[FS#612] WAN to LAN leakage on MT7620 devices

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - Kristian Evensen (kristrev) 

Attached to Project - LEDE Project
Summary - WAN to LAN leakage on MT7620 devices
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - High
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - I am currently testing two MT7620 devices - the ZBT WE826 and the Sanlinking D240. During the first seconds of the boot, I see that packets leak between the WAN and LAN ports. Typically, this results in clients receiving a DHCP reply from my upstream router, rendering the clients without connectivity when the switch is properly initialized. I have also tested with the default firmware and do not see this behavior. Also, if I stop the devices in the bootloader, then packets do not leak until I resume boot again.

In order to try to solve this bug, I have tried to port some (at least to me) missing steps from the bootloader switch code and to the mt7620 switch driver in LEDE. This did not have an effect, at least not on the packet leak. A work-around I have found is to update u-boot and remove the input delay, so that the device will boot immediately. However, this is quite cumbersome to install and not very reliable. I suspect my luck with this work-around is more due to the timing of the DHCP clients in Ubuntu and Windows 10.

Does anyone have any idea as to what could be wrong and where to start looking?

Thanks in advance for any help.
   

 

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=612