Re: TCP/IP CRC question

From: Jonathan Loh (kj6loh_at_yahoo.com)
Date: 10/06/04

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    Date: Wed, 6 Oct 2004 13:15:20 -0700 (PDT)
To: Jorge Mendez Bonini <jlmb@cableonda.net>, security-basics@securityfocus.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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