Troubleshooting

Owned by alon.men@zixi.com
Last updated: 02 Sept 2020
2 min read

This section provides troubleshooting advise for some common multicasting-related issues.

Issue

Probable Cause

Solution
No multicast bitrate on Linux – The multicast stream is either 0 bitrate immediately, or its bitrate starts to drop to 0 after a while

Although typically this is an OS configuration or network configuration issue, it could be caused by the Zixi configuration.

  • In Zixi, make sure the correct local IP address is specified in the UDP input.
  • When using IGMPv3 - verify that correct SSM source IP is specified.
  • Leave the SSM field blank to allow accepting the multicast from any IP
  • Verify if the multicast is joined to the right group with ‘netstat -ng’
  • Monitor incoming traffic with tcpdump - see if it physically gets into the machine and then blocked in software, or if it doesn’t physically get there.
    • If it doesn’t get into the machine - this is a network issue.
    • If it gets to the machine but our application still shows 0 bitrate - it can be a routing/source IP issue.
  • Use 'socat' as a useful debug tool to verify if another program can get the data on the same machine.
    • If 'socat' can create a file - but our software can't see bitrate - this can be a bug. Contact R&D.
  • If the machine gets traffic in tcpdump, but not in software (ours or socat), then something is blocking it locally.
  • Verify that the source of the multicast is in the same subnet of the IP receiving it, or that there is a proper routing rule directing the multicast to the listening IP.
  • Verify the value of rp_filter (cat /proc/sys/net/ipv4/conf/eth0/rp_filter) - set it to 0 if needed (replace eth0 with the proper NIC, set it permanently in sysctl.conf).
  • Check that there is no firewall that blocks the multicast traffic.
  • Force IGMPv2 on the OS (rarely needed) -
    echo "2" > /proc/sys/net/ipv4/conf/eth0/force_igmp_version
    replace 'eth0' with the interface name. (Set it permanently with "net.ipv4.conf.default.force_igmp_version=2" in sysctl.conf)

Traffic on the UDP input on the Zixi Broadcaster side can looks doubled.

The same multicast address is available from multiple IPs (sometimes used for encoder redundancy)

  • Set rp_filter to 1 (if the multicast source is in the same subnet as the desired input IP).
  • Use the advanced "filter by SSM source IP" setting.