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Ethernet driver bug (?) using several MAC addresses (vlan use case) on the integrated NIC


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Posted (edited)

Hello,

 

After several days of debug I put the finger on a very strange issue using integrated Ethernet.

I use my Rockpro64 mostly as a Samba and DNS server.

 

In my network context I implement 2 vlans as vlan interfaces (eth0.10 and eth0.20).

Each of these interfaces needs to use a specific mac address that differs from physical eth0 mac address (it is an important point).

If I use only the physical mac my router is not be able to route correctly between vlans (probably an ivl/svl issue).

 

Under this context I first noticed that when I bring down eth0.20 although using vlan 10 (so eth0.10) connectivity is lost.

I then write a script to gather all needed information (ie. ip link/addr/route/rule/neigh, ping, arping, netstat, ...) ==> no peculiar problem

 

I then add a background tcpdump and, guess what, the connectivity loss didn't occur anymore !

After thinking a bit, I made the assumption that the main difference is the use of promiscuous mode during tcpdump.

 

==> and "bingo" : setting 'promisc' flag on eth0 acts as a workaround.

Also if I do not set a specific mac for vlan and use physical mac leads to no connectivity issue, despite the wrong routing.

 

The key point seems that bringing down a vlan interface unregisters all macaddress from listening process instead only the needed, so the connectivity problem.

 

I don't know if it's a hardware limitation, a driver bug or Armbian issue, but I am open to any fix or at least, any debug hint that helps to narrow down the root cause.

 

Regards.

 

Edited by arnaudf

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