Passive Client Feature

In this post we will learn about the passive client feature.

My Real Problem Scenario:

From last 2 weeks I am facing problem with a device connected behind a WGB. This device has static IP address.

I tried before 2 weeks and it was working but now it’s not. I don’t know what was wrong.

So on one hand it is working (At one place) – Did not enable passive client , still working

On other hand it’s not working (on another location) – Enable passive client and its working

So let’s deep drive in to this topic:

What is 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 unless they use the DHCP.

Must Remembering Points:

  • This feature is not supported with 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.

How to configure:

  • Enable multicast-multicast mode
  • Enable the global multicast mode
  • Enabling the Passive Client Feature

Via GUI:

Enable Multicast-Multicast mode:

Controller > General, Select AP multicast mode and put the Multicast Group IP address and then Apply.

Passive1

Enable the Global Multicast Mode:

Choose Controller > Multicast, select both the boxes and then Apply

Passive2

Enable the Passive Client Feature:

Choose WLANs > WLANs > WLAN ID to open the WLANs > Edit page

Go to Advanced tab, Select the Passive Client box and then Apply

Passive3

Via CLI:

Enable multicast-multicast mode:

(WLC1) >config network multicast ?
 global         Enter mode.
 igmp           Igmp paratemers set
 l2mcast        Configuration of L2 Multicast
 mode           Configure WLC to AP Multicast/Broadcast traffic forwarding mode.
(WLC1) >config network multicast mode ?
 multicast      Mcast/Bcast Packets are encapsulated in multicast CAPWAP tunnel to APs
(WLC1) >config network multicast mode multicast ?
 <IP addr>      Mcast/Bcast Packets are encapsulated in multicast CAPWAP tunnel to APs
(WLC1) >config network multicast mode multicast 239.239.35.1

Enable the global multicast mode:

(WLC1) >config network multicast global ?
 enable         Enables this setting.
 disable        Disables this setting.
(WLC1) >config network multicast global enable
(WLC1) >config network multicast igmp ?
 query          Igmp Query paratemers set
 snooping       Igmp snooping configuration
 timeout        Igmp timeout set
(WLC1) >config network multicast igmp snooping ?
 enable         Enable Igmp snooping
 disable        Disable Igmp snooping
(WLC1) >config network multicast igmp snooping enable

Enabling the Passive Client Feature:

(WLC1) >config wlan passive-client enable ?
 <WLAN id>      Enter WLAN Identifier between 1 and 16.
(WLC1) >config wlan disable 8
(WLC1) >config wlan passive-client ?
 disable        Disable passive-client feature on a WLAN.
 enable         Enable passive-client feature on a WLAN.
(WLC1) >config wlan passive-client enable 8

Verification:

(WLC1) >show wlan 8
 .
 WLAN Identifier.................................. 8
 Profile Name..................................... Test
 Network Name (SSID).............................. test
 .
 .
 .
 IPv6 Support..................................... Disabled
 Passive Client Feature........................... Enabled
 Peer-to-Peer Blocking Action..................... Disabled
(WLC1) >

That’s all, now my Passive device is working 🙂

Unicast, Broadcast and Multicast

Earlier I was so confused with these terms..may be many of others have same problems like me or may be not.

Here I tried to explain in simple way(Also copied many things from internet to make it simple and easy to understand. )

Unicast

Unicast packets are sent from host to host. The communication is from a single host to another single host. There is one device transmitting a message destined for one receiver. In another words, Unicast transmission is between one-to-one nodes (involving two nodes only).

Examples of Unicast transmission are http, smtp, telnet, ssh, pop3 where the request for information is directed from one sender to only one receiver at the other end.

To understand this better, try to imagine a scenario where one computer’s request for the URL(google.com) is received by every other computer that’s connected to the Internet. This way Internet will be flooded with such requests and therefore there is a strong need for Unicast transmission on small and large networks. All Ethernet and IP networks support this type of transmission.

Unicast uses TCP for its communication and packet transmission.

Broadcast

Broadcast is when a single device is transmitting a message to all other devices in a given address range. This broadcast could reach all hosts on the subnet, all subnets, or all hosts on all subnets. Broadcast packets have the host (and/or subnet) portion of the address set to all ones. By design, most modern routers will block IP broadcast traffic and restrict it to the local subnet.

In other words, broadcast is a type of transmission in which information is sent from just one computer but is received by all the computers connected to the network. This would mean that every time a computer or a node would transmit a packet of type ‘broadcast’, all the other computers will receive that information packet.

Examples of broadcast are many but one that would be best to understand here is a computer booting up and requesting for a IP address. In this case, the computer which is booting up and requesting for an IP address does not know which computer will be able to provide it with an IP address. It will then broadcast a request packet on the network which will be received by all the other computers but will be acknowledged by only the computer acting as a DHCP server. One other example would be that of the ARP (Address Resolution Protocol) which will broadcast the address resolution request to all other computers on the network.

Broadcast uses TCP for its communication and packet transmission.

Multicast

Multicast is a very much different from Unicast and Multicast in definition and application as well. It is a type of transmission or communication in which there may be more than one senders and the information sent is meant for a set of receivers. Please note that sometimes information might not be directed towards any receiver at all.

Multicast is a special protocol for use with IP. Multicast enables a single device to communicate with a specific set of hosts, not defined by any standard IP address and mask combination. This allows for communication that resembles a conference call. Anyone from anywhere can join the conference, and everyone at the conference hears what the speaker has to say. The speaker’s message isn’t broadcasted everywhere, but only to those in the conference call itself. A special set of addresses is used for multicast communication.

Multicast operates on a different class of IP address (Class D IP Series). All the other computers electing to receive information in a multicasted network must be a part of Multicast IP based network. Also, unlike Unicast and Broadcast which uses TCP for its communication, Multicast uses UDP. This is only because TCP does not support Multicast mode of communication.

Example of Multicast based network is video transmission network in which one computer needs to transmit video channel to a specific group of computers. This way when the other computers are also a part of this Multicast IP network, they will be able to receive same set of data at the same time. Multicast offers savings on bandwidth and is the preferred way of data communication when data is to transmitted to a set of computers.