Re: layer 2 fragmentation vs layer 3 fragmentation

Although it is seem like TCP negotiate MSS and window size , it do not
negotiate at all!
each side send his own supported size for MSS and window telling the remote
side what he is permitting him to send.

And about window size and Ack relation that is also wrong, if an entire
window would have been lost that is a lot of data, Ack is sent from
the receiver side on every 1 MSS size of data, the sender retransmit in case
a RTO retransmission time out expired and he did't got an Ack, the Window
size is a buffer the max of data a unit can process before it get an Ack's
on the full window (buffer) amount.

On Wed, Dec 22, 2010 at 8:02 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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> > >
> > > Yours Friendly,
> > > HP HEMANTH RAJ
> > > Cisco Systems Inc.
> > >
> > >
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> > >
> > >
> > >
> >
> >
> > --
> > CCIEx2 (R&S|Sec) #19963
> >
> >
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