Troubleshooting UDP reception

UDP (User Datagram Protocol) - communication protocol in local networks or Internet, with minimal delays and minimal stability.

Software to analyze your issue

Analyze UDP with Astra MPEG-TS Analyzer

With Astra you can analyze any supported source. Just launch in console next command:

astra --analyze "udp://[email protected]:1234"

To stop Astra analyzer press Ctrl+C. Read more about Astra MPEG-TS Analyzer

Analyze UDP with Tcpdump

Tcpdump is a common tool to check network traffic. For example, command to check UDP multicast receiving to group on the interface eth0:

tcpdump -pnni eth0 udp and host

If you don't know actual interface you may find it with command:

ip route get

The tcpdump output looks like many lines with information about packets source, destination, and length. For example:

21:38:42.143839 IP > UDP, length 1316
21:38:42.143868 IP > UDP, length 1316

To stop tcpdump press Ctrl+C

UDP Not working at all

Not working means a zero bitrate in the Astra MPEG-TS Analyzer output. For example:

Jan 27 09:00:00: INFO: Bitrate: 0 Kbit/s
Jan 27 09:00:01: INFO: Bitrate: 0 Kbit/s

No UDP packets on interface

First of all check traffic on the network interface with tcpdump tool. If there is no information about incoming packets, then need to check network configuration or source configuration.

  1. Invalid routes configuration. If you have has several interfaces, please, check that route to multicast group configured correctly or define interface name in the udp address
  2. Connectivity issues. Check that you server connected to ethernet or vlan interface created
  3. Incompatable IGMP Version. For example your server uses IGMPv3, but network equipment supports only IGMPv2: Configure IGMP Version

Software unable to receive UDP packets

If tcpdump shows information about UDP packets, there is could be next issues:

  1. UDP droped by firewall rulles. Check your firewall configuration
  2. If you server has multiplay interfaces then append route to the multicast group or configure RP Filter: RP Filter and Multicast receiving in Linux

Too many errors on receiving UDP

CC (Continuity Counter) errors indicates that packets continuity is corrupted. Error can be caused by packets loss or excess. Example output with CC errors in the Astra MPEG-TS Analyzer:

Jan 27 09:00:00: INFO: Bitrate: 13259 Kbit/s
Jan 27 09:00:00: ERROR: CC: PID:18=3 PID:20=3 PID:256=24
Jan 27 09:00:01: INFO: Bitrate: 13261 Kbit/s
Jan 27 09:00:01: ERROR: CC: PID:18=5 PID:20=2

There is two common issues: packets loss or packets excess.

Packets excess

Excess packets looks in the tcpdump output as packets from different sources to the same destination:

21:38:42.143839 IP > UDP, length 1316
21:38:42.143868 IP > UDP, length 1316

There is could be two causes:

  • If source address is same but ports are different (in example is 33610 and 24081) then source server sends same channel twice
  • If source addresses are different then more than one server sends packets into the same group

In both cases need to check remote server configuration. If this is not possible or as temporary solution you can drop packets from second source with firewall.

Packets loss

First of all need to check losses and errors on the network interface:

ip -s link show eth0

You need to look at RX Errors. Some network cards provide more detailed information about the nature of the loss:

ethtool -S eth1

Losses can be not only on the network cards of your server. They can also be on the network equipment port. You can find the informaton how to see it in the documentation of the network equipment manufacturer. Where eth0 is an interface name. After the RX-row will be row with numbers. Third number is an UDP receiving errors.

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