Set up auto-discovery & multicast routing between VLANs ⎌

The Airtame device uses Multicast to advertise itself on a network so that the app can detect it, showing a list of all Airtame devices on the network. The methods used are Simple Service Discovery Protocol (SSDP) and Multicast Domain Name Service (mDNS).

The App will send a multicast join request to join the multicast group 239.255.255.250 over port UDP 1900-1901 or 224.0.0.251 over port UDP 5353 to discover the available devices. See the article Network Integration & Setup to see which ports are used for different Airtame features to work on your network.  Below are what the packet transactions for both SSDP and mDNS should look like.

You can control what discovery protocol to use by selecting one in the Airtame app (v3.5.0 and up):

What if you have multiple VLANs?

Simply enabling the Multicast protocol on one VLAN will work if Airtames and PCs are on the same VLAN but in the case that Airtames and PCs are on different VLANs, the multicast traffic will need to cross VLANs. Therefore, some additional multicast routing configurations on the Network side are needed from the network administrator.

• To use multicast across various VLANs, you will need to use PIM.

PIM (Protocol Independent Multicast) is a routing protocol for Multicast Traffic. As you enable Multicast with “ ip multicast-routing” in global configuration mode, the router will be enabled for multicast. IGP (Interior Gateway Protocol) routing protocols exchange network information of one router’s network with others. The same multicast Protocol will exchange multicast information of Routers with each other. 

Instructions on how to do this vary depending on the brand of network you are using. For example Cisco equipment.

• Now you need to choose between Sparse or Dense mode.

1. Dense Mode is much easier since you just need to write a simple command to set up PIM on the VLAN. Using Dense mode, the source tree will start from the source network that is generating multicast traffic and other Multicast host Routers will be acting like branches of the tree that are trying to access the multicast stream. In PIM dense mode the router will initially flood multicast packets across the network. This process will help in creating (S, G) entry in all routers. This process is repeated every three minutes in PIM dense mode.  In this process, those routers which don’t need the multicast stream can be pruned back from the traffic flow.

2. Sparse Mode is more complicated since you need to set up a rendezvous point. PIM sparse mode has a central point of contact for all Multicast host routers. As the routers receive the request from the host to join a particular multicast group, they will check the multicast routing table which is received from PIM. And in case that the router is not aware, the request will be forwarded to the RP (Rendezvous Point). RP is a designated router in the network selected by the network administrator as per requirement/Topology. This router will be responsible for providing information about every multicast group to host. All multicast sources will register with the RP which, in turn, will be aware of all multicast groups and how to reach the multicast sources.

In the end, it is the network admin's responsibility to choose the model that fits the organization and to follow the guidelines for PIM setup specific to the brand of network used. Here's more information about setup on Cisco Equipment. If you would like to download a PDF of the following deployment guide, click here for Airtame 1 and here for Airtame 2