Re: UDP checksum calculation - uses lenght twice ?

Additionally , on RFC793 that starts on last line of page 15 and continue to
page 16 :

The checksum also covers a 96 bit pseudo header conceptually

[Page 16]

September 1981
Transmission Control Protocol
Functional Specification

prefixed to the TCP header. This pseudo header contains the Source
Address, the Destination Address, the Protocol, and TCP length.
This gives the TCP protection against misrouted segments. This
information is carried in the Internet Protocol and is transferred
across the TCP/Network interface in the arguments or results of
calls by the TCP on the IP.

HTH
Arkady

"Arkady Frenkel" <arkadyf@xxxxxxxxxxxxxxxx> wrote in message
news:eYPkpW%238FHA.740@xxxxxxxxxxxxxxxxxxxxxxx
> Hi!
> Both are for the same purpose you can see that in RFC768 ( as in 791 ) too
> Quote from it ( 768 )
> "The pseudo header conceptually prefixed to the UDP header contains the
> source address, the destination address, the protocol, and the UDP
> length. This information gives protection against misrouted datagrams.
> This checksum procedure is the same as is used in TCP."
>
> Pay attention that it not checksum of the data but route info only
> Arkady
>
>
> "R.Wieser" <address@xxxxxxxxxxxxx> wrote in message
> news:u7CGe258FHA.2192@xxxxxxxxxxxxxxxxxxxxxxx
>> Arkady Frenkel <arkadyf@xxxxxxxxxxxxxxxx> schreef in berichtnieuws
>> O$CK7ba8FHA.2716@xxxxxxxxxxxxxxxxxxxxxxx
>>
>> Hello Arkady,
>>
>>> Yes , you have to do that , read about that in RFC793
>>> Arkady
>>
>> I know I *have* to (otherwise the checksum isn't :-) ), but the question
>> is
>> *why*. Why does the checksum use the same length twice ? Is it a
>> goof-up,
>> or is there some sort of logic behind it ?
>>
>> By the way : RFC793 is about TCP, and does not mention UDP at all ...
>> Any
>> hints to where exactly I should look (Allready read RFC768) ?
>>
>> Regards,
>> Rudy Wieser
>>
>>
>>
>
>


.

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