The CompTIA A+ exams have many network troubleshooting scenario questions. Mike gives you a few rules to help you get through these questions. In addition, a few basic tools and preparation makes troubleshooting most problems easy if not trivial.
- Okay folks, it's your buddy the great Mike Stramy here yet again to talk about troubleshooting issues. Now I'm going to do it a little bit differently this time because we've already discovered so much troubleshooting in networking that all I want to do is wrap it up with a couple little zen concepts that I want to make sure you understand. Look, the A plus is going to be filled, and I mean filled, with big long hairy looking networking questions that are really pretty simple as long as you stick to a couple of basic rules. Number 1: Understand how networks work. And Number 2: Go with a couple of rules that always work for me. Number 1: Don't let the physical get you down. If you think there's a problem with your physical network, always check that first. Check your link lights, take a look at the lower right hand corner on a Windows system or upper right hand corner on a Linux or a Mac system and verify that you have actual connectivity before you start blaming anything else. Now once that's out of the way there's some other things we can do. Number 1: Ye shall know your network. In particular, it's absolutely imperative that you know your network ID, that you know what your router is, and that you know what your DNS server is. It's so easy to do, just run ipconfig. - [Mike] In fact, let's run it with the slash all. When you run this, you automatically get all the information you want. Here's your IPv6 address, here's your IPv4 address, here's your default gateway, both in IPv6 and IPv4. If you have a DHCP server it's going to tell you where that is right here. If you've got a DNS server and you do, it will show you right here. - You should know this. You should know this before there's a problem. I don't care if you're at home, or at your office, or in a big huge enterprise, if you're in charge of IT, you make sure you just know these things and you document it. Take little pieces of paper and draw circles with network IDs in 'em and stuff so that when trouble comes along, you'll know what to do with it. The other tool you need to know is that you need to know your internet connectivity. So most servers have some router some place, but in a lot of situations we may have two or three internal routers before we get out to the actual internet itself. And anytime someone says the internet's down it would be nice to be able to check to see if you can get a connection. And that's where a very powerful program called Trace route comes into play. The power of Trace route is you run it when everything's good so you know what it's supposed to look like and then if something's bad, you can deal with it. Let's run Trace route. - [Mike] So it's spelled Trace route like this in Windows but it's traceroute spelled all the way out on Mac and Linux machines. So what we're going to do is we just want to go some place out on the internet. It doesn't matter where you go. I'm going to pick a web page in this particular example. So I'm going to let this guy run. So it's going out to a IPv6 address. Now take a look here. First of all, because we ran ipconfig slash all, we know that our internal network starts with a 2603. So this is my internal network and now this is combing out to probably my gateway router and then a bunch of other connections. - So the idea here, is you get to know all the routers to get out of the internet. So for me I've got one internal router, and then I've got one gateway router out to the internet. Let's do this again because you don't have to use a webpage. - [Mike] Just pick some arbitrary ftp site. Now this is an IPv4 one so let's watch. So there's my internal router that totalhome 192.168.4. There's that 96.120 is my gateway router out to the internet. And here's all bunch of this one's far away man, we got to go and go and go. So you'll see here on Trace route we're starting to see some asterisks. That's because some routers are designed not to respond back. But it's still okay. What it's showing us is that we're out of the internal networks and out to the internet. - Look if the internet goes down, and it's one of your routers, then it's your problem. So I could run traceroute again in the future, and let's say I only get one hop, just one, it never gets to my gateway router. That's telling me that there's probably something between my internal router and my gateway router that I need to deal with. Trace route is an incredibly powerful tool, just run it before you have any problems and know all of your internal routers. If something breaks down out there in the world of Comcast or something like that, you're not going to fix that but at least you're aware there's nothing wrong with the routers for you to get out to your ISP. Got the idea? The other one I want to talk about is Ping. Ping is one of these commands that does so much goodness for us in one shot it's not even funny. Like for example, - [Mike] I'm going to just run Ping real quick, and I'm going to ping my router because I know what my router is because I've looked with ipconfig slash all and I have it memorized. So I run this and I get a reply. I automatically know, automatically know, that I've got a good IP address on this system, and I know that the router is responding so it's probably up and running. Ping is an amazing tool when used properly. Here's another trick you can do with Ping, watch this. Now I'm going to run a ping here and I'm just picking some arbitrary ftp site in this case. Now look, it's timing out do you see that? - Who cares? What I want you to do let's look at this one more time, and I want you to recognize something very very important that's happening. - [Mike] I pinged a fully qualified domain name and it returned an IP address. Do you see that 134? - You want to know if your DNS server's working? Just try to ping something by it's fully qualified domain name. Ba! You don't have to use nslookup or any of that stuff. Just a quick ping by a fully qualified domain name is the best test of a DNS server you could possibly think of. Now I could only give you a few ideas in this episode about troubleshooting networks. Keep in mind, that there are lots of tools out there you could get for all kinds of things. But for me, 95% of the time, I fix all of my network problems with just Ping, Trace route, and ipconfig. Use those three tools you're going to see them all over the exam, practice with them, play with them, you're going to love 'em. (mood music)