Re: [LI] two ques

[Chetan Kumar S <cheetank@xxxxxxxxxxxxxxxxx>]

On Thu, 4 Nov 1999, Sharad Joshi wrote:

> Hio,
> 
> I posed these ques in different forums, but did not get any satisfactory
> reply. I know this is not the best stage to raise these ques, but i am
> sure any serious network software developer would be interested in these
> at some point of time... Now the ques.
> 
> 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
filled up ofcourse assuming tcp/udp over IP, if you are looking at
something else??.


>     *must* be appended with zeros to make it 46 bytes).
> 
> 1.  *WHY* is a pseudo header used for calculating checksum in TCP/UDP
>     headers. Is this not a overhead. Any specific reasons for this? RFCs 
>     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.


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