Multicast Between LAN and WLAN

[Cameron Prior]

Hi There

So I have just purchased an nVidia Shield for my media center needs and I've stumbled onto a bit of a problem.

The shield has chromecast built in - which is a fantastic idea - however the cast feature uses multicast and I've hit a snag.

My shield is connected to the LAN (vlan 20) and the device I am trying to cast from is connected to the WLAN (vlan 21). I am able to cast from devices connected to the LAN however devices on the WLAN cannot see the shield to cast to.

Now after doing a considerable amount of research and testing - I'm convinced its a multicast routing issue. 

I have followed the instructions in this document: https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-6/chromecastDG76/ChromecastDG76.html and have configured the WLC accordingly

I have also configured the core switch like this (239.1.10.10 is the multicast group address set on the WLC)

ip multicast-routing distributed
ip igmp snooping

interface Vlan20
 description Midgard.Local LAN Subnet
 ip address 10.0.20.1 255.255.255.0
 no ip redirects
 ip directed-broadcast
 no ip proxy-arp
 ip pim sparse-dense-mode
 ip igmp join-group 239.1.10.10
!
interface Vlan21
 description Midgard.Local WLAN Subnet
 ip address 10.0.21.1 255.255.255.0
 no ip redirects
 ip directed-broadcast
 no ip proxy-arp
 ip pim sparse-dense-mode
 ip igmp join-group 239.1.10.10

Im sure I have missed something simple here - but im not sure what it is.

Multicast is not my forte and ive not really ever had to troubleshoot it before.

Any help would be greatly appreciated.

[Cameron Prior]

So it turns out that chromcast uses mDNS (Bonjour Service) which does NOT like being routed - AT ALL!!

I ended up having to create a reflector to bounce the mDNS packets between the two subnets

https://chrisreinking.com/need-bonjour-across-vlans-set-up-an-avahi-gateway/

On this cisco side of things, I just created a trunk interface with a native vlan of 20 (My LAN Subnet)... Job done.

[Cameron Prior · Accepted solution]

So I have done some more reading about mDNS/Bonjour/Chromecast/Zeroconf and I have discovered that Cisco have indeed come up with a solution to our issue.

Cisco have included a new feature set in IOS 15.2 which allows you to extend mDNS services between subnets easily. The feature is called Service Discovery Gateway and it works a treat.

Basically you get the Layer 3 border to redistribute mDNS between any subnets you like.

Configuration is very simple (It can get pretty complicated if you want to filter specific traffic or types)

Global Configuration

service-list mdns-sd permit-all permit 10
!
service-routing mdns-sd
 service-policy permit-all IN
 service-policy permit-all OUT

Per Interface Config (Layer 3 Interface or SVI)

 service-routing mdns-sd
  service-policy permit-all IN
  service-policy permit-all OUT
  redistribute mdns-sd

Here is a really good slide deck I found about the whole thing.

https://www.slideshare.net/getyourbuildon/supporting-zeroconf-and-apple-bonjour-in-the-enterprise-using-ciscos-service-discovery-gateway-techadvantage-webinar

Hope this helps