MikroTik local link up / down on high traffic

One of our RouterBOARD routers – MikroTik RB750 (mipsbe with Atheros 7240 switch) running the version v6.35.2 (latest version) have been constantly crashing on high network load. One particularly interesting note is that it crashed on traffic that goes through the internal switch but not on other traffic.

The log file shows the following pattern:
may/13 21:23:17 interface,info ether1-gateway link up (speed 100M, full duplex)
may/13 21:23:17 interface,info ether2-master-local link up (speed 100M, full duplex)
may/13 21:23:17 interface,info ether4-slave-local link up (speed 100M, full duplex)
may/13 21:24:21 system,info sntp change time May/13/2016 21:23:38 => May/13/2016 21:24:21
may/13 21:26:22 interface,info ether2-master-local link down
may/13 21:26:22 interface,info ether4-slave-local link down
may/13 21:26:24 interface,info ether2-master-local link up (speed 100M, full duplex)
may/13 21:26:24 interface,info ether4-slave-local link up (speed 100M, full duplex)
may/13 21:29:16 interface,info ether2-master-local link up
may/13 21:29:16 interface,info ether4-slave-local link down
may/13 21:29:17 interface,info ether2-master-local link down
may/13 21:29:18 interface,info ether2-master-local link up (speed 100M, full duplex)
may/13 21:29:18 interface,info ether4-slave-local link up (speed 100M, full duplex)
may/13 21:36:01 interface,info ether4-slave-local link down

A little search on the internet shows that we are not alone. Port flapping is widespread in MikroTik world. There are many reports with the similar problem dating back to 2011, but there are no solution:

My guess is that switch chip is broken / dead /malfunctioning / buggy. Or the switch “part” of MikroTik router is sensitive to voltage / current changes.

But anyway, we solved this by disabling the switch and changed each port to different subnet (Bridging also may work). Now all the traffic is sent through the CPU, and even when MikroTik advertises, that switch have wire-speed, we noticed that traffic-through-CPU have even better performance.

One thought on “MikroTik local link up / down on high traffic”

  1. Hi, I have read your post when searching for a fix, ans now I’ve implemented what u say about disabling switch and using bridge (it was the opposite of recommended setup by mikrotik about using hardware nor cpu, but lets see).

    Later I will post my results.

    Best regards,

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