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Altera_Forum
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14 years ago

InterNiche stack drops packets when ip_chksum field is set to 0xFFFF

For our embedded products we use the iNiche stack. We have several systems running and we see occasionally network packets being dropped by the iNiche stack. We have the impression that it is somehow...
Altera_Forum's avatar
Altera_Forum
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14 years ago

Below the response we received via our EBV FAE

Section 4 of RFC 1624 gives an example where a checksum is computed using the equation from RFC 1141, and as such incorrectly generates a checksum of 0xFFFF, whereas the checksum when calculated from scratch would be 0x0000. This would indicate that Windows 7 system is possibly generating a checksum using methods in RFC 1141 rather than the updated recommendations for incremental checksums in RFC 1624, derived from the base specification RFC 793.

Having said that, Section 5. of this document acknowledges that systems may not agree on the checksum in this case, with a recommendation to work around systems that generate 0xFFFF by modifying the checksum checking methodology used.

In summary, I can see this issue having two main points:

(a) The Windows 7 machine does not generate RFC 793-complient checksums. It may use the methods in RFC 1141 which was updated to correct for 0xFFFF checksum "