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DEMO: Configuring DHCP

A wireless LAN controller can serve as its own DHCP server, eliminating the need to rely on a Layer 3 switch for IP address assignment on wireless networks. This content covers how to configure a DHCP scope directly on the WLC and bind it to a specific wireless interface.

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About this video

A wireless LAN controller includes a built-in DHCP server capability, allowing it to assign IP addresses to wireless clients independently of any upstream Layer 3 switch. While a Layer 3 switch is a common choice for DHCP services across VLANs, there are scenarios where bypassing it entirely is preferable. A guest VLAN is a clear example, since isolating that traffic from the core switching infrastructure improves both security and administrative simplicity. Shifting DHCP responsibility to the WLC keeps guest network management self-contained within the wireless environment. Configuring the internal DHCP server requires creating a named scope under the controller's internal DHCP settings, then defining the address pool range, network address, default gateway, DNS server, and lease duration. Once the scope is enabled, it must be associated with the appropriate network interface by setting the primary DHCP server field on that interface to the controller's own management IP address, effectively pointing the interface at itself. After applying the change, wireless clients connecting to the associated SSID receive addresses drawn from the configured pool, confirming the controller is handling DHCP assignment end to end.

What you'll learn

What's covered

WLC as DHCP Server

Aligned to

Cisco CCNA
2.9 Interpret the wireless LAN GUI configuration for client connectivity
4.3 Explain the role of DHCP and DNS within the network
4.6 Configure and verify DHCP client and relay
2.6 Describe Cisco Wireless Architectures and AP modes

Key terms

Dynamic Host Configuration Protocol
DHCP
A network protocol that automatically assigns IP addresses and other configuration parameters to devices on a network.
IP Address
A numerical label assigned to each device connected to a network that uses the Internet Protocol.
Virtual LAN
VLAN
A logical grouping of network devices that behave as if they are on the same network regardless of physical location.
Default Gateway
The router that a device uses to send traffic to destinations outside its local network.
Domain Name System
DNS
A hierarchical naming system that translates human-readable domain names into IP addresses.
Wireless LAN Controller
WLC
A network device that provides centralized management of multiple lightweight wireless access points, handling functions such as client authentication, roaming, radio frequency management, and security policy enforcement. WLCs communicate with APs using CAPWAP and allow network-wide wireless configuration from a single management point.
DHCP Scope
The defined pool of IP addresses that a DHCP server is configured to assign to clients on a specific subnet, along with associated options such as the subnet mask, default gateway, and DNS servers. Each subnet served by a DHCP server has its own scope.

Topics

Dhcp Wireless Lan Controller Networking Ip Addressing Wlan Network Configuration

Transcript

Why Run DHCP on the Controller

One thing that your wireless LAN controller can do is hand out IP addresses. Your wireless LAN controller can act as a DHCP server.

Up until now it's been our layer 3 switch that acted as the DHCP server, and what we can do is use that layer 3 switch to hand out IP addresses for our wireless LANs. That's what we did in the case of VLAN 30 -- my machine got an IP address from the layer 3 switch. But perhaps we want to cut that layer 3 switch out. An example of where we might use this is something like a guest VLAN. With a guest VLAN, I might not want to have touched that switch at all, and everything be handled through the wireless controller.

So we're going to learn how to set up a DHCP scope on our wireless LAN controller and then get our wireless LANs to be able to hand out IP addresses. In this demo we're going to set up a scope for our management VLAN.

Creating the Scope

First of all, I'm going to go to the Controller tab, and then within the Controller tab I see on the left-hand side here an Internal DHCP Server, so I'm going to open that up and click on DHCP Scope. Now I'm seeing all the scopes, which -- we haven't set anything up, so there's nothing here.

I'm going to select New here. I'm going to give it a scope name, and I'm going to just call this Management, because I'm going to create a scope for our management VLAN. I'll hit Apply, and there it is.

Now I'm going to select this to actually configure it. The starting pool for this network, let's do 10.1.10.224, and the ending will be 10.1.10.23. So I'm just going to hand out a few. One of the reasons why I might just hand out a few on this network is because I don't really want a lot of devices connecting to this management VLAN, so this is one way to limit that to a certain degree.

I'm going to give it the network. 10.1.10.0 is the network address. I can give it a time to live, and what I've got there is just fine. The default routers for this network, which is 10.1.10.1. The DNS domain name, so we'll call this andy.lan. The DNS server -- so far we've just been using 8.8.8.8 as our DNS server, so I'll do that the same here. A NetBIOS name server: I don't have a NetBIOS server on this at this time, so I'm going to leave that just the way it is. And then status -- we will go ahead and enable this, and then hit Apply. So now this scope is activated.

Applying the Scope to the Management Interface

Next what I need to do is apply this to the management network, and the way I do that is a little interesting. I'm going to go under Interfaces and then click on the management interface, and then within the management interface I have this primary DHCP server, where I specify the primary DHCP server.

Right now this is specifying 10.1.10.6, which doesn't really exist, so I'm going to change this to dot five, which is the management address of the wireless LAN controller. You can see that it's specified right there, so essentially it's referencing itself. I'm going to choose that, I'm going to then enable this, and I will hit Apply. Then it's going to warn me this could cause a disruption. I'm fine with that.

Testing It

Once I've done that, I can open this up and I can connect to the tks10 network -- that's my management network. So I'm going to do that and I will select Connect. If we've set this all up correctly, what it will do is it will get an IP in that DHCP scope.

I just do a refresh on this. Looks like it's connected. I'll bring up the command prompt and type in ipconfig, and I see the IPv4 is 10.1.10.224, which is the first address in that scope. So now it is handing out IP addresses to the machines that connect to this wireless LAN. We've set this up, and now we will be able to communicate to other devices on this network.

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