[Mikrotik] VPLS Control Word

butch-mikrotik at ics-il.net butch-mikrotik at ics-il.net
Thu Apr 5 18:01:12 CDT 2012

As I understood it, VPLS Control Word would fragment an Ethernet packet, then reassemble at the far end of the VPLS tunnel.

Without changing any L2MTU settings, when I set ping to do not fragment, I can only get 1472 across. I understand the overhead that VPLS has, but I thought using the Control Word would resolve that issue for me.

MPLS MTU was set to 1508. I increased it to 1518, which I understand is the MTU of Ubiquiti AirOS 5.3 gear.

I increased the L2MTU to 1518 on all interfaces I could. For some reason, on my 493 and 750, I couldn't change the L2MTU, but it was higher than 1518.

I did try my test again, but it still wouldn't let me pass a ping larger than 1472 without fragmenting. I suspect this is because that's all regular Ethernet allows.

With L2MTU and MPLS MTUs set to 1518, it looks like I can traffic an MTU of 1486 (using pings set to not fragment).

I set my Windows MTU to 1518 and pinged through the MPLS\VPLS cloud.

Does this sound right?

What happened to control word auto fragmenting and reassembling?

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