VLAN behavior and bridge

RouterOS General
1

Hello,

Ive found a behavior and I would like to ask anyone that knows it already and if there are some documents describing it, please.


Consider two devices connected via ethernet:

Device A (ether1) <-------- ethernet cable ---------> (ether1) Device B

Then, we create a addressed VLAN between them with some network i.e. “192.168.0.0/30”:

Device A (ether1[vlan1:id2]) <-------- ethernet cable ---------> (ether1[vlan1:id2]) Device B

IP 192.168.0.1/30 at vlan1 on device A and IP 192.168.0.1/30 at vlan1 on device B. So, I can ping each other device.

The question is: Why we stop pinging each other after adding the interface ether1 as a port of some bridge? There is no ARP? Thanks in advance.

2

In my experience, the physical interface that the VLAN is on cannot be part of the same bridge as the VLAN itself. I’m not really sure why, but whenever I have tried it, all traffic appears to come from the physical interface, and not the VLAN.

Maybe someone else knows a way around this, but I haven’t been able to find one.

Also one thing you are going to want to enable on your bridge if you haven’t been is STP or RSTP, especially if you have multiple VLANs on one physical interface all part of the same bridge.

3

If the physical interface is part of the bridge, then all the vlan information is sent along with it. If you want 2 ports to have the same vlan information, bridge them and assign the vlans to the bridge interface.

It doesnt function exactly like a switch.

4

I got it. Thanks for the answers. Ive found this VLAN behavior by accident as I didn’t ever worked with VLANs yet. But the real problem witch lead myself here was the MPLS interfaces MTU. Ive found somewhere people calculating MTU for MPLS as 1526 instead the default 1508, but for some reason I didn’t understand yet the value 1526 does not work here. BWTest does not even work for downstream, but upstream works ok. With 1526 MTU I can’t ping with packets larger than 1462, but with 1508 MTU I can ping with packets 40k+ larger. Basically:

Internet 10/100/1000 – MPLS BGP VPLS – PPPOE 1480 – Host.

Sry for OT.
Ozelo

5

Look at examples how MTU should be calculated
http://wiki.mikrotik.com/wiki/Manual:Maximum_Transmission_Unit_on_RouterBoards#Simple_Examples