linux – All ports be down when ethernet interface is down

I have a network problem in my system.

(unmanaged switch)
├──AP(router) — WAN
└──my device

All linked by ethernet,
and my device uses RT5350 as HW, U-BOOT 2017 and OpenWRT 18.06 as SW.

The problem is that all ports stop sending packet when my device is booting.

As a bunch of tests, I figured out that

  • Unmanaged switch stop sending right away (CCTV2 cannot send packet to WAN)
  • AP stops after few seconds (CCTV1 cannot send packet to WAN), but can reply to ICMP ping from wireless medium.
  • Holding my device to its bootloader sequence(like entering tftp) makes same problem
  • ifconfig eth0 down after entering OS on my device makes same problem
  • ifconfig eth0 up, all were recovered right away
  • AP’s mac address table has been lost whenever it stops
  • AP received RX-Pause storm from my device right before stopping during eth0 interface were downed!
  • But my device sends no packet at all, at least on wireshark, tcpdump, ngrep.
  • Managed switch (CISCO SG220P, SG300, Netgear GS308E, Soltech SFC400GM) had no matter.
  • It has nothing to do with STP, CDP, LLDP. I turned off it on SG220P but it works well.

What is the reason of this problem?
And how could I fix my network and device?

Thank you.