The reason you can no longer configure Ethernet interfaces in slave mode on MikroTik equipment is due to a change in the way MikroTik RouterOS handles link aggregation and bridging from version 6.41 onwards.

Previously, the concept of “master-port” was used to create a software bridge between several Ethernet interfaces, where one interface acted as “master” and the others as “slaves” of the master port.

However, this methodology was replaced by a more efficient and standard bridge-based approach, which offers better performance and is more aligned with networking standards. This change means that bridges are now used to group interfaces, rather than relying on the master/slave port configuration.

The new methodology has several advantages:

1. Simplicity in Configuration: The new method is more intuitive and better aligns with bridging concepts used in other devices and industry standards.
2. Performance improvement: With the implementation of hardware offloading in certain device models, the performance of the bridges can be significantly higher, since some operations can be processed directly by the hardware, reducing the load on the device's CPU.
3. Greater Flexibility: Bridge-based configuration allows greater flexibility in interface management, allowing for more complex and efficient configurations.
4. Configuration Unification: This change unifies the way all interfaces are handled in RouterOS, making VLAN configuration, bridging, and other functions consistent across all interfaces.

To configure a bridge in RouterOS and add interfaces to it, you can follow these basic steps:

Create a Bridge:

/interface bridge add name=bridge1

Add Interfaces to the Bridge:

/interface bridge port
add bridge=bridge1 interface=ether2
add bridge=bridge1 interface=ether3

Here, ether2 y ether3 are examples of interfaces that you want to add to the bridge bridge1.

This bridge-based approach is not only more efficient but also provides a more robust and scalable platform for complex network configurations on MikroTik devices.