I have two 24-Port switches with two extra GigaBit ports - Port 25 and Port 26.
On Mikrotik machine, I used the bridge interface to join all ethernet interfaces together and assigned the 192.168.0.1/22 address to it:

Bridge <= ether1, ether2, ether3, ether4
PPPoE out <= ether5

Both switches have assigned IP addresses:
Switch A - 192.168.0.100 (mac: 01:23:45:67:89:00)
Switch B - 192.168.0.200 (mac: 01:23:45:67:89:FF)
(They use web-interface configuration, so that's why they have MACs and IPs)

Because I want to use both gigabit ports (per switch), I had to use VLAN Groups (VLAN ID:1 and VLAN ID: 2)
Odd port numbers use VLAN ID:1
Even port numbers use VLAN ID:2

I did the same with the other switch (Switch B).

Everything works fine, until I plug one of the switches in the RouterOS machine. Lights blink like nuts, and console starts freezing on the RouterOS machine until it shuts down with an error message - something about looping packets ...

Ok I understand what's going on, the switch (I plugged in) transmits and receives it's own packets through the bridge.
Is there a way Switch A (and B) could be configured so it would ignore it's own packets? Because I still want to use the bridge function... Or is there a way to solve the problem with Mikrotik (Bridge Filters ...)?

Here the network diagram, for easier understanding:


Here's are some screenshots of the Level-one switch web interface configurations:


And here's the Level-One GSW-2472TGX manual.

I hope you can help me with this problem.

VLAN tagging wil not solve your problem. Spanning Tree will.

If however, you want a 2GBit link between the two buildings then setup a trunk between the two switches using the Gigabit interfaces on the switches. Remove all but two of the NICs from the router, one connects to a 100MBit switch port, the other is for the ADSL link.

A simple solution is best. In this case it will also be considerably faster.

Regards

Andrew

Thanks andrewluck for the advice.

It is not a 2GBit link between two buildings that I want ... but a mass storage server is also connected to the Mikrotik machine (not shown in the scheme). We're going to use it for document storage, and it has a 1GBit link to the "main bridge".

But I think / hope STP will sove the problem. I don't know much about it, yet. But there's a lot of good documentation online, I'll start with wikipedia http://en.wikipedia.org/wiki/Spanning_tree_(networks)
http://www.mikrotik.com/docs/ros/2.9/interface/bridge

One question though, does the hardware have to support the STP? (Switches, network adapters?)

Thanks again.

All managed switches will support STP. NICs do not have to be STP aware.

You need to look again at the design of your Core network. The job of the Core network is to switch user packets to their destination as quickly as possible with minimum delay. In your case, this will mainly consist of getting packets to and from the NAS.

The PCI bus that your NICs are plugged into in the Mikrotik box just isn't capable of keeping up to the throughput of 5 Gigabit cards and it will be a major bottleneck. Additionally, as a software device, it just isn't in the same league as hardware ASIC switching.

Better by far to plug the NAS directly into a port on one of the switches and use the MT as a firewall/Internet gateway.

Regards

Andrew

Today I turned on the STP protocol (in the bridge interface), and it didn't do any good.

Everything connected to the switch didn't work anymore, but at least this time, the mikrotik machine didn't start freezing.

Is there any other way to do that, with the same setup?

I'd get rid of the dual gig-e feeds. The MT (as said before) wont pass 5 gig anyhow. What you are doing is bridging vlan1 and vlan2 together to create a network loop.

Are the gig-e links copper or fiber?

I'd get rid of the dual gig-e feeds. The MT (as said before) wont pass 5 gig anyhow. What you are doing is bridging vlan1 and vlan2 together to create a network loop.

Are the gig-e links copper or fiber?

Copper - cat 6...

ehh, I've disabled all VLAN features on both switches, and enabled RSTP on mikrotik. Mikrotik assigned roles for those bridge ports: two ports are "designated ports", and other two are "backup ports". I don't even care for the bandwidth anymore... It's good the way it is now

Thanks for the help.