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Cisco Catalyst 9117AX Series Access Points
Configuring DHCP Option 43
You can use DHCP Option 43 to provide a list of controller IP addresses to the access points, enabling them to find and
join a controller.
The following is a DHCP Option 43 configuration example on a Windows 2003 Enterprise DHCP server for use with Cisco
Catalyst lightweight access points. For other DHCP server implementations, consult product documentation for
configuring DHCP Option 43. In Option 43, you should use the IP address of the controller management interface.
Note
DHCP Option 43 is limited to one access point type per DHCP pool. You must configure a separate DHCP
pool for each access point type.
The 9117AX series access point uses the type-length-value (TLV) format for DHCP Option 43. DHCP servers must be
programmed to return the option based on the access point DHCP Vendor Class Identifier (VCI) string (DHCP Option 43).
The VCI string for the 9117AX series access point is:
Cisco AP c9117AX
The format of the TLV block is listed below:
Type—0xf1 (decimal 241)
Length—Number of controller IP addresses * 4
Value—IP addresses of the WLC management interfaces listed sequentially in hex
To configure DHCP Option 43 in the embedded Cisco IOS DHCP server, follow these steps:
Step 1
Enter configuration mode at the Cisco IOS CLI.
Step 2
Create the DHCP pool, including the necessary parameters such as default router and name server. A DHCP
scope example is as follows:
ip dhcp pool
<pool name>
network
<IP Network> <Netmask>
default-router
<Default router>
dns-server
<DNS Server>
Where:
<pool name> is the name of the DHCP pool, such as AP9117AX
<IP Network> is the network IP address where the controller resides, such as 10.0.15.1
<Netmask> is the subnet mask, such as 255.255.255.0
<Default router> is the IP address of the default router, such as 10.0.0.1
<DNS Server> is the IP address of the DNS server, such as 10.0.10.2
Step 3
Add the option 43 line using the following syntax:
option 43 hex
<
hex string
>
The
hex string
is assembled by concatenating the TLV values shown below:
Type
+
Length
+
Value
For example, suppose that there are two controllers with management interface IP addresses, 10.126.126.2 and
10.127.127.2. The type is
f1(hex)
. The length is
2 * 4 = 8 = 08 (hex)
. The IP addresses translate to
0a7e7e02
and
0a7f7f02.
Assembling the string then yields
f1080a7e7e020a7f7f02
. The resulting Cisco IOS command added to the
DHCP scope is
option 43 hex f1080a7e7e020a7f7f02
.
