Messages in this thread | | | Date | Wed, 17 Sep 2003 16:06:43 +0200 | From | "Ihar 'Philips' Filipau" <> | Subject | Re: Incremental update of TCP Checksum |
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Richard B. Johnson wrote: > > This is all wonderful. This assumes that the stuff being modified > in the packet is on well-defined boundaries, seldom the case when > you are re-writing packet data, but certainly the case if you > are re-writing an IP address. > > Also, modern switches do not rewrite checksums using software. ^^^^^^^^ > Therefore, they do not use a re-write algorithm as stated by > others. The checksum gets calculated "for free" during the > hardware transfer to an output holding FIFO. It is done using > an ASIC with the appropriate adder and "stumble-carry". >
It depends on definition of software. It is so hard to draw parallel especially when what looks like controller runs some flavour of Linux from some embedded flash ;-)
Actually some switches do alter header _before_ they have received payload. Just to be able to start rx without waiting for payload to arrive completely. Sometimes low latencies (even on narrow bandwidth links) are _that_ important...
-- Ihar 'Philips' Filipau / with best regards from Saarbruecken. - - - - - - - - - - - - - - - - - - - - * Please avoid sending me Word/PowerPoint/Excel attachments. * See http://www.fsf.org/philosophy/no-word-attachments.html - - - - - - - - - - - - - - - - - - - - There should be some SCO's source code in Linux - my servers sometimes are crashing. -- People
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