Re: [LI] two ques

[Chetan Kumar S <cheetank@xxxxxxxxxxxxxxxxx>]

On Thu, 4 Nov 1999, Sharad Joshi wrote:

> On Thu, 4 Nov 1999, Chetan Kumar S wrote:
> + 
> + On Thu, 4 Nov 1999, Sharad Joshi wrote:
> + 
> + > 
> + > 0.  *WHY* the *minimum* ethernet frame size is 64 bytes. Any rational  
> + >     behind this? This means that *at-least* 46 bytes of data *must* be
> + >     present in the ethernet frame. (Even if there is not much data, that
> + 
> + How is that 46 bytes free, 14 (ether header) + 20 (IP) + 8 (UDP) = 42
>                              ^^^^^^^^^^^^^^^^^
> The data part does not include header and trailer. With these, the minimum
> ethernet frame size is 64 bytes (14 + 46 + 4)

Ofcourse this as I mentioned assuming TCP/UDP over IP, so if I pick up a
ethernet packet and if the size is not atleast ethernet header + IP header
it would be wast, as I can not process further, that is what I meant. And
this doesn't answer ur question ofcourse..

> + >     are silent on this.
> + 
> + This should be OK, pseudo header will take care that I will have proper
> + port numbers (also sequence numbers, ack numbers in tcp). This is more
> + serious in terms of TCP where a loss in seq number can get you no
> + where. And as you know UDP checksum is not mandatory.
> 
> Well, AFAIK, checksum is used to preserve data integrity only. Is it used
> for anything else? If that is the case, what is that 'else'? And if this
> is not the case, then calculating checksum only over the respective
> headers, exclusive of pseudo header, shud suffice, no?

No, the rational nehind this would be if the UDP header is corrupt, where
will U pass the data, I mean which port, and what do I do with a DATA that
is fine, but delivered to wrong port/process.. 

This things got nothing to do with LINUX, so please take it off the
mailing list... may be if intrested continue on my personal mails..

-Chetan S

> 

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