MSS-clamp equivalent for udp?

RouterOS General
1

Hello:

I have a HD HomeRun tuner plugged into a mikrotik box with an EoIP tunnel that runs through another wireguard tunnel before getting to its destination. The HD HomeRun is a TV tuner for picking up over-the-air TV and converting it into a udp stream. There is no way to change the MTU on the device. As a result, when watching programming with higher bitrates, I run into a lot of packet drop issues because of the tunneling. Previously, the node upsteam of the Mikrotik doing the EoIP tunnel was a pfSense router, which was one end of the wireguard tunnel, with a Mikrotik LTE device as the “client” device. With pfSense, I was able to adjust the MTU down through the tunnel.

I just replaced the pfSense router with Mikrotik, and so far, I haven’t been able to replicate that behavior. I want any packets too large for the tunnel (EoIP + wiregard, I believe it was about 1370) to be segmented. Not just TCP, but all packets.

How do I do this on Mikrotik?

Thanks!

2

Just manually override MTU setting of EOIP interface. EOIP does fragment/defragment frames, which are otherwise too large to fit the outer MTU, if needed.

3

Ok, thanks! I think I’m having larger MTU/MSS issues, as its not working, but I’ll post a separate topic for that.

4

Set EoIP to 1500 MTU. It will fragment but almost certainly needed since I doubt the HDHomeRun does PMTUD. Generally there 7 MPEG frames per RTP packet, so I’m guess it like needs 1400 MTU (or more if FEC is used). Now, the WG tunnel if it’s going through LTE likely have to be lower than the default 1420, I’d focus on making sure WG MTU is right as both being wrong is 4x fragmentation, not 2x.

Also make sure the Don’t Fragment is unchecked.