Nano - MTU doesn't apply for streams

Pearl Nano
1

The MTU parameter in the network page doesn’t seems to work/apply.
We need to reduce the MTU because we use IPSEC/GRE tunnels in the network path between the Nano and the receivers.

When captured using wireshark, the packets sent by the Nano are the same size regardless of the MTU set in the network page.
Here are the packet size we saw, with a MTU set at 1400:
MTU stream RTP : 1328
MTU stream UDP : 1316
MTU stream RTSP(TCP) : 1460
MTU stream RTSP(UDP) : 1472
MTU stream HLS : 1460
MTU stream SRT : 1332

The Nano we use is in version 4.24.0

2

The MTU settings would represent the maximum size of packet that can be sent. I believe it can be less than the maximum, but being slightly more might be strange. If you reduce the MTU even further does the data follow this?

3

I agree that it can be less than maximum but even if I reduce the MTU to 1000, the packets size stay the same as posted above.

My method for testing is :

  • Change the MTU on the Nano
  • Reboot it
  • Start streams (RTP/UDP/SRT)
  • Capture the packets on the switch port where the Nano is connected
4

Thank you - I will pass this to the engineers and see what they think. I have also created a ticket for you, and will reach out to you via that thread.

5

General Update:

There is indeed an issue when applying MTU settings on Pearl Nano and it is planned to be fixed in an upcoming firmware release - if you would like to be updated, please submit a ticket to support@epiphan.com