From the course: CompTIA Network+ (N10-009) Cert Prep

Network service scenarios

From the course: CompTIA Network+ (N10-009) Cert Prep

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Network service scenarios

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- Network services are the lifeblood of what makes our networks go. If it wasn't for servers offering different types of services, everything from file sharing to printers, to email to web servers, literally everything that makes us do all this would be meaningless. So in this episode, I want to go through some service issues that come into play. Now, keep in mind, in previous episodes, we've actually kind of covered a number of scenarios already. But in this particular episode, I want to really kind of build the scenario concept a little bit more and talk about some really common problems. And probably the biggest problem that we run into with networks more than anything else is going to be DHCP. Automatic IP addressing is a great concept, but we just run into issues all the time. So I just want to cover some potential issues. So let's say I've got a DHCP server right here, and I'm going to keep it simple. And this DHCP servers handing out to these three, there's probably 200 more other computers, but we'll just start out with these three guys. Now, certain problems really come into play. One big issue is the concept of reservations. Let's say this guy is a server, he's a file server. This is where we store all of our video files here at Total Seminars. So if I have a DHCP scope that say is going to be 192.168.4.2 to 192.168.4.254, we're already running into a problem. The big thing you got to remember with the DHCP scope is that if you put up a range like that, it's going to pass 'em all out as long as it can. Now, certain things come into play. For example, we know that our default gateway is 192.168.4.1. So we would never, ever put our gateway in the scope or otherwise that DHCP server is going to start passing out 192.168.4.1 and suddenly nobody can get on the internet, get the idea? So this is one example of an IP reservation. However, this file server is a busy guy and he is always going to be out there and he's always going to be working. So one of the things that's very common for us to do is to reserve an address for him. So one of the things I like to do is my DHCP scope will start at around 100. My goal for doing this is simple. What I'm trying to do is keep one through 99 open for things like file servers, wireless access points, printers, things like that, that don't want to move and shouldn't change their IP addresses. Now keep in mind, and we do cover this in other episodes, if I want to, I can exclude from this range and I've seen this done where people will go from one to 254 and then create a huge number of exclusions. They'll make IP exclusions that say, don't go into this one. I think that's a bad idea. Reduce your DHCP scope as much as possible and then make your IP reservations that way. Another trick you can do is that if you have a system where it's not critical that it has a specific IP address, but it should always have an IP address. We can do what's known as a MAC reservation in this case, file server would probably be a bad idea, but say a camera. Here, let me throw a camera in here. In this case, we don't care that the camera, what the IP address is 'cause I'm using some kind of DNS to get the camera name, but I want that camera to be working all the time, even if we run out of addresses. So what I can do with this guy is I can give him a MAC reservation and this is all set up in the DHCP server. So what I'm doing with the MAC reservations, I'm going to get his MAC address and I'm going to go up to the DHCP server and I say, anytime you see this MAC address, even if you have to knock somebody else out, you make sure he has one. All DHCP servers have this feature. So this brings up the real scenario situation, and I promise you, you're going to be seeing something like this. John has a system that he wants to get on and, I'm sorry, he wants to log in and do his morning's work, but he can't get on. So the first thing he does, 'cause he's a good user, is he checks his IP address and he sees he gets a 1.69.254 dot something dot something. What should John consider as a problem? Now they're going to give you some extra stuff. First of all, it's an APIPA, which we automatically know means he's not getting an IP address from the DHCP server. Those things happen, but I'm going to make it more interesting to you. The file server continues to get an IP address. Some camera will always get an IP address, starting to see what's about to happen here. And other systems on the network sometimes will, and the word sometimes is what you got to watch out for in these scenarios. Sometimes will and sometimes won't get an IP address. They're just going in, they're doing their IP config release, then they do an IP config renew. And sometimes it works and sometimes it doesn't. And what's happening here more than anything else is that you have exhausted this scope. You've just plain old run out of addresses. So what do we do about this? Well, in most situations, especially where you have desktop machines, you run out of this because you just haven't set enough aside and you just add more to it, you know? So you'll usually see, especially scenarios on the exam, they'll only have like 10 addresses in the scope. Just add more. But there's another thing I want you to consider. If you come into a world, and I know that we haven't officially covered wireless in order, but I'm going to bring this into play, is that, let me grab one of my laptops here. The big mistake that people make with DHCP scopes is they set really long leases. Windows, for example, by default, has an eight day lease. So if you got big desktops that never move, that's great, go for it. That's why Microsoft put it there. What if you got a coffee shop? You got a coffee shop? I don't know, did anybody out there drink coffee? How long do you sit around in the coffee shop? Oh, I got one buddy. One of my editors will sit there for six hours. They don't like him very much, but generally people kind of move in and out of coffee shops within say an hour. If you're setting your DHCP scope to eight hours or just leaving it to default, you didn't even bother changing your lease time from the default of eight days. What's going to happen here? Well, the bottom line is, unless these people with laptops are really nice and actually log off and how many people do that with their phones? They just walk in, find a wireless network, do their YouTube or whatever, and then they just walk away with their cafe mocho frappuccino or whatever the things are called. They don't actually let go of their lease. And as a result of that, you get very quickly exhausted DHCP scopes. And this is a huge, huge problem. Anybody who's running any type of public wireless service knows that one of the first things you do on your DHCP server is you drop that lease time down to, I see people do one hour, and it works out pretty good. So watch out for scenarios like that because they can be a huge issue when you're trying to deal with lots and lots of people drinking lots and lots of coffee. The bottom line is, is that DHCP servers by themselves are not the end all perfect tool that we used to like them to be. We've reached a point, especially now where we not only have IPV four, but IPV six, which we cover in other episodes, that the process of keeping track of all of our IP addresses just becomes onerous and simply going into a DHCP server and reacting to these types of problems doesn't make sense anymore. So what we do instead these days, especially when you have virtualized systems, is we turn to an entire class of systems known as IPAM and that is IP address management. IPAM tools are designed to do one thing, keep track of all of your IP addresses no matter where they're happening, no matter what they're doing, and take care of the needs of addressing for your system. IPAM tools are very, very powerful. They can automatically create new DHCP scopes. They can reservations, they can generate new blocks of addresses as long as it's within a range of addresses you have control on, and can keep your systems running up no matter what happens. You don't see IPAM too terribly much in terms of individual desktops, but for servers, huge farms of virtual machines, IPAM is certainly the way we take care of these types of addressing scenarios going forward.

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