Dhcp Options Windows
Introduction
This document describes how to use DHCP Option 43 and provides sample configurations for DHCP Option 43 for lightweight Cisco Aironet access points (LAPs) for these DHCP servers:
DHCP is used to dynamically assign IP addresses to client machines. This tutorial is written to help you to install and configure DHCP on Windows Server 2016. Once you have followed this article, go ahead with creating scopes and start leasing out IP addresses (which I have documented in another article). When a DHCP client receives information from a DHCP server only basic information, like IP / subnet / gateway / dns /etc, is visible. In some situations clients also receive DHCP options to set specific settings or application configurations (for example with Microsoft Lync or RES Workspace Manager). Knowing what options are received by the.
Microsoft Windows 2008 Enterprise DHCP Server
Cisco IOS速 DHCP Server
Linux Internet Systems Consortium (ISC) DHCP Server
Cisco Network Registrar DHCP Server
Lucent QIP DHCP Server
When a Cisco Wireless Unified architecture is deployed, the LAPs can use a vendor-specific DHCP Option 43 to join specific Wireless LAN Controllers (WLCs) when the WLC is in a different subnet than the LAP. Refer to Wireless LAN Controller and Lightweight Access Point Basic Configuration Example and Lightweight AP (LAP) Registration to a Wireless LAN Controller (WLC) for information on how to configure an access point (AP) to join a WLC.
Prerequisites
Requirements
Cisco recommends that you have knowledge of these topics:
Basic knowledge on Cisco Unified Wireles Network (CUWN)
Basic knowledge of DHCP
Components Used
This document is not restricted to specific software and hardware versions.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
Background Information
Vendor Specific DHCP Options
RFC 2132 defines two DHCP Options that are relevant to vendor specific options. They are Option 60 and Option 43. DHCP Option 60 is the Vendor Class Identifier (VCI). The VCI is a text string that uniquely identifies a type of vendor device. This table lists the VCIs used by Cisco APs:
| Access Point | Vendor Class Identifier (VCI) |
| Cisco Aironet 1000 Series | Airespace.AP1200 |
| Cisco Aironet 1040 Series | Cisco AP c1040 |
| Cisco Aironet 1100 Series | Cisco AP c1100 |
| Cisco Aironet 1130 Series | Cisco AP c1130 |
| Cisco Aironet 1140 Series | Cisco AP c1140 |
| Cisco Aironet 1200 Series | Cisco AP c1200 |
| Cisco Aironet 1230 Series | Cisco AP c1200 |
| Cisco Aironet 1240 Series | Cisco AP c1240 |
| Cisco Aironet 1250 Series | Cisco AP c1250 |
| Cisco Aironet 1260 Series | Cisco AP c1260 |
| Cisco Aironet 1300 Series | Cisco AP c1310 |
| Cisco Aironet 1500 Series | Cisco AP c15001 Cisco AP.OAP15002 Cisco AP.LAP15053 Cisco AP.LAP15104 Airespace.AP12005 |
| Cisco Aironet 1520 Series | Cisco AP c1520 |
| Cisco Aironet 1530 Series | Cisco AP c1530 |
| Cisco Aironet 1550 Series | Cisco AP c1550 |
| Cisco 3201 Lightweight Access Point | Cisco Bridge/AP/WGB c3201 |
| Cisco 521 Wireless Express Access Point | Cisco AP c520 |
| AP801 (embedded in 86x/88x Series ISRs | Cisco AP801 |
| Cisco Aironet 3500 Series | Cisco AP c3500 |
| Cisco Aironet 3600 Series | Cisco AP c3600 |
| AP802 (embedded in 88x Series ISRs | Cisco AP802 |
| Cisco Aironet 2700 Series | Cisco AP c27006 |
| Cisco Aironet 3700 Series | Cisco AP c37007 |
| Cisco Aironet 700 Series | Cisco AP c7006 |
| Cisco Aironet 1600 Series | Cisco AP c1600 |
| Cisco Aironet 1700 Series | Cisco AP c1700 |
| Cisco Aironet 1800s Series | Cisco AP c1800 |
| Cisco Aironet 1810 Series (incl OEAP) | Cisco AP c1810 |
| Cisco Aironet 1815 Series (I,W,T) | Cisco AP c18159 |
| Cisco Aironet 1830 Series | Cisco AP c1830 |
| Cisco Aironet 1850 Series | Cisco AP c1850 |
Cisco Industrial Wireless 3700 Series | Cisco AP iw3702 |
Cisco Aironet 1570 series | Cisco AP c1570 |
| Cisco Aironet 3800 series | Cisco AP c3800 |
| Cisco Aironet 2800 series | Cisco AP c2800 |
| Cisco Aironet 4800 series | Cisco AP c4800 |
| Cisco Aironet 1560 Series | Cisco AP c1560 |
| Cisco Aironet 1540 Series8 | Cisco AP c1540 |
| Cisco Catalyst 9115 Series | Cisco AP C9115AX |
| Cisco Catalyst 9117 Series | Cisco AP C9117AX |
| Cisco Catalyst 9120 Series | Cisco AP C9120AX |
1Any 1500 Series AP that runs 4.1 software
21500 OAP AP that runs 4.0 software
31505 Model AP that runs 4.0 software
41510 Model AP that runs 4.0 software
5Any 1500 Series AP that runs 3.2 software
6Any 2700/700/1530 Series AP that runs 7.6.120.0 or later software
7Any 3700 Series AP that runs 7.6 or later software
81540s running pre-FCS manufacturing code may use 'Cisco AP c1560'
91815s running pre-FCS manufacturing code may use 'Cisco AP c1810'
Also, see the the Cisco Wireless Solutions Software Compatibility Matrix.
Option 60 is included in the initial DHCP discover message that a DHCP client broadcasts in search of an IP address. Option 60 is used by DHCP clients (LAPs in this case) in order to identify itself to the DHCP server.
If the access point is ordered with the Service Provider option (AIR-OPT60-DHCP selected), the VCI string for that access point is different than those listed previously. The VCI string includes the ServiceProvider option. For example, a 1260 with this option returns this VCI string: Cisco AP c1260-ServiceProvider.
If the Cisco AP runs 7.0.116.0 or above (12.4 (23c) JA2 or above) and if a bootloader environmental variable (env_vars) named DHCP_OPTION_60 exists in flash, the value is appended to the VCI. If you order a Cisco AP with the Service Provider option, it will (by default) include the -ServiceProvider suffix; however, you can include other values into DHCP_OPTION_60 as well.
In order to facilitate AP discovery of WLAN controllers that use DHCP Option 43, the DHCP server must be programmed in order to return one or more WLAN controller management interface IP addresses based on the VCI of the AP. In order to do this, program the DHCP server to recognize the VCI for each access point type, and then define the vendor specific information.
On the DHCP server, the vendor specific information is mapped to VCI text strings. When the DHCP server sees a recognizable VCI in a DHCP discover from a DHCP client, it returns the mapped vendor specific information in its DHCP offer to the client as DHCP Option 43. On the DHCP server , option 43 is defined in each DHCP pool (Scope) that offers IP address to the LAPs.
RFC 2132 defines that DHCP servers must return vendor specific information as DHCP Option 43. The RFC allows vendors to define encapsulated vendor-specific sub-option codes between 0 and 255. The sub-options are all included in the DHCP offer as type-length-value (TLV) blocks embedded within Option 43. The definition of the sub-option codes and their related message format is left to the vendors.
When DHCP servers are programmed to offer WLAN Controller IP addresses as Option 43 for Cisco 1000 Series APs the sub-option TLV block is defined in this way:
Type - 0x66 (decimal 102).
Length: - A count of the characters of the ASCII string in the Value field. Length must include the commas if there is more than one controller specified, but not a zero-terminator.
Value: - A non-zero terminated ASCII string that is a comma-separated list of controllers. No spaces should be embedded in the list.
When DHCP servers are programmed to offer WLAN Controller IP addresses as Option 43 for other Cisco Aironet LAPs, the sub-option TLV block is defined in this way:
Type - 0xf1 (decimal 241).
Length - Number of controller IP addresses * 4.
Value - List of the WLC management interfaces, typically translated to hexadecimal values.
The semantics of DHCP server configuration vary based on the DHCP server vendor. This document contains specific instructions on the Microsoft DHCP server, Cisco IOS DHCP server, Linux ISC DHCP Server, Cisco Network Registrar DHCP server, and Lucent QIP DHCP Server. For other DHCP server products, consult the vendor documentation for instructions on vendor specific options.
Configure
Note: Use the Command Lookup Tool (registered customers only) in order to obtain more information on the commands used in this section.
Microsoft DHCP Server
This section describes the configurations necessary on the Microsoft DHCP server in order to use DHCP Option 43 for WLAN Controller discovery.
Cisco 1000 Series APs
This section describes how a Windows 2008 DHCP server is configured in order to return vendor specific information to Cisco 1000 APs. You need to know this key information:
Vendor Class Identifier (VCI)
Option 43 sub-option code
Management IP address(es) of WLAN controller(s)
The VCI for a Cisco 1000 Series AP is always Airespace.AP1200. As stated, the Option 43 sub-option code for the Cisco 1000 Series APs is type 102 (0x66).
Create a new vendor class in order to program the DHCP server to recognize the VCI Airespace.AP1200. In the Server Manager window, right-click the IPv4 icon, and choose Define Vendor Classes.
Click Add in order to create the new class.
Enter a value for the Display Name. In this example, Airespace is used as the Display Name. Also, add a short description of the vendor class in the Description field. Add the Vendor Class Identifier string. In order to do this, click the ASCII field and type in the appropriate value; in this case Airespace.AP1200. Click OK.
The new class is created. Click Close.
Add an entry for the WLAN controller sub-option in the Predefined Options for the newly created Vendor Class. This is where you define the sub-option code type and the data format that is used to deliver the vendor specific information to the APs. In order to create a Predefined Option, right click the IPv4 icon and choose Set Predefined Options.
A new window opens. Set the Option class to the value you configured for the vendor class. In this example, it is Airespace. Click OK in order to define the option code.
The Option Type box appears. In the Name field, enter a descriptive string value, for example, Airespace IP provision. Choose Binary as the Data Type. In the Code field, enter the sub-option value 102. Enter a Description, if desired. Click OK.
The new Predefined Option appears. Click OK. This completes the creation of the Vendor class and sub-option type needed in order to support controller discovery.
Right-click the Server Options folder under the DHCP scope, and choose Configure Options.
The Scope Options box appears. Click the Advanced tab. Choose the Vendor Class that you plan to use, in this case Airespace.
Choose the predefined 102 sub-option to assign to this scope. In the Data Entry area, enter the controller management IP address(es) to return to the APs in the ASCII section. This is a comma delimited list. There is a period (.) in the initial empty Data Entry area. Make sure you remove this period from the list of IP addresses added in the data entry area.
This is an example of the results.
Once you complete this step, the DHCP Option 43 is configured. This DHCP option is available for all the DHCP scopes that are configured in the DHCP server. So when the LAPs request for an IP address, the DHCP server sends the option 43 as well as to the LAPs.
Other Cisco Lightweight Access Points
The method described in the previous section can be used if you have multiple device types on the same scope and you want them to receive different WLC IP addresses via Option 43. But, if all of the DHCP clients in the scope are Cisco IOS APs, you can use this procedure to define DHCP Option 43.
Before you begin, you must know this information:
Option 43 sub-option code
Management IP address(es) of WLAN controller(s)
Complete these steps in order to define DHCP Option 43 on the Windows DHCP server:
In the DHCP Server scope, right-click Server Options and choose Configure Options.
On the General tab, scroll to Option 43 and check the 043 Vendor Specific Info check box.
Enter the Option 43 sub-option in hex.
Note: TLV values for the Option 43 suboption: Type + Length + Value. Type is always the suboption code 0xf1. 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, suppose there are two controllers with management interface IP addresses, 192.168.10.5 and 192.168.10.20. The type is 0xf1. The length is 2 * 4 = 8 = 0x08. The IP addresses translates to c0a80a05 (192.168.10.5) and c0a80a14 (192.168.10.20). When the string is assembled, it yields f108c0a80a05c0a80a14. The Cisco IOS command that is added to the DHCP scope is option 43 hex f108c0a80a05c0a80a14.
Click Apply and then click OK.
Once you complete this step, the DHCP Option 43 is configured and the DHCP server sends the option 43 to the LAPs.
Cisco IOS DHCP Server
Cisco Aironet APs (Cisco IOS)
Complete these steps in order to configure DHCP Option 43, in the embedded Cisco IOS DHCP server, for all Cisco Aironet APs that run Cisco IOS. This includes all APs except for the VxWorks 1000 Series (see the next section) and the 600 Series OEAP which does not use Option 43.
Enter configuration mode at the Cisco IOS CLI.
Create the DHCP pool, which includes the necessary parameters such as the default router and server name. This is an example DHCP scope:
Add the Option 43 line with this syntax:
The hexadecimal string in step 3 is assembled as a sequence of the TLV values for the Option 43 suboption: Type + Length + Value. Type is always the suboption code 0xf1. 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, suppose there are two controllers with management interface IP addresses, 192.168.10.5 and 192.168.10.20. The type is 0xf1. The length is 2 * 4 = 8 = 0x08. The IP addresses translate to c0a80a05 (192.168.10.5) and c0a80a14 (192.168.10.20). When the string is assembled, it yields f108c0a80a05c0a80a14. The Cisco IOS command that is added to the DHCP scope is:
Cisco Aironet 1000 Series APs (VxWorks) (1010/1020/1030/1505/1510) Series ONLY
Complete these steps in order to configure DHCP Option 43, in the embedded Cisco IOS DHCP server, for lightweight Cisco Aironet 1000 Series APs. This only applies to the 1010/1020/1030 model APs that run VxWorks, and not to APs that run IOS.
Enter configuration mode at the Cisco IOS CLI.
Create the DHCP pool, which includes the necessary parameters such as default router and server name. This is an example DHCP scope:
Add the Option 43 line with this syntax:
Note: The quotation marks must be included. A sub-option value does not need to be defined in the Cisco IOS DHCP server for Cisco 1000 Series APs.
For example, if you configure Option 43 for Cisco 1000 Series APs with the controller IP Management IP addresses 192.168.10.5 and 192.168.10.20, add this line to the DHCP pool in the Cisco IOS CLI:
Note: You must use the management interface of the WLAN controller.
Configure Dhcp Options
This video describes how to configure DHCP Option 43 on Cisco IOS DHCP Server: DHCP Option 43 on Cisco IOS DHCP Server .
Linux ISC DHCP Server
The information in this section describes how the Linux ISC server is configured in order to return vendor specific information to lightweight Cisco Aironet Series APs. This example configures the Linux ISC server to return vendor specific information to the 1140, 1200, 1130 and 1240 Series Lightweight APs. This configuration can be modified and applied to other series of LAPs.
Cisco Network Registrar DHCP Server
The Cisco Network Registrar DHCP server supports Vendor Specific attributes. However, the configuration of these attributes is not possible with the graphical interface. The CLI must be used.
Complete these configuration steps in order to support L3-LWAPP Discovery with DHCP Option 43:
Note: The CLI Command Tool can be found in the Network registrar directory: C:Program FilesNetwork RegistrarBIN nrcmd.bat
Dhcp Options Windows 7
- Log into the DHCP server. Complete these steps:
- Create the Vendor Class Identifier for Cisco AP1000 Series APs:
Create the Vendor Class Identifier for Cisco AP1200 Series APs:
Note: For other models of LAP, replace the vendor-class-id parameter with the specific VCI string from Table 1.
Associate the values that can be sent in the DHCP Offer by the server when it receives a request with Option 60 set to Airespace.AP1200. The DHCP Option 43 can support multiple values in the same Option 43 field. These options need to be identified individually by a subtype.
In this case, only one value is required, without any subtype. However, the Cisco Network Registrar (CNR) configuration requires that you create a subtype option.
Cisco AP1000 Series APs
Cisco AP1200 Series APs
However, in order to hide the subtype feature and send only a row string (BYTE_ARRAY) with the IP values, CNR supports specific flags in order to remove the subtype ids and length. These are no-suboption-opcode and no-suboption-len flags.
Cisco AP1000 Series APs
Cisco AP1200 Series APs
Associate values based on the DHCP pools:
Cisco AP1000 Series APs
Cisco AP1200 Series APs
In this example, the DHCP Pool named VLAN-52, which is already defined in CNR by the graphical interface, is configured with Option 43 10.150.1.15,10.150.50.15 when it receives a request from an Airespace.AP1200 device.
Note: 31:30:2e:31:35:30:2e:31:2e:31:35:2c:31:30:2e:31:35:30:2e:35:30:2e:31:35:2c is the hexadecimal representation of the string 10.150.1.15,10.150.50.15.
Finally, save the DHCP configuration and reload.
Refer to Managing Advanced DHCP Server Properties for more information on Vendor-Options configurations on a Cisco CNR DHCP server.
Lucent QIP DHCP Server
This section provides a few tips for how to configure the Lucent QIP DHCP server in order to return vendor specific information to lightweight Cisco Aironet Series APs.
Note:For complete information and the steps involved, refer to the documentation provided by the vendor.
The DHCP Option 43 can contain any vendor specific information. The DHCP server passes this information in the form of a hex string to the clients that receive the DHCP offer.
On the Lucent QIP DHCP server, the vendor-specific information can be provided on the DHCP Option Template- Modify page. In the Active Options area, choose Vendor Specific Information, and enter the information in the Value field.
In order to include the controller IP addresses in the DHCP option 43 message, enter the information to the DHCP Option template in QIP as a single hex value: [ip hex].
In order to send more than one IP address with DHCP Option 43, enter the information to the DHCP Option template in QIP as a single hex value:[ip hex ip hex] and not [ip hex],[ip hex]. In this case, the comma in the middle causes problems for DHCP to parse the string passed from QIP.
For example, suppose there are two controllers with management interface IP addresses, 192.168.10.5 and 192.168.10.20. The type is 0xf1. The length is 2 * 4 = 8 = 0x08. The IP addresses translate to c0a80a05 (192.168.10.5) and c0a80a14 (192.168.10.20). When the string is assembled, it yields f108c0a80a05c0a80a14. On the Lucent QIP DHCP server, the hex string that needs to be added to the DHCP scope is:
The hex string must be given within square brackets. The square brackets are mandatory. Once the DHCP option 43 is modified to reflect this value, the LAPs are able to find and register with the controller.
Verify
Use this section in order to verify your configuration.
The Output Interpreter Tool (registered customers only) supports certain show commands. Use the Output Interpreter Tool in order to view an analysis of show command output.
If you use 1130 /1200/1230/1240 Series LAPs, which have a console port, you can check that the WLC IP addresses are provided to the LAPs during DHCP IP address assignment. This is a sample output from a Cisco 1230 Series LAP:
If you use a Cisco IOS DHCP server, enter the show ip dhcp binding command in order to view the list of the DHCP addresses assigned to DHCP clients. Here is an example:
On the WLC CLI, you can enter the show ap summary command in order to verify that the APs registered with the WLC. Here is an example:
If you have Wireless LANs configured, you can enter the show client summary command in order to see the clients that are registered with the WLC:
Troubleshoot
Use this section in order to troubleshoot your configuration.
The Output Interpreter Tool (registered customers only) supports certain show commands. Use the Output Interpreter Tool in order to view an analysis of show command output.
Note: Refer to Important Information on Debug Commands before you use debug commands.
Enter the debug dhcp message enable command on the WLC in order to view the sequence of events that occur between the DHCP server and client. Here is an example:
Check Dhcp Options Windows
This is the debug lwapp packet enable command output from the WLC that indicates that DHCP option 43 is used as the discovery method in order to discover WLC IP addresses:
The value of the IE 58 parameter indicates the discovery type. For DCHP Option 43 it is 3.
Dhcp Options Windows 10
If you use the Cisco IOS DHCP server on the router, you can enter the debug dhcp detail command and the debug ip dhcp server events command in order to view the DHCP client and server activity. Here is an example from the debug ip dhcp server events command:
Enter the show ip dhcp binding command in order to view the list of the DHCP addresses assigned to DHCP clients.