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Cisco, Troubleshooting

Cisco’s Passive Client

Passive clients are wireless devices, such as printers, machine that are configured with a static IP address. These types of clients do not transmit any IP information when they associate with an AP. As a result, the WLC never knows the IP address of the client unless they use DHCP.

This feature is not supported by the AP groups and HREAP (Flex-Connect) centrally switched WLANs This feature works in multicast-multicast and multicast-unicast The controller sources the multicast packets using its management IP address. Earlier it was only supported on Cisco 5500 and Cisco 2100 Series Controllers but now 2504 WLC also supported.

WLCs 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.

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.

Passive client will allow unknown or broadcast ARPs to be sent across the wireless network, this feature is disabled by default.

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