Changed RouterOS nic driver from e1000 to virtio to fix RouterOS MTU bug

[NoifP]

On RouterOS 6.x.x with e1000 network driver vlan sub-interfaces with MTU > 1500 do not function properly (they have an MTU of 234 !). On RouterOs 7.x.x they function fine.

I tested with both virtio and vmxnet3 drivers.

• vmxnet3 drivers crashed qemu when the MTU was changed in RouterOS (resulting in a router reboot).

• virtio drivers worked and fixed the issue with MTU. Tested on RouterOS 6.45.9 and 7.12.2. Did not observe any issues while testing.

  Mikrotik recommend virtio driver for proxmox (also QEMU based) so it should be fairly safe: https://help.mikrotik.com/docs/display/ROS/CHR+ProxMox+installation

[hellt]

👍

[NoifP]

@hellt I have since found out that this has the side effect of breaking LACP. It appears that Mikrotik CHR does not transmit LACP when using virtio driver (but works fine with e1000 driver). I observed this when packet capturing on the CHR itself with same firmware, same config and only changing the NIC driver.

It may be a conscious decision by Mikrotik to prevent CHR breaking underlying virtual infrastructure with stray LACP packets (or it may just be a bug). Either way for my use case my labs do not work without jumbo MTUs and bonds can be easily reconfigured to be active/passive without needing negotiation.

For anyone else who comes across this LACP issue with Mikrotik RouterOS CHR on QEMU maybe you can reconfigure all bonds on the CHR by appending the following to your config: /interface bond set [find] mode=active-backup

[hellt]

Thanks I wonder if you tried recent versions of chr?

[NoifP]

Yup, I tried on v6.x.x and v7.x.x with the same result.

[hellt]

alright, at least we follow the official documentation regarding the choice of a driver. We can make a note in the docs covering the LACP thing