Re: layer 2 fragmentation vs layer 3 fragmentation

Thats correct! Its the MSS and not the window size there - thanks for the
correction.

On Wed, Dec 22, 2010 at 6:02 PM, George Goglidze <goglidze_at_gmail.com> wrote:

> Hi,
>
> L2 Fragmentation:
> Frame-Relay - FRF.12/FRF.11
> MLPPP - Fragmentation and Interleaving
>
> And when TCP negotiates a Window size, that has nothing to do with
> fragmentation.
> That only means that one end is gonna send that window size before it'll
> expect ACK from the other end.
>
> For the matter of MTU, TCP negotiates MSS size, which is by default 1460B.
> That together with IP 20B and TCP 20B makes it 1500B.
>
> Regards,
>
> On Wed, Dec 22, 2010 at 6:37 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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>> > Cisco Systems Inc.
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>>
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>> CCIEx2 (R&S|Sec) #19963
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>

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