How to configure DHCP Option 43 for Cisco Lightweight Access Points

In this post I covered the DHCP Option 43 configuration steps for Cisco Aironet lightweight access points. The DHCP Option 43 is for add a Wireless LAN Controller IP address in DHCP server, after that Cisco Aironet lightweight access points will get a both IP address details and WLC IP address from DHCP server. This includes the DHCP Option 43 configuration for 1000, 1100, 1130, 1200, 1240 and 1300 series Cisco Aironet Access Points.

We can configure the IP DHCP Server on Cisco Router or L3 Switch, we can add the DHCP Option 43 configuration in Cisco IOS DHCP server for use with Cisco Aironet lightweight access points. You can also configure DHCP Option 43 on Microsoft, Sun Solaris, Linux, and Lucent QIP DHCP servers.

In DHCP Option 43, you should use the IP address of the WLAN controller management interface. 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.  Cisco Aironet 1000 and 1500 series access points use a comma-separated string format for DHCP Option 43. Other Cisco Aironet lightweight access points use the type-length-value (TLV) format for DHCP Option 43. DHCP servers must be programmed to return the option based on the access point’s DHCP Vendor Class Identifier (VCI) string (DHCP Option 60). The VCI strings for Cisco access points capable of operating in lightweight mode are listed below.

Cisco 1130 and 1140 Lightweight access points

Cisco 1130 and 1140 Lightweight Access Points

 

 

 

 

 

 

 

Lightweight Access Point VCI Strings for 1000 and 1500 Series Cisco LWAPs

Lightweight Access Point        Vendor Class Identifier (VCI)

Cisco Aironet 1000 series             Airespace.AP1200
Cisco Aironet 1100 series             Cisco AP c1100
Cisco Aironet 1130 series             Cisco AP c1130
Cisco Aironet 1200 series             Cisco AP c1200
Cisco Aironet 1240 series             Cisco AP c1240
Cisco Aironet 1300 series             Cisco AP c1300
Cisco Aironet 1500 series             Cisco AP.LAP1510?

TLV Format for 1100,1130,1200,1240,1250 and 1300 Series Cisco LWAPs 

The format of the TLV block for 1100, 1130, 1200, 1240, 1250, and 1300 series lightweight access points is listed below:

• Type: 0xf1 (decimal 241)
• Length: Number of controller IP addresses * 4
• Value: List of WLC IP address management interfaces

Configure DHCP Option 43 for 1000 Series Cisco Lightweight Access Points

To configure DHCP Option 43 for Cisco 1000 series lightweight access points with Cisco IOS DHCP server in Router or L3 Switch follows below steps:

Step 1 Enter configuration mode at the Cisco IOS command line interface (CLI).

Cisco#configure terminal
Cisco(config)#

Step 2 Create the DHCP pool, including the necessary parameters such as default router and DNS servers. A DHCP scope example is as follows:

Cisco(config)#ip dhcp pool <pool name>
Cisco(dhcp-config)network <IP Network> <Netmask>
Cisco(dhcp-config)default-router <Default router>
Cisco(dhcp-config)dns-server <DNS Server>

Where:

<pool name> is the name of the DHCP pool, such as AP1000
<IP Network> is the network IP address where the controller resides, such as 10.10.0.1
<Netmask> is the subnet mask, such as 255.255.255.0
<Default router> is the IP address of the default router, such as 10.10.0.1
<DNS Server> is the IP address of the DNS server, such as 10.10.10.2

Step 3 Add the DHCP option 60 line using the following syntax:

Cisco(dhcp-config)#option 60 ascii “Airespace.AP1200”

The quotation marks must be included.

Step 4 Add the DHCP option 43 line using the following syntax:

 Cisco(dhcp-config)option 43 ascii “Comma Separated IP Address List

 For example, if you are configuring DHCP option 43 for Cisco 1000 series access points using the controller IP addresses 10.126.126.2 and 10.127.127.2, add the following line to the DHCP pool in the Cisco IOS CLI:

Cisco(dhcp-config)option 43 ascii “10.126.126.2,10.127.127.2”

The quotation marks must be included.

Configure DHCP Option 43 for 1100, 1130, 1200, 1240, and 1300 Series Cisco Lightweight Access Points

To configure DHCP Option 43 for Cisco Aironet 1100, 1130, 1200, 1240, and 1300 series lightweight access points in the embedded Cisco IOS DHCP server, follow below steps:

Step 1 Enter configuration mode at the Cisco IOS CLI.

Cisco#configure terminal
Cisco(config)#

Step 2 Create the DHCP pool, including the necessary parameters such as default router and name server. A DHCP scope example is as follows:

Cisco(config)#ip dhcp pool <pool name>
Cisco(dhcp-config)#network <IP Network> <Netmask>
Cisco(dhcp-config)#default-router <Default router>
Cisco(dhcp-config)#dns-server <DNS Server>

Where:

<pool name> is the name of the DHCP pool, such as AP1240
<IP Network> is the network IP address where the controller resides, such as 10.10.0.0
<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 10.10.10.2

Step 3 Add the DHCP option 60 line using the following syntax:

Cisco(dhcp-config)#option 60 ascii “VCI string

For the VCI string, use the value from above table. The quotation marks must be included.

Step 4 Add the DHCP option 43 line using the following syntax:

Cisco(dhcp-config)#option 43 hex <hex string>

The hex string is assembled by concatenating the TLV values shown below:

Type + Length + Value

Type is always f1(hex). Length is the number of controller management IP addresses times 4 in hex. Value is the IP address of the controller listed sequentially in hex.

For example 1, suppose that there is one controllers with management interface IP addresses, 10.126.126.2. The type is f1(hex). The length is 1* 4 = 4 = 04 (hex). The IP addresses translate to 0a7e7e02. Assembling the string then yields f1040a7e7e02. The resulting Cisco IOS command added to the DHCP scope is listed below:

 Cisco(dhcp-config)#option 43 hex f1040a7e7e02
Or
 Cisco(dhcp-config)#option 43 hex f104.0a7e.7e02

For example 2, 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 listed below:

Cisco(dhcp-config)#option 43 hex f1080a7e7e020a7f7f02

 

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  1. Nani says:

    I understand both DHCP option 43 and 60 configuration. Thanks alot.

  2. Raj says:

    Very nice info on DHCP option 43 configuration on Cisco Router or L3 Switch for Cisco Lightweight Access points.

    Thanks…

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