Network Services Continued: DHCP and IPAM

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8 hours 20 minutes
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our next network service will take a look at is D H C P Dynamic Host Configuration protocol.
This allows the client to come on to the network, send out a Kerry and receive an I P address automatically
without D H C P. We would have to go to each system and statically configure an i p address.
This automates. That process makes life much easier.
You can see on the screen shot from Windows, where we've got the D. H. C P utility.
One of the most important things we have to think about doing is setting up a scope.
A scope is a range of IP addresses the D H C P server can issue.
So I might have a scope between 10 11 110 11 200 for instance, and then D H C P would be able to issue I P addresses anywhere in that range.
When I say D H C P will issue those addresses, it doesn't give a client I p addresses forever. Ain't nothing free.
What D H C P does is at least as an i p address to the client and the typical lease is eight days. So it released an address to a client for eight days. And if that client wants to renew their lease, they can contact the HCP after four days and ask, Hey, can I continue my lease? And if the HCP is accessible, it says, Sure.
If not, the client will try again and again. And if it can't contact the D. H C P server, the entire process just starts over.
Let's talk about what that leasing processes in just a second.
You can also reserve I P addresses for specific servers.
When you reserve an I P address, let's say I have a file server and I'd like that file server to always have the same I p address. I can create a reservation for that file server, enter its Mac address, and that way, when that file server comes online to get an I P address from D H C P. Based on smack,
it will be given that specific reserved I p address.
I can also exclude I p addresses from the range.
So maybe I'm going to give out I P addresses from 10 11 100 to 10 11 200 but 10 11 50 is a print server that I want to sign manually.
I can just exclude from that range. And 10, 11 50 won't be given to any other device, and I'll have to manually configure the print server.
So with reservations, a specific I P address is given to a specific host with exclusions. The I P address is removed from the range, and that requires the administrator to manually assign that address.
Sometimes exclusions are better.
If you have really critical servers, it's best to just statically assign an I P address.
Some services require that you do,
but also if you have a really critical server and you think about what would happen if D H. C P is down and I couldn't access that critical server, that could really be a problem.
When you have those really important servers on the network, it's probably just better to go ahead and give them a static address and exclude the address from that range.
I mentioned the leasing process just a few minutes ago, so let's go ahead and look at this.
You can remember the D H C P lease process through Dora Discover offer request acknowledge
The way the discovery process works is when a client comes online. It sends out a broadcast message that basically says, Hey, is anybody out there? D H C P server
Every D H C P server that Here's the query responds and says, I'm a d h c p server and here's an I P address for you.
Now the client is going to request the first i p address that it received as an offer.
Then that D H C P server is going to come back and acknowledge the client has been offered an I P address, and it's going to remove the I P address from its scope.
So that's the door process.
there are a couple little things to note here.
First of all, to start the Discover messages, a broadcast.
There are some devices that don't allow broadcast to pass specifically routers.
We'll talk in a later chapter about what routers are and some of the peculiarities of them. But one of the things the router does is lock broadcast.
There are some broadcast that you don't want to go through your entire network.
You might want some broadcast limited to certain segments. So router does that for us.
But if I'm trying to get an I P address on the other side of a router that my broadcast is going to be blocked,
there are a couple of things we can do about this.
There's something called a deep CP relay agent, which is a kind of service you install on the router that will Ford those D H C P requests.
There are also certain routers referred to as RFC 15 42 compliant routers.
You can also hear them referred to as boot P routers.
These will also forward those discover messages from clients.
All right,
so the next service we look at is called I Pam I P. Address management.
So we may be in an environment that has multiple locations throughout the world.
We may have thousands and thousands of hosts
when you start to work with a very large organization becomes very challenging to keep up with all your network segments, the hippies, mattresses and any sort of naming resolution issues.
So there are a series of software tools that will assist you with determining what I P addresses are in use whether or not they're being fully utilized in any sort of issues that might have with your D H C P server scope.
You could also even use it with incident response because it's able to detect the I P addresses that are being used.
So that's going to bring us to the end of the services. We looked at DNS DNS. For name resolution and determining where services are.
We looked at D H C P for automatic I p address assignment, and then we looked at I Pam as a means of managing a more complex environment and keeping track of I p address scopes and names as well.
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