the lab instructions say, there is one misconfiguration per router, so we have to find and fix the misconfigurations. Troubleshooting labs like this are great practice for the CCNA. Troubleshooting helps test your knowledge of the concepts, and troubleshooting questions may also appear on the CCNA exam itself. I highly recommend you try to complete this lab yourself first, if you watch the video before you will already know what the problems in the network are and you won’t practice your own troubleshooting skills. Okay, before we get started troubleshooting, we should confirm the problem. PC1 and PC2 should not be able to ping eachother. I’ll go on PC1 and try to ping PC2. Okay, let’s send that ping. Ping 192.168.3.1. Okay, the ping indeed does not work. Although the misconfigurations are on the routers in this lab, let’s quickly check the PC’s configuration. To check the configuration on a windows PC, use the command IPCONFIG. Here you can see the IP address, subnet mask, and default gateway. If you want more detail, use the command IPCONFIG /ALL. This gives more information, such as the physical address. What is the physical address? Well, it’s the MAC address. Okay, let’s see if we can ping the default gateway, since to reach other networks we need to be able to reach the default gateway. PING 192.168.1.254. Okay, no problems here. Let’s go on R1 now and see if we can find the issue...enter privileged exec mode with ENABLE. First I’ll check if the interface configuration is okay. SHOW IP INTERFACE BRIEF...the addresses are correct, and both interfaces are UP/UP, so the interface configuration is fine. Let’s check the routing table. SHOW IP ROUTE...here’s the static route for the 192.168.3.0/24 network, but can you see the misconfiguration? It says via 192.168.12.3, but actually the next hop address should be 192.168.12.2, which is the IP address of R2’s G0/0 interface. Let’s check it in the running config. Show running-config, and then I’m going to filter the output by using the PIPE symbol, INCLUDE, and then ip route. Here you can see the configuration statement. I’m going to right click to copy it, and then go to global config mode. CONFIGURE TERMINAL. Now I’ll paste in the configuration statement, and use the keyboard shortcut CTRL+A to go to the beginning of the line. Type NO, followed by a space, and then hit enter. and that deletes the configuration statement. Let’s check. DO SHOW RUNNING-CONFIG, PIPE, INCLUDE IP ROUTE. Okay, it’s gone. Now I’ll paste in the configuration statement once more, and change this 3 to a 2. I’ll use the up arrows to go back to the show running-config command, and now you can see we have the correct configuration statement. Let’s check the routing table one last time. DO SHOW IP ROUTE. Okay, there’s the correct route. So, we have fixed the problem on R1. Now let’s move on to R2. Enter privileged exec mode with ENABLE. And let’s check the interface configuration. SHOW IP INTERFACE BRIEF. The IP addresses both are correct, and the interfaces are UP/UP, so no problems here. Let’s check the routing table. SHOW IP ROUTE. We have two static routes as expected, 192.168.1.0/24 via 192.168.12.1 is correct. And 192.168.3.0/24, with an exit interface of gigabitethernet0/0, there’s our problem. To reach the 192.168.3.0/24 network, R2 should use the gigabitethernet0/1 interface, not 0/0. Let’s see what happens if I enter the correct route without removing the incorrect one. CONFIGURE TERMINAL. IP ROUTE 192.168.3.0 255.255.255.0 g0/1. DO SHOW IP ROUTE. Okay, you can see both routes are kept in the routing table, the second does not override the first. Because both are in the routing table, this means the router will ‘load-balance’ over the two routes, sending some packets out of G0/0, and some packets out of G0/1. Sometimes load-balancing is a good thing, but in this case the G0/0 interface is totally wrong, so we should remove that configuration statement. DO SHOW RUNNING-CONFIG, PIPE, INCLUDE IP ROUTE. Okay, right click to copy, right click to paste. Hit CTRL-A to skip to the beginning of the line, and type no. Let’s see if the route was removed from the routing table. DO SHOW IP ROUTE. Okay, now we only have one route to 192.168.3.0/24, using the correct interface, G0/1. Finally let’s look for the issue on R3. First enter privileged exec mode with ENABLE. And once again I’ll check the interface configuration first. SHOW IP INTERFACE BRIEF. Both interfaces are UP/UP, however there is a misconfiguration here. R3’s gigabitethernet0/0 interface should have an IP address of 192.168.13.3, not 192.168.23.3. Let’s fix that. CONFIGURE TERMINAL. INTERFACE G0/0. Now, unlike when configuring routes, we don’t have to remove the current configuration first. If we enter a new IP address, it will overwrite the current IP address. Let’s see the config before and after. DO SHOW RUNNING-CONFIG. Okay, here’s the incorrect IP address. Now let’s configure the correct IP address. IP ADDRESS 192.168.13.3 255.255.255.0. Let’s check the config again. DO SHOW RUNNING-CONFIG. As you can see, the previous configuration was automatically overwritten, we did not have to delete it. Okay, since we are told there is one misconfiguration per router, we don’t have to check the routing table, but let’s take a quick look anyway. R3 should have a static route to the 192.168.1.0/24 network. DO SHOW IP ROUTE. There it is, via 192.168.13.2, which is R2. Now that we have fixed the misconfigurations, let’s go back on PC1 and try out that ping again. The first ping or two might fail, but after that they should all succeed. Let’s give it a shot. PING 192.168.3.1. Okay, so after finding and fixing the misconfigurations on R1, R2, and R3, PC1 is now able to ping PC2. That’s all for this lab. Thank you for watching. Please subscribe to the channel, like the video, leave a comment, and share the video with anyone else studying for the CCNA. If you want to leave a tip, check the links in the description. 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