MTU and MSS on WAN connections used for SpeedFusion VPN

Product Discussion
1

When running a SpeedFusion VPN tunnel over cellular and Starlink WAN connections, what should the MTU (and MSS) be set to for each WAN connection?

Should I set all of the MTUs to be the same (i.e., set all to the lowest among them) to avoid asymmetric fragmentation, or set each MTU according to that connection’s capabilities (cellular = 1428, Starlink = 1500)?

And should I set the Starlink MSS to something other than Auto?

For reference:

  • Cellular MTU defaults to 1428. There is no configurable MSS parameter.
  • I have seen recommendations to set Starlink MTU to 1500, but there’s also an Auto setting. Should I use it? There’s also an MSS field and it has an Auto setting.
  • The SpeedFusion Hub WAN MTU defaults to 1440. There is no configurable MSS parameter.
  • I don’t see the ability to configure / “clamp” MSS for a SpeedFusion tunnel, even though it’s recommended to do so here.