[Mikrotik] VPLS Control Word

Chupaka chupaka at gmail.com
Fri Apr 6 06:19:50 CDT 2012


In Windows, you set data payload size for ping, and header is 28 bytes
long. So "ping -l 1472" creates packets with length = 1472 + 28 = 1500
bytes.

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2012/4/6 <butch-mikrotik at ics-il.net>

> 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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