They do not override each other - these are different settings and each is used for different purposes. In order to control the size of MPLS frame you only have to change MPLS MTU.Will setting the MPLS MTU under MPLS Interface override the MTU settings under the general tab (winbox) for the individual interfaces?
You add 22 to 1500. So you can set MTU (but you do not have to) or MPLS MTU on 433 to 1522 (assuming you do not use VLAN). In order to forward VPLS encapsulated frames without fragmentation, you need MPLS MTU at least 1526.Do I add the 22 extra bytes to 1518 or 1500? in other words can i set the MTU for ether1 on a 433AH to 1540? and is that what i need to do in order for VPLS links to accept 1500 byte packets without fragmentation.
The MTU is actually about transmitting packets over interface. "/interface" MTU is for layer 3 (IP) packets - IP protocol will not send IP packets larger than this MTU for transmission over interface - it will either fragment or drop. "/mpls interface" MTU is for MPLS packets - MPLS will not send packets (including MPLS labels) larger than this. And that's all about MTUs - e.g. you do not have to set MTU for ethernet interface to 1508 in order to add "chained" VLAN interfaces to send QinQ frames over ethernet interface.The MTU for each interface is in effect when non-mpls packets are received on an interface, and the MPLS MTU is used for MPLS packets, correct?
Bridge will not fragment packets.Since im not running MPLS on the equipment that makes the wireless links between the RB1000's (the rb433ah boards), how will they treat frames that are bigger than the MTU hardcoded under the tab for ether1 (1500) will they attemt to fragment, even though they do not understand the content of the packet?
Well, the process of bridging currently is somewhat inconsistent with overall "MTU policy" - when bridging (which is action happening at layer 2 and therefore should have nothing to do with layer 3 MTU), bridge actually checks that packet (minus link layer header) does not exceed "/interface" MTU, so you are right. As to bridged interfaces - currently you have to set their "/interface" MTU to value to accomodate any VLAN tags or MPLS labels. In your case this means that "/interface" MTU for bridged interfaces must be set to the same value as "/mpls interface" MTU on your MPLS routers.Since they work as bridges i assume they invoke the MTU for the interface. Or will they simply drop any packet that exceeds the MTU of 1500 since the "payload" beyond the L2 header is MPLS ?
As long as you configure "/interface" MTU on bridged interfaces to be the same or bigger than MPLS MTU on MPLS routers, you should be OK.Since the boards i use for bridgeing the RB1000's together, can only achive a 1522 MTU and i really need 1526 in order to avoid any fragmentation, should i just stick with the RB1000's @ MPLS MTU=1508 and the up the MTU of the 433ah boards to 1522 on ether1? (to allow for future VPN use)
Is that the best solution?
Interface GigabitEthernet 1/0/1 mtu 9216 !
Yes. L2MTU of 433 is not big enough to be able to forward VPLS frames w/o fragmentation.After working a while I think I will not be able to transfer the customer VLAN with tag over the VPLS-tunnel because the L2MTU of RB433AH (in MPLS router mode) is to low. Is that right?
RouterOS VPLS supports frame fragmentation, so you can still use VPLS.Is there another way to transport a VLAN trunk with IP-traffic inside between the edge routers (if it is beccessary with fragementation)?
It changes what ethernet protocol value is used for VLAN encapsulation, nothing more.What does the "User Service Tag" in VLAN configuration to?
Probably, but then your network core must be bridged, instead of routed.IS Q-in-Q a solution?