Multicast Issue in Layer 2: VLC Not Receiving Stream

[Thonno]

Hello everyone,

I am encountering issues with setting up multicast traffic in a Layer 2 environment. Although the PCs can ping each other and are correctly connected to the Wi-Fi network, the VLC client is unable to receive the multicast stream sent by OBS Studio.

Scenario

The network Lab consists of the following devices:

• 1 FortiGate
• 2 FortiSwitch
• 2 FortiAP
• 2 PCs on Wi-Fi (IPs: 172.16.0.2 and 172.16.0.3), one running OBS Studio and the other running VLC.

Topology

• FortiGate
  • Port 1 connected to Port 24 on FortiSwitch 1.
  • Port 2 connected to Port 24 on FortiSwitch 2.
• FortiSwitch 1 and 2
  • Connected to each other through Port 23.
  • FortiAP connected to Port 21 on each FortiSwitch.

Configuration

1. VLAN 200 for Wi-Fi Network:

   • Subnet: 172.16.0.0/22
   • FortiGate Gateway: 172.16.0.1
   • DHCP managed by FortiGate: Range 172.16.0.100 - 172.16.0.254

2. IGMP Snooping Enabled on FortiSwitches and FortiAP:

   • IGMP snooping is enabled globally on both FortiSwitches and FortiAP.
   • IGMP Querier is disabled since multicast traffic is expected to remain within Layer 2.
   • I have enabled IGMP on FSW1 and FSW2 port 21, 23 and 24 with the following commands:

config switch-controller managed-switch

edit <FortiSwitch_serial_number>

config ports

edit <port_name>

set igmp-snooping-flood-reports {enable | disable}

set mcast-snooping-flood-traffic {enable | disable}

end

end

1. OBS Studio Configuration:

   • OBS Studio is streaming on multicast IP 239.0.0.1 on port 1234 using UDP.

2. VLC Configuration:

   • VLC client attempts to open the stream with the following address:
     perl

     udp://@239.0.0.1:1234

The Issue

Although the network seems properly configured, VLC is unable to receive the multicast stream from OBS Studio. The two PCs connected to the Wi-Fi network (172.16.0.2 for VLC and 172.16.0.3 for OBS) can ping each other, so there is no basic connectivity issue. Both Windows firewalls are disabled.

Here are the troubleshooting steps I have tried, but without success

1. I temporarily disabled IGMP snooping, but the issue persists.
2. Multicast forwarding is enabled on the FortiGate, although no Layer 3 routing is required since this is a Layer 2 scenario.
3. I tested a unicast stream from OBS Studio to VLC, and the stream works correctly, confirming that the issue is specific to multicast.

Request for Help

It seems like everything is configured properly, but multicast traffic is not being distributed correctly by the FortiSwitch or FortiAP. Has anyone experienced a similar setup or have suggestions on what to check or adjust to make multicast work in Layer 2 with VLC?

Thanks in advance for your support!

Some indications:

1. The two FortiSwitches have been connected, and the FortiGate automatically configured them. (Do we need to configure any trunks for this?)
2. I also tried enabling the multicast router and the policies, but it still doesn't work.

3. The SSIDs are configured in bridge mode, and I have enabled IGMP on both the SSID interfaces and the VLAN 200 interface.

4. The two APs are connected in native VLAN 100 (Management) and allowed VLAN 200 (Wi-Fi).

I might be making mistakes in enabling multicast and IGMP. I've tried following different guides from Fortinet, but they all say different things, so I'm getting confused.

[akileshc]

Hello Thonno,

Based on your explanation, it seems no further changes to VLAN or trunk configurations are required, as unicast connectivity between the receiver and sender is functioning correctly.

Since your setup only involves a multicast sender and receiver, there is no need for multicast routing. However, ensure that multicast-forwarding is enabled and that the multicast policy between the relevant interfaces is correctly configured. If the issue persists, capturing sniffer logs using the following command may assist with further troubleshooting:

`di sniffer packet any "host xx.xx.xx.xx" 4 0 l`
(Replace xx.xx.xx.xx with the multicast group IP address.)

[Thonno]

Hi, I resolved the issue. The problem was caused by the PC running OBS, which had some unknown issues. After changing the PC, the multicast streaming in Layer 2 is now working.

I modified the infrastructure so that the PC with OBS is on a different VLAN than the users connected via Wi-Fi.

Here are the steps I followed:

BASIC CONFIGURATION:

• Create a multicast router on:

  • Wi-Fi users VLAN
  • Wi-Fi regia VLAN

• Enable multicast forwarding:

  config system settings

  set multicast-forward enable

  end

• Enable multicast on SSIDs (multicast-to-unicast):

  config wireless-controller vap

  edit "SSID_NAME"

  set multicast-enhance enable

  next

  end

TUNING:

• Enable IGMP snooping on:

  • Wi-Fi users VLAN
  • Wi-Fi regia VLAN

• Create a static group:

  config router multicast-flow

  edit static-group

  config flows

  edit 1

  set group-addr 239.0.0.1

  set source-addr 10.10.16.2 #PC Regia IP

  next

  end

  next

  end

• Assign static group to multicast routers (both WIFI_USERS and WIFI_REGIA):

  config router multicast

  config interface

  edit WIFI_REGIA

  set multicast-flow static-group

  set static-group static-group

  next

  edit WIFI_USERS

  set multicast-flow static-group

  set static-group static-group

  end

• Set FortiGate as Querier (on both WIFI_USERS and WIFI_REGIA):

  config system interface

  edit WIFI_USERS

  set switch-controller-igmp-snooping enable

  set switch-controller-igmp-snooping-proxy enable

  set switch-controller-igmp-snooping-fast-leave enable

  next

  edit WIFI_REGIA

  set switch-controller-igmp-snooping enable

  set switch-controller-igmp-snooping-proxy enable

  set switch-controller-igmp-snooping-fast-leave enable

  next

  end

• Disable unknown multicast flooding:

  config switch-controller igmp-snooping

  set flood-unknown-multicast disable

  end

Do you think there are any other adjustments I should make to improve the flow and avoid network congestion? The infrastructure is designed to support more than 1,000 users connected simultaneously to 12 APs (with 12 different SSIDs, all in bridge mode).

The goal is to ensure that the firewall acts as a querier without overloading the network.

[akileshc · Accepted solution]

Hello Thonno,

If the FortiGate configuration includes multicast PIM-SM with a static group entry, multicast forwarding must be disabled. This is because the FortiGate can support either forwarding or routing per VDOM at any given time, not both simultaneously.