[Mikrotik] VPLS Control Word

Mike Hammett butch-mikrotik at ics-il.net
Fri Apr 6 09:33:34 CDT 2012


Does telling Windows ping to not fragment affect ICMP only or does it affect MPLS as well?



-----
Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com

----- Original Message -----
From: "Mike Hammett" <butch-mikrotik at ics-il.net>
To: "Mikrotik discussions" <mikrotik at mail.butchevans.com>
Sent: Friday, April 6, 2012 9:24:44 AM
Subject: Re: [Mikrotik] VPLS Control Word

I have not gone above 1518 because that is all AirOS 5.3 supports.

Will setting my MPLS MTU above the L2MTU cause the control word process to come into effect?

I'm also somewhat confused with how I was 28 bytes below my MTU to start with, but now I'm 32 bytes below my MTU now that I have adjusted all of my MTU settings.



-----
Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com

----- Original Message -----
From: "Chupaka" <chupaka at gmail.com>
To: "Mikrotik discussions" <mikrotik at mail.butchevans.com>
Sent: Friday, April 6, 2012 9:06:21 AM
Subject: Re: [Mikrotik] VPLS Control Word

So, have you increased Ethernet MTU to something more than 1518?..


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

> Right. I determined that is why I could only send 1472 in the beginning.
> However, shouldn't I be able to send larger packets when the Control Word
> will fragment and reassemble packets? I can only do 1486 now, which is 1518
> - 28 - 4.
>
> ----- Original Message -----
> From: "Chupaka" <chupaka at gmail.com>
> To: "Mikrotik discussions" <mikrotik at mail.butchevans.com>
> Sent: Friday, April 6, 2012 6:19:50 AM
> Subject: Re: [Mikrotik] VPLS Control Word
>
> 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.
>
> --
> Подпись:
> (добавляется в конце всех исходящих писем)
>
>
>
> 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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> > Visit http://blog.butchevans.com/ for tutorials related to Mikrotik
> > RouterOS
> >
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