Google Cast

For screen sharing via Android, ChromeOS devices, Chrome web browsers.

Overview

Google Cast uses a combination of mDNS, SSDP, and TCP/UDP streams to discover and communicate with receiver devices. The following network requirements must be met for reliable mirroring from Android, ChromeOS, and Chrome browser clients.

Requirements

1

mDNS and SSDP discovery must be enabled

Google Cast discovery relies on two protocols:

mDNS

• UDP 5353

• Multicast address 224.0.0.251

• Bonjour service: _googlecast._tcp

SSDP

• UDP 190

• Multicast address 239.255.255.250

• ST/URN tags for Google Cast receivers

Requirements

• Multicast must be allowed on the WiFi network

• IGMP Snooping must not block SSDP or mDNS

• IGMP Querier required if snooping is enabled

• mDNS and SSDP must not be filtered, rate-limited, or converted to unicast in incompatible ways

• AP isolation must be disabled

If mDNS or SSDP is blocked, the sender will not see the Mago device in the Cast menu.

2

Google Cast across VLANs requires multicast forwarding

In single-VLAN networks Google Cast works without special configuration.

In multi-VLAN networks, Google Cast will not work unless multicast discovery is forwarded between VLANs.

You must enable one of the following (vendor-specific):

• mDNS gateway / Bonjour reflector

• SSDP multicast forwarding between VLANs

• Layer 3 multicast routing between specific VLANs

• Vendor “cast/airgroup multicast proxy” features (Cisco, Aruba, UniFi, Meraki, etc.)

If mDNS and SSDP packets do not cross VLAN boundaries, Google Cast will only work when clients and Mago are on the same VLAN.

3

Required Google Cast ports must be open

These are the ports used by Google Cast:

Port	Type	Direction	Service
8008-8019	TCP	Both	GoogleCast Listener Ports
1900	UDP	Both	SSDP Discovery
5353	UDP	Both	mDNS Discovery
32768-61000	TCP/UDP	Both	Ephemeral ports for client / server traffic

Requirements

• Both sender and Mago Room must be able to communicate over the ports above

• Firewall rules must allow inbound and outbound traffic

• NAT must not rewrite multicast packets (breaks SSDP/mDNS)

If ports 8008–8019 are blocked, Cast may appear but refuse to connect. If ephemeral ports are blocked, connection may start but fail mid-stream.

4

WiFi network configuration for Google Cast

Google Cast requires stable multicast behavior on the access point.

Check that:

• Multicast is enabled on the SSID

• Broadcast/multicast filtering is disabled or set to “unrestricted”

• Proxy ARP does not block or transform mDNS/SSDP packets

• DTIM settings are reasonable (DTIM 1–3 recommended)

• 5 GHz is available for high-bandwidth casting

• Client load on AP is not excessive

Chromecast and Android devices do not retry failed mDNS/SSDP packets aggressively, so multicast reliability is critical.

5

AP isolation must be disabled

Access point isolation (client isolation) prevents devices on the same SSID from communicating. Because Google Cast requires peer-to-peer communication:

• AP isolation must be disabled on the SSID used by client devices

• Wireless client privacy modes on the controller must be disabled

• Isolation in guest networks must be removed for the SSID used for casting

If isolation is enabled, devices may discover Mago (depending on broadcast bridging), but the connection will always fail.

6

Device and OS requirements

Google Cast requires compatible senders:

• Android 4.4+

• ChromeOS devices

• Chrome browser with Cast extension or built-in Cast support

• Some Windows/macOS apps support casting via Chrome browser

Receiver (Mago):

• Must be connected via Ethernet or a high-quality WiFi connection

• Must be reachable through firewall and VLAN configuration

7

Best practices for network reliability

To ensure smooth casting:

• Prefer Ethernet for the Mago device

• Use 5 GHz WiFi for sending devices

• Avoid DFS channels if Android devices have limited support

• Keep packet loss below 1 percent for stable video

• Minimize interference and channel congestion

• Ensure roaming between APs is not too aggressive

8

Bonjour service types required

Google Cast relies on mDNS to advertise available receivers. AirServer broadcasts the following Bonjour service types:

• _googlecast._tcp

• _display._tcp

• _airserver._tcp

These service types must be visible to the client device. If your network uses multiple VLANs, your mDNS gateway or Bonjour reflector must allow these service types to be forwarded.

If they are filtered or missing, clients may not discover the Mago Room device or may fail to connect during session negotiation.