Security Basics: Re: TCP/IP CRC question

[Miles Stevenson <miles () mstevenson org>]

Jorge,

I see that you have a lot of different, sometimes incorrect answers to this 
already. Alex was correct with his response though. 

Think of it like this...

When the IP protocol was designed, it needed to run over any underlying 
technology, from Ethernet, to Token Ring, to whatever. Basically, it couldn't 
have been designed to "trust" the lower layers that it was getting correct 
data, which is why it implemented its own checksum. TCP took the same stance 
when it was designed, as did protocols on different layers of the stack.

So, while you are right that it IS redundant to perform  checksums on each 
layer of the stack instead of just doing it on one layer that encapsulates 
the whole packet (such as Ethernet), the protocols had to take this approach 
to remain independant of the other protocols.

Good question though.

-- 
Miles Stevenson
miles () mstevenson org
PGP FP: 035F 7D40 44A9 28FA 7453 BDF4 329F 889D 767D 2F63

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