Re: TCP/IP CRC question

[Jonathan Loh <kj6loh () yahoo com>]

So that the other layers can do validation checking.  Speeds things up.  So
everytime you see a packet you do not have to read the whole thing.  You can
just read the header and if that's bad you know the whole thing is bad.

--- Jorge Mendez Bonini <jlmb () cableonda net> wrote:

> I've been reading about the TCP/IP protocol stack (TCP/Ilustrated Vol1 
> by Richard Stevens) lately and since Ethernet is quite common nowadays 
> almost all link layer examples refer to it (I also checked Douglas Comer 
>   Internetworking with TCP/IP vol1).
> I tried searching RFC but found it very time consuming without good 
> results (maybe I'm not used to it...yet)
>
> The Ethernet Frame contains a field known as FCS which contains a CRC.
> Now, my question is:
> If the CRC is generated from DATA field among others, What's the point 
> of using checksums on the upper protocolos (IP checksums etc..)?
>
> Thanks for your time.


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