operates on service announcements and service queries which allow devices to
ask and advertise specific applications such as:
In addition to the
above, we are adding Chromecast discovery using mDNS for the following specific
mirroring on Chromecast extension enabled browser (Windows7, MacBook Air)
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:
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
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.
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.