Configuring Passive Clients

Restrictions for Passive Clients

  • The interface associated to the WLAN must have a VLAN tagging.

  • GARP forwarding must to be enabled using the show advanced hotspot command.


    Note
    Client ARP forwarding will not work if any one of the two scenarios, mentioned above, is not configured.

  • The passive client feature is not supported with the AP groups and FlexConnect centrally switched WLANs.

Passive Clients

Passive clients are wireless devices, such as scales and printers that are configured with a static IP address. These clients do not transmit any IP information such as IP address, subnet mask, and gateway information when they associate with an access point. As a result, when passive clients are used, the controller never knows the IP address unless they use the DHCP.

Wireless LAN controllers currently act as a proxy for ARP requests. Upon receiving an ARP request, the controller responds with an ARP response instead of passing the request directly to the client. This scenario has two advantages:

  • The upstream device that sends out the ARP request to the client will not know where the client is located.

  • Power for battery-operated devices such as mobile phones and printers is preserved because they do not have to respond to every ARP requests.

Since the wireless controller does not have any IP related information about passive clients, it cannot respond to any ARP requests. The current behavior does not allow the transfer of ARP requests to passive clients. Any application that tries to access a passive client will fail.

The passive client feature enables the ARP requests and responses to be exchanged between wired and wireless clients. This feature when enabled, allows the controller to pass ARP requests from wired to wireless clients until the desired wireless client gets to the RUN state.


Note
For FlexConnect APs with locally switched WLANs, passive client feature enables the broadcast of ARP requests and the APs respond on behalf of the client.

This section contains the following subsections:

Configuring Passive Clients (GUI)

Before you begin

To configure passive clients, you must enable multicast-multicast or multicast-unicast mode.

Procedure

Step 1

Choose Controller > General to open the General page.

Step 2

From the AP Multicast Mode drop-down list, choose Multicast. The Multicast Group Address text box is displayed.

Step 3

In the Multicast Group Address text box, enter the IP address of the multicast group.

Step 4

Click Apply.

Step 5

Enable global multicast mode as follows:

  1. Choose Controller > Multicast.

  2. Check the Enable Global Multicast Mode check box.

Enabling the Multicast-Multicast Mode (GUI)

Before you begin

To configure passive clients, you must enable multicast-multicast or multicast-unicast mode.

Procedure

Step 1

Choose Controller > General to open the General page.

Step 2

Choose one of the following options from the AP Multicast Mode drop-down list:

  • Unicast—Configures the controller to use the unicast method to send multicast packets. This is the default value.

  • Multicast—Configures the controller to use the multicast method to send multicast packets to a CAPWAP multicast group.

Step 3

From the AP Multicast Mode drop-down list, choose Multicast. The Multicast Group Address text box is displayed.

Note 

It is not possible to configure the AP multicast mode for Cisco Flex 7510 WLCs because only unicast is supported.
Step 4

In the Multicast Group Address text box, enter the IP address of the multicast group.

Step 5

Click Apply.

Step 6

Enable global multicast mode as follows:

  1. Choose Controller > Multicast.

  2. Check the Enable Global Multicast Mode check box.

Enabling the Global Multicast Mode on Controllers (GUI)

Procedure

Step 1

Choose Controller > Multicast to open the Multicast page.

Note 

The Enable IGMP Snooping text box is highlighted only when you enable the Enable Global Multicast mode. The IGMP Timeout (seconds) text box is highlighted only when you enable the Enable IGMP Snooping text box.

Step 2

Select the Enable Global Multicast Mode check box to enable the multicast mode. This step configures the controller to use the multicast method to send multicast packets to a CAPWAP multicast group.

Note 

It is not possible to configure Global Multicast Mode for Cisco Flex 7510 WLCs.
Step 3

Select the Enable IGMP Snooping check box to enable the IGMP snooping. The default value is disabled.

Step 4

In the IGMP Timeout text box to set the IGMP timeout, enter a value between 30 and 7200 seconds.
Step 5

Click Apply to commit your changes.

Enabling the Passive Client Feature on the Controller (GUI)

Procedure

Step 1

Choose WLANs > WLANs > WLAN ID to open the WLANs > Edit page. By default, the General tab is displayed.

Step 2

Choose the Advanced tab.

Step 3

Select the Passive Client check box to enable the passive client feature.

Step 4

Click Apply to commit your changes.

Configuring Passive Clients (CLI)

Procedure

Step 1

Enable multicasting on the controller by entering this command:

config network multicast global enable

The default value is disabled.

Step 2

Configure the controller to use multicast to send multicast to an access point by entering this command:

config network multicast mode multicast multicast_group_IP_address

Step 3

Configure passive client on a wireless LAN by entering this command:

config wlan passive-client {enable | disable} wlan_id

Step 4

Configure a WLAN by entering this command:

config wlan

Step 5

Save your changes by entering this command:

save config

Step 6

Display the passive client information on a particular WLAN by entering this command:

show wlan 2

Step 7

Verify if the passive client is associated correctly with the AP and if the passive client has moved into the DHCP required state at the controller by entering this command:

debug client mac_address

Step 8

Display the detailed information for a client by entering this command:

show client detail mac_address

Step 9

Check if the client moves into the run state, when a wired client tries to contact the client by entering this command:

debug client mac_address

Step 10

Configure and check if the ARP request is forwarded from the wired side to the wireless side by entering this command:

debug arp all enable

Note 

Cisco WLC detects duplicate IP addresses based on the ARP table, and not based on the VLAN information. If two clients in different VLANs are using the same IP address, Cisco WLC reports IP conflict and sends GARP. This is not limited to two wired clients, but also for a wired client and a wireless client.