December 19, 2022

1. 4_1- Basic Troubleshooting Commands

In this section, we are going to talk about basic shooting commands, and we are starting with filtering the Show IP route output. If you want to filter the Show IP route, you can use the Show IP route, and for example, if you want to check just a specific IP address or network ID, you can type that IP address and show the IP route routing about this specific IP address, or you can use the longer prefixes keyword as well. The Show IP route longer prefixes option allows you to see any subnets of the network you specified if they are present in the routing table. Assume you are an ISP (Internet service provider) and you have assigned an IP block to your customer. You are unaware of how your customer further submitted this IP block and are unconcerned about it. However, for some reason, you do not need to check if there are any subnets from this IP block in your routing table.

So the command will be “Show IP Route,” and the “Show IP Route 16” command will finish with the longer prefixes. This command will then display all of the network’s known subnets. In your routing table, you learned sixteen, zero, zero, slash 15. And the other filtering method is to use include, exclude, and begin keywords. To use these keywords, you are typing, for example, the Show command. In this example, we’re using Show Press CPU, then a pipe, and if you type Include, and if you type the keyword, the iOS displays only the lines with the IP input. And if we just use exclude while typing a keyword, the iOS is excluding the lines that occur without an assigned keyword this time.

And we can also use the beginning keyword if you use the “Show running configuration” option. Begin line VTY, for example. This time, iOS displays the lines starting with the lime v. Skyworth. We can also check a specific portion of the Show run output. For this, we are using the section keyword. For example, if we just want to check the IPSL configuration, we can use the Show Ram Pipe Section Ipsli command. If we want to check the BGP configuration or OSPF configuration, we can use “Show Ram Pipe Section” for BGP or OSPF or something like that. This section also includes the Redirect T and Append options. The redirect option does not display the output on the console, but what this option is doing is, for example, typing “Show Tech Support.”

We have a Show Tech Support output in here, and this output is being redirected directly to a txtp server with the name “shorted TXT.” This is the file, okay, but you don’t see anything on your screen. As you can see, we can also use option two. Show an IP interface, a brief pipe, a flash show, and a brief take t, for example. The T option displays the output on the console and sends it to the file. All right, what T is doing is we are seeing the output in here, show IP interface, brief output, and it is also being sent to the Flash with the name of show and brief TXT. All right, when you use the Dear Flash, we can use the Show and Brief TXT in here, and as you can see, we also have an append option. This append option allows you to add command output to an existing file. That’s the only difference. All right, and we have the pink. Pink is the most basic command, as you can see. You send the ICMP echos to the remote site, and you receive the ICMP replies to verify the communication between two devices. Okay, if you use the repeat keyword with the pink, you send more pink packets.

By default, the Cisco iOS pink command sends out five ICMP eco request packets, and the repeat option enables you to specify how many eco request packets are sent. And in here we have another option while using Ping, and we are pinging an iPad in here, as you can see. And we are using a size keyword, and the DFP size keyword option enables you to specify the total size of the pink packet, including headers in bytes that will be sent in combination with the repeat option. You can send a steady stream of large packets and generate some load. And we have DFP, as you can see; this option set includes the “don’t fragment” bit in the IP header to indicate that routers should not fragment this packet. If it is larger than the NTU of the outbound interface, the router should drop the packet and send an ICMP fragmentation needed and Dfbitset message back to the source. This option can prove very useful when you are troubleshooting MTU-related problems. We also have a source option lens. As you can see, this option enables you to set the source IP address of the interface of the pink packet. In addition, we have expanded the PowerPoint, which you can see here. In extended ping, we are typing the justping keyword and hitting enter.

Then iOS starts asking us questions. target IP address, repeat count, datagram size, timeout of 18 seconds, extended comments, yes or no, source address or interfacetype of source, and blah, blah, blah. As you can see, you can fill out all of them or leave some of them blank, and you can use the extended pink as a good troubleshooting tool. All right, when we execute a pink command, we get to reply with some symbols. For example, here we have this symbol that means a successful answer return. Life is good when we see this guy; life is bad when we see this guy’s. If we see serial points, we know that life is bad and that the answer is a failed answer. That is, if we see you, it means your destination is inaccessible. Perhaps an access list is preventing access after reaching the device.

If we see Q, the resource is Plc, m means the package failed to fragment, a question mark means the package type is unknown, and an ampersand means the package time has expired. And if we want to get real-time information about the devices, we can use debugging options as enough. For example, if we type “debug Iposp Adjacency” or “debug Iposp events,” we see the real-time OSPF packets shared from the devices with each other, so we can define hardware problems in the iOS and troubleshoot them with some commands as well. The first command is, as you can see, “Show memory.” Maybe you can see your memory status by using “Show memory,” or we can use “Show press CPU sorted” to see the processes that are consuming our CPU on our device. For example, in this case, we have CPU utilisation of 4% for 5 seconds and see something like 1%, 6% for 1 minute, and 5% for 5 minutes. This guy’s four, six, and five in the output show the total CPU value used in the packet switch in the last 5 seconds. 1 minute, 5 minutes, and this guy is indicating the CPU values spent on the interruption in the packet switch.

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