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We've talked about network connections and how to manage them. We also need to look at troubleshooting them. Unfortunately network connections break or the network goes down or there's issues on the system that prevent connectivity to the network. There's several generic troubleshooting things you should look at before we get into some specific things. First of all, make sure your hardware is installed and working correctly. So if you just installed a new networking card and you can't connect to the network, well, maybe you need to look at the drivers and how it was installed. You may have to run sysinstall again and take a look at it. The next thing you want to check once you've established that the computer does pick it up and the drivers are correctly installed, is the configuration. You want to make sure that if you're statically configured, that you've typed in the correct IP address, gateway and subnet mask and so forth and if you're on DHCP, in other words you've got the DH Client Service running and that's enabling the network card to get this information automatically, make sure that's starting and running. And normally if you can pull an IP address down, you've normally got good network connectivity as far as your client goes. That's when you need to start exploring outside of the client, maybe look at the network cable. I know that's the obvious thing. That's usually one of the first thing that goes that causes a network outage is an unplugged cable somewhere. If that's not the problem, if you've got the driver installed, if you've got an IP address or it looks like things are working, then you may have to get in some more deeper things. Now, you probably will run some troubleshooting utilities to establish if you've got good connectivity, such as Ping, Trace Route, ARP and we've looked at some of these utilities earlier on in the previous session as a matter of fact so you've got those to help you establish connectivity and you've got those to help you establish if you've got consistent connectivity. Unfortunately one of the hardest problems to find is not necessarily whether you're connected or not because that's usually easy. You're either connected or you're not. The harder problem however is when we've got inconsistent connectivity, when it's intermittent or it keeps going down and come, go down, come up, go down. That's a hard one. That could still be a system problem but it also could be a network problem. Let's go ahead and take a look at some specific things you can do to help establish that you've got no connectivity and maybe fix some things on the box. One of the first things you should do when troubleshooting network connectivity issues in BSD UNIX or in any other brand of Linux or UNIX or whatever, is take a look at your drivers and your network card. Once you've done that, you might want to run the IF Config Command and just make sure that everything looks good. That you've got a valid IP address, that you're on the network you're supposed to and so forth and that you're showing these up. Now, one thing you can do if you suspect you've got a faulty configuration or a faulty card is take the interface down and up. And you can do that by typing If Config and make sure you get the right interface, LE0, down. That's disabling the interface and taking completely down and then bringing it back up and basically you just change Down to Up and come back up and it can take a couple of seconds for it to do that. That could clear out some intermittent problems but it may or may not solve the problem. So go back in and see if you're back up and active and you are and once you've done that, you need to start looking for other things. You need to start, for example, Pinging your default gateway. Right now our default gateway is probably one of the, 172.16.30.1. Let's try that and we get a reply back from that. So we know now from this that the connection between us and our default gateway is working. So likely if we're having network problems in this case, it would be beyond our own network. If you are not getting this reply back or if you're getting an intermittent reply back, in other words some of them returning and some of them not returning, then you may have a bad cable, you may have a loose connection or you could still have problems on the host itself. Sometimes intermittent problems are the hardest ones to track down. It could also be because you've got the wrong driver for the card installed or the card is not configured properly. Perhaps the network is configured for full duplex and you are not. So that could be an issue out there in network. Space could be an issue. It could be several different issues that you would need to look at and change and again, you can go into sysinstall and reconfigure the card if necessary. But troubleshooting networks is an art and a science. It's actually not that hard. The first thing is to establish where the problem is and where it's not. If you're a UNIX system administrator, you want to basically establish that the problem is not with the box, it's not with the card or the driver or the software. Then once you establish that the problem is in fact on the network, then you can get help with a network administrator and you can troubleshoot that problem down to what particular device or segment it's on. So that's just a little bit about network troubleshooting in general but specifically with BSD UNIX.