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Updated:December 18, 2015

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Contents

Chromecast
Deployment Considerations
Chromecast Deployment using mDNS Gateway/ Feature Benefit
Components Used
Configuring mDNS Gateway for Chromecast on WLAN through GUI:
Configuring mDNS Profile through GUI
Accessing and Testing Chromecast
Chrome browser
Chromecast App on Android

Chromecast

Chromecast is a media streaming device from Google that plugs into an HDMI port on a high definition display. It lets us project from a client screen to a large screen (with a chromecast device) over a 2.4 MHz wireless connection. Users can cast audio/video content from their chrome browser (e.g. on a windows7 or a Mac laptop) or from chromecast app on an Android to a TV screen.

Two protocols are implemented on Chromecast to support discovery, the first is the DIAL Protocol over SSDP. This is the primary system used for the old version1 of Google Cast. The second protocol uses mDNS (multicast Domain Name System) protocol to search for available chromecasts on the wireless network. This is the primary way of discovering a Chromecast that supports the v2 API and is more popular. In this document, we will focus on mDNS device discovery for Chromecast. Devices using DIAL protocol for chromecast discovery are outside of the scope of the document.

Note

Chromecast works with a growing number of Apps. chromecast.com/apps. We have tested with chrome browser (with Chromecast extension installed) on Windows7 and MacBook Air clients and with Chromecast app on Android Samsung Galaxy S4, S6 Edge phones.

Deployment Considerations

mDNS protocol operates on service announcements and service queries which allow devices to ask and advertise specific applications such as:

Printing Services
File Sharing Services
Remote Desktop Services
iTunes File Sharing
iTunes Wireless iDevice Syncing (in Apple iOS v5.0+)
AirPlay offering the following streaming services:
- Music broadcasting in iOS v4.2+
- Video broadcasting in iOS v4.3+
- Full screen mirroring in iOS v5.0+ (iPad2, iPhone4S or later)

In addition to the above, we are adding Chromecast discovery using mDNS for the following specific applications:

Full screen mirroring on Chromecast extension enabled browser (Windows7, MacBook Air)
Mirroring of Android device using Chromecast App (Samsung Galaxy S4, Edge S6 phone)

Each query or advertisement is sent to the mDNS multicast address for delivery to all clients on the subnet. It relies on mDNS operating at UDP port 5353 and each query or advertisement is sent to the following reserved group addresses:

IPv4 Group Address – 224.0.0.251

The addresses used by the mDNS protocol are link-local multicast addresses and thus are only forwarded on the local L2 domain. Routers cannot use multicast routing to redirect the traffic because the time to live (TTL) is set to one, and link-local multicast is meant to stay local by design. This is not ideal for large networks that are segmented into vlans. Prior to this release, users would be required to configure end to end multicast to route multicast packets between vlans as explained in this document http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-6/chromecastDG76/ChromecastDG76.html#pgfId-23144

If you want to control mDNS, the key is to limit the size of the local segment.

To address this issue Cisco WLC acts as a Chromecast Gateway. The WLC listens for Chromecast services and by caching those Chromecast advertisements from the source/host e.g. Chromecast server, responds back to Chrome clients when a request for service is initiated. The following illustrates this process.

The controller listens for chromecast service/advertisements.
The WLC then caches those chromecast services.
Listens for the clients queries for chromecast service.
The WLC sends a unicast response to the client queries for chromecast service.

Chromecast Deployment using mDNS Gateway/ Feature Benefit

From 8.2 release, WLC supports mDNS gateway functionality for Chromecast for which the user does not need to enable multicast on the controller. The WLC will snoop all mDNS service advertisements and will not forward the same on AIR or Infra network. Clients can reside in the same or difference vlans as the chromecast service provider. mDNS AP is supported allowing controllers to have the visibility of wired chromecast service providers which are on VLANs that are not visible to the controller.

Components Used

Cisco 5520 Series Wireless LAN Controller
802.11n/ 802.11ac Access Points
Cisco Catalyst Switch
Chromecast device
Wireless clients (tablets, smartphones and so on.)

Configuring mDNS Gateway for Chromecast on WLAN through GUI:

To configure mDNS Gateway for Chromecast on WLAN through GUI, perform the following steps:

Procedure

Step 1

Create a dynamic interface for Chromecast services on separate VLAN than the Client VLAN to configure and demonstrate Chromecast feature on WLC.

Here is an example showing different interfaces and VLANs for Clients and Chromecast server:

Step 2

Create a WLAN for clients. By default mDNS Snooping is enabled on WLAN. To confirm, choose WLAN id > Advanced tab and make sure that the mDNS Snooping option is Enabled. Select the mDNS Profile as the default-mdns-profile to allow the mDNS services that you require to be advertised on a particular WLAN. Click Apply.

Wi-Fi Considerations

Chromecast devices do not support 802.1x, so Cisco recommends to create a separate SSID for Chromecast that supports WPA2 PSK (Pre-Shared Key).Chromecast devices have a single radio and work on the 2.4 GHz band. So, you need to make sure the SSID that the Chromecast devices are connected to is broadcasted on the 11b radio.

Note

Only one mDNS profile can be applied to one WLAN.

Step 3

Create another WLAN for services and make sure WLAN is mapped to an interface other than management as shown in the example.

Step 4

Connect the Chromecast device to the SSID created for device services and the chrome client (chrome browser on device or chromecast app on Android) to SSID for clients. Navigate to Monitor > Clients, the chromecast server and Client (tablet/laptop/phone) are associated to two different SSID's as shown.

From the example above, it is implied that the Chromecast server and the client are connected on different VLANs vlan_chromecast and vlan30 respectively.

Step 5

Click the client's MAC address of chromecast server as shown in the image above to view its details. Similarly, check to see if the server is associated to the interface mapped to a different VLAN than that of a client's. In this case it is on interface vlan_chromecast/ vlan 20.

Step 6

Now go back and click the MAC Address of client (MacBook/Windows7 or Android) to view its details. Check to see if the client is associated to the interface other than the services interface. In this case it is interface vlan30 on VLAN 30.

Configuring mDNS Profile through GUI

To configure mDNS profile through GU, perform the following steps:

Procedure

Step 1

To create and apply mDNS services, navigate to CONTROLLER > mDNS > General. To enable mDNS Global Snooping, check the mDNS Global Snooping check box under Global Configuration; as it is disabled by default and click Apply. Also, the Master Services Database shows the default profiles which are preconfigured.

The Master Service Database is a user configured database for all the mDNS services supported by WLC. As shown in the above figure, there is a default list of services like Apple TV and printer added to this list on start-up in the master service database. WLC snoops and learns about mDNS service advertisements only if the service is present in the master service list database. Similarly only those queries for services listed in the master-service-list will be responded back to clients subject to the condition that the mDNS profile name associated with the client allows for the service being queried for.

Step 2

To add mDNS services to the master-service-list database, from the Select Service drop-down list that display all services, choose the desired option. Each Service Name has a predefined service string.

Step 3

To add chromecast service, Select Service as “other”, choose a service name (example GoogleCast) and type service string as “_googlecast._tcp.local.” Hit the Add and Apply button after making the changes.

Note

In the case of a new install or install with clear config the GoogleCast string will be there by default.

Step 4

To select which services to be advertised click mDNS and then click Profiles. The default profile will appear. Navigate to Controller > mDNS > Profiles and select the default-mdns-profile.

Note

If the requirement is to use only default services then assign the default-mdns-profile to that particular WLAN on which you want to enable mDNS services.

Step 5

To check which mDNS services are running, click mDNS > Domain Names. In the example, you will notice Chromecast device is being discovered as a Wireless Medium.

Step 6

When mDNS Service shows up under Domain Name, verify to which mDNS profile it is tied to by navigating to mDNS > General > GoogleCast (in this example). As only the default profile is used, the services will show up under Profile Name, default-mdns-profile.

Accessing and Testing Chromecast

Chromecast Application

Clients with Chromecast extension installed on their Chrome browser can display the entire browser and screen by using a Chromecast device. Once the client discovers the Chromecast device using mDNS, the subsequent connections between the wireless client and Chromecast device to mirror the display use TCP based unicast messages.

Note

Chromecast works with a growing number of apps. chromecast.com/apps. We have tested with chrome browser (with Chromecast extension installed) on Windows7 and MacBook Air clients and with Chromecast app on Android Samsung Galaxy S4, and S6 Edge.

Configuration steps for client devices:

Chrome browser

Once the profile is attached to the WLAN as shown in previous procedure; proceed with testing to see if the Chromecast services are routed across the VLANs.

The screenshots are taken from a Windows7 client with chrome browser.

Chrome browser

The following screenshots are taken from a Windows7 client with chrome browser.

Procedure

Step 1	Install the GoogleCast Extension. Visit the store for chrome extension at:https://chrome.google.com/webstore/search-extensions/googlecast For more information on installing chrome extension visit: https://support.google.com/chrome/answer/167997?hl=en
Step 2	Notice the Googlecast tab at the top right corner of the chrome browser on installing the extension:
Step 3	Connect your client to the client SSID. Click the chromecast casting icon on the top right of chrome browser to discover Chromecast devices in your network. In the example below, device Lab_CCast was discovered by the client.
Step 4	Select the casting device (in this example, it is Lab_CCast) and it will begin casting your browser to the high definition monitor/TV screen with the chromecast device.

Chromecast App on Android

Once the mDNS profile is attached to the WLAN as shown in previous procedure, proceed with testing to see if the Chromecast service is routed across the VLANs.

The following screenshots are taken from Samsung Edge S6 phone.

Procedure

Step 1	Install Chromecast app on the phone.
Step 2	Make sure your Android is connected to the client SSID.
Step 3	Open the chromecast app to discover Chromecast devices in your network and to mirror your screen. In the example, the app found Lab_CCast chromecast device on the ssid.
Step 4	Connect to the chromecast device and start casting your screen to a high definition screen with the chromecast device.