NanoPC-T3, bad performance of router functions

[CodeNemo]

I set up NanoPC-T3 as a router, the upsteam Ethernet port is connected to a router. However, the bandwidth drops dramatically whatever I’m using IPTables or network bridge to forward the data. This doesn’t happen on the other SBCs I have. How can I solve it?

Edited December 2, 2018 by CodeNemo