[ih] why did CC happen at all?

[Brian E Carpenter]

On 03/09/2014 04:59, Craig Partridge wrote:
>> So that weak 16 bit UDP checksum can help catch this stuff.  I wonder
>> how many corrupted files were created with NFS and broken ethernet
>> hardware?
> 
> Lots and lots.
> 
> At one point, a late generation of BBN Butterfly computers had a low voltage
> problem on a bus that would cause some bytes of a DMA from network adapters
> to be garbage.  Trashed the NFS filesystem, as I recall, about once a week.

Yes, it really wasn't (isn't?) an uncommon problem. I think I first saw it
in CAMAC crates in the 1970s.

All PCs have error-correcting redundancy in their RAM, right? Er, wrong.
Bit corruption in PCs really happens.

The decision was taken in IPv6 to remove the header checksum but make the
UDP checksum mandatory, because people felt the tradeoffs had changed
since IPv4 was designed. But nobody suggested trusting layer 2 and/or
DMA, because they weren't and aren't trustworthy.

    Brian