Re: layer 2 fragmentation vs layer 3 fragmentation

Hi All,

There is fragmentation at layer 2 for low speed interface to priortize voice
traffic with small frame size and interleved between fragment of large size
data frame. This feature is called Link fragmentation and interleaving on
PPP incap and have a different name over the Frame relay link... Pls add if
someone remeber the name :)

Thanks
Satinder

On Wed, Dec 22, 2010 at 11:07 PM, Sadiq Yakasai <sadiqtanko_at_gmail.com>wrote:

> I have not heard of L2 fragmentation. I know f L3 fragmentation. I also
> know
> about L4 segmentation though ;-)
>
> Let me give this a try, see if I remember my basics properly here:
>
> Your interfaces have configured MTU (by default or otherwise). Your stack
> on
> the device learns this value and pushes it to the IP layer. When a user
> sends data (from an application, say a web-browser) that is less than the
> MTU value, no fragmentation at L3 occurs. This data gets pushed down from
> L7
> all the way down to the wire without any segmentation.
>
> Now, when the application data is above the configured MTU size, we start
> at
> L4 (since its where the interest really is). L4 does its normal TCP
> windowing and negotiates a window size. Now, this is the L4 segmentation.
> The negotiated window size IIRC is a function of the buffer sizes of the
> application (or stacks) on the 2 ends of the connection (IP source and
> destination). Now the L4 packetizes the data and pushes down to the IP
> layer. The IP layer has already learnt about the MTU from the configured
> value on the interface. This causes fragmentation to occur (+/- the header
> values, ofcourse). L3 hands the packet to L2 and the headers and field are
> populated and the frame is put on the wire.
>
> Someone correct me if I have mixed any part of this please.
>
> Hope it helps abit.
>
> Sadiq
>
> On Wed, Dec 22, 2010 at 5:20 PM, HEMANTH RAJ <hemanthrj_at_gmail.com> wrote:
>
> > Hey i have a little confusion
> > What is the difference between layer 2 fragmentation and Layer 3
> > fragmantation
> > And also tell me when L2 frag is used
> > and when L3 frag is used
> > can anyone share any gud documents regardin this
> >
> >
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Satinder Singh
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