Well David,
I would like to know in which cases this "Don't Fragment" Bit (DF) is
specially set and why ?
Rgds,
B.D.Joshi
On Thu, 7 Jun 2001 [EMAIL PROTECTED] wrote:
> On 7 Jun 2001, at 18:13, Zachary Uram wrote:
>
> > what is an MTU?
> >
> > Minimum Time Up?
>
> Maximum Transmission Unit. A parameter to the outbound portion of
> the protocol stack, it dictates the largest packets that can be sent.
>
> [In *implementation*, it's a parameter to the encapsulate-and-send
> code. In *theory*, it's a characteristic of the virtual circuit;
> odds of errors requiring retransmission rise with packet size, so
> there is some optimal trade-off between error rate and per-packet
> overhead.]
>
> Typical issue is that some intermediate box -- in this case, the
> one that had had AOL on it -- is receiving packets that are much
> larger than its MTU setting. So every received packet that it wants
> to forward needs to be broken into smaller packets, and while it's
> sending the first, it has to put the others somewhere. When it has
> nowhere to put them, things start to break.
> It can ask the sender to send smaller packets, but that request may
> not be honoured. The large packets may have the DF (Don't Fragment)
> flag set, requesting that it not break them up this way. The code to
> break them up could be broken, or the code to put them back together
> could be -- as I recall, part of the issue with the Ping of Death was
> that many implementors never expected their code to have to
> reassemble a fragmented ICMP packet.
>
> David Gillett
>
>
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