We have a debian 10 linux server configured with a bond on two interfaces, based on Promox PVE.

Seems to work but we get alerts on a monitoring system (netdata) regarding packet loss so I am wondering what kind of setup if any I need to enable in my mikrotik (RB3011UiAS).

I've read best performance recomendations are on the 802.3ad (aggregation) mode but I so far understood requires a special support on the router. Currently we have a 1Gb unmanaged switch in front of the connection to the mikrotik, so both interfaces connect to a switch and this switch to the mikrotik, so not sure which modes would be supported, if the issues are related to this configuration on the server side or I need something enabled on the mikrotik to support the bonding in general, or specifically the mode 5.

Thanks.

Principal use case of bonding is to use multiple physical connections between adjacent L2 nodes ... in your case that would be between server and switch (one bond) and between switch and router (another bond, both bonds operating independently). The dumb switch will mess with any bonding you'll try to set up between server and router because it'll try to cross-connect both links which is not expected by any of bonding algorithms.

Thanks. That's what I thought. In the case I can connect both nics of the server directly to the mikrotik (LAN ports), do I need to configure port specific options to those? Do I need to enable something for Mikrotik to support/understand those two are "a" bond interface?
thanks.

Thanks. That's what I thought. In the case I can connect both nics of the server directly to the mikrotik (LAN ports), do I need to configure port specific options to those? Do I need to enable something for Mikrotik to support/understand those two are "a" bond interface?
thanks.

You have to remove the interfaces from common bridge and configure them as bond members. Then add the bond interface to bridge. How exactly depends on router HW type. This article should help you get started.
Bonding type should be same on both ends (router and server).