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I'm trying to set up a RouterBoard right now, but I don't think this question is specific to RouterBoard.

I have 4 ports all of which need to be on a certain subnet, we will say 192.168.2.0/24. However, one of the four ports must carry this plus another bit of traffic.

This RouterBoard does not allow me to do a "switch group" unfortunately, and that was my first thought. Adding these ports to a "switch group" would cause all traffic to be passed to each port, as if it were a switch, as demonstrated in these two images:

Switch 1

Switch 2

My other thought was to create a VLAN to facilitate this. Unfortunately I cannot use a VLAN because as noted before, one port needs to carry two distinct subnets, thus ruling out the possibility of configuring all the ports as access ports to a VLAN.

I am out of ideas, other than assigning each port a distinct IP on the subnet, which seems very messy and not at all eloquent...

Does anyone have any ideas of how I would be best to configure this?

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Please explain why you need all four ports on the same subnet. There has to be a better topology here... – EEAA Feb 27 '12 at 22:15
Hi ErikA, There are three devices I need to have on an internal management subnet, in addition to one port that will be used for both downstream internet access as well as management IPs. So the one port will need to carry both traffic from 192.168.1.0/24 (which is what we are using for internal IP addressing for internet facing devices) and 192.168.2.0/24 (which is what we are using for internal IP addressing for management devices.) Unfortunately I do not have any extra switches that I can use, so I was hoping to use 3 dedicated ports on the router (in this bridge capacity) plus the one .Thx – sheldon Feb 27 '12 at 22:41
Ok, that's unfortunate. Makes sense now, though. – EEAA Feb 27 '12 at 22:42

1 Answer

up vote 1 down vote accepted

In the Mikrotik world, what you're looking for is a "bridge", which allows routed ports to be added to what amounts to a software switch - create one add each of the ports to it.

However, this won't really fit your need on the port that carries extra traffic; can you expand on what that port is doing? If it's connecting to a device that can understand vlans, you could configure the bridge to be on one vlan of that port, and the 'extra' traffic on another vlan.

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There are three devices I need to have on an internal management subnet, in addition to one port that will be used for both downstream internet access as well as management IPs. So the one port will need to carry both traffic from 192.168.1.0/24 (which is what we are using for internal IP addressing for internet facing devices) and 192.168.2.0/24 (which is what we are using for internal IP addressing for management devices.) Unfortunately I do not have any extra switches that I can use, so I was hoping to use 3 dedicated ports on the router (in this bridge capacity) plus the one .Tyforyourhelp – sheldon Feb 27 '12 at 22:42
What's the dual-purpose port plugged into, and are those two subnets segregated (if so, how)? – Shane Madden Feb 27 '12 at 22:44
It's plugged in to a wireless bridge, but unfortunately the other end cannot see VLANS :( The one subnet originates from this port. The other one is the management subnet that originates with (what is now) a bridge. – sheldon Feb 27 '12 at 22:59
I'm a bit confused - so the two subnets need to share a broadcast domain? Is the management subnet on the wireless bridge, or where do its devices plug in? It might be clearer if you threw a quick little diagram together with how the setup should look. – Shane Madden Feb 27 '12 at 23:10

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