Troubleshoot multicast

GA with allowlist: Access to Cloud Multicast is available to select Google Cloud customers. If you are interested, submit an access request form.

This page provides troubleshooting information for multicast.

For information about monitoring multicast traffic, see Observability for multicast.

Example commands for testing multicast traffic

This section provides example commands for testing multicast traffic by using the iperf tool. To run these example commands, you must set up the multicast configuration described Configuration overview.

Note: The example commands in this section use the iperf tool. If your VM instance doesn't have an external IP address, then you must configure Cloud NAT so that you can install the iperf package on the instance.

Send multicast traffic from a multicast producer

1. Connect to the instance by using SSH.

2. Install iperf if you haven't already.

   sudo apt install iperf
   

3. To send multicast traffic to the multicast group IP address, run the following command:

   iperf -c MULTICAST_GROUP_ADDRESS -p 1234 -l 1500 -i 1 -u -b 1000pps -t 999999
   

   Replace MULTICAST_GROUP_ADDRESS with the multicast group IP address.

Join a group and receive multicast traffic from a multicast consumer

1. Connect to the instance by using SSH.

2. Install iperf if you haven't already.

   sudo apt install iperf
   

3. To join a multicast group and log the traffic that you receive, run the following command:

   iperf -s -p 1234 -B MULTICAST_GROUP_ADDRESS -l 1500 -u -i 1
   

   Replace MULTICAST_GROUP_ADDRESS with the multicast group IP address.

   For example, the following command joins a group with the IP address 224.1.0.176 to receive packets up to 1500 bytes and logs the traffic received:

   iperf -s -p 1234 -B 224.1.0.176 -l 1500 -u -i 1
   

Troubleshoot specific issues

The following sections describe how to troubleshoot specific issues that you might encounter when using multicast.

Creating a multicast producer configuration fails

This section describes an error that might occur when attempting to create multicast producer and consumer configurations in the same VPC network.

If you complete the steps to enable a VPC network to consume multicast traffic before completing the corresponding steps to enable a VPC network to produce multicast traffic, then you receive an error similar to the following when attempting to complete the multicast producer configuration:

The request was invalid: MulticastProducerAssociation cannot be created in the
same network as MulticastConsumerAssociation. Please delete 
MulticastConsumerAssociation projects/PROJECT_ID/locations/ZONE/multicastConsumerAssociations/CONSUMER_ASSOCIATION_NAME
first.

To resolve this issue, do the following:

1. Delete the existing multicast consumer configurations. See Delete multicast consumer configurations.
2. Complete the multicast producer configuration. See Enable a VPC network to produce multicast traffic.
3. Complete the multicast consumer configuration. See Enable a VPC network to consume multicast traffic.

To prevent this issue from happening in the future, ensure that you complete the multicast producer configuration before the multicast consumer configuration if you plan to use the same VPC network to host both multicast producers and multicast consumers.

Multicast consumer can't receive multicast traffic

If your multicast consumer instance can't receive multicast traffic, do the following:

1. Ensure that firewall rules are configured to allow multicast traffic to the multicast consumer. For more information, see the following:
   • Multicast producer network firewall configuration
   • Multicast consumer network firewall configuration
2. Confirm the following:
   • The multicast group IP address is part of a range that has been activated by the multicast administrator
   • The multicast producer is sending traffic to the address
3. Ensure that you have completed the steps to enable IGMP query and force IGMPv2 on the multicast consumer instance. For more information, see Configure multicast consumer instances.

4. For multicast consumer VPC networks that are part of a multicast domain that uses the Network Connectivity Center (NCC) star topology, check the state of your multicast consumer configurations as described in View multicast consumer configurations.

   For a multicast consumer association, a state of INACTIVE indicates that you have lost access to the multicast domain. For a multicast group consumer activation, a state of INACTIVE indicates that you have lost access to the multicast group range. For more information, contact the multicast administrator.

Multicast producer or consumer experiencing packet loss

If a multicast producer or multicast consumer instance is experiencing packet loss, do the following:

1. Follow the instructions to Check network and OS statistics for packet discards due to resource exhaustion. The instance might be experiencing packet loss due to resource exhaustion, which can be caused by using a non-recommended machine type or using a machine type with insufficient vCPUs.

2. If necessary, update the instance to use a recommended machine type or to use a machine type with more vCPUs. For more information, see Machine considerations for multicast producers and consumers.

If you are still experiencing packet loss after updating your machine type, the multicast administrator might need to resize the multicast infrastructure for the domain as described in Update multicast domain parameters.

Join or leave taking a long time

During Google Cloud software rollouts, the infrastructure for a multicast domain may be temporarily unavailable to process new join and leave requests. IGMP membership reports are dropped and need to be re-sent.

To avoid disruptions caused by this issue, configure redundant multicast domains as part of a domain group to help ensure that the infrastructure for one domain remains available while the other domain is being upgraded. For more information, see Multicast domains.