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John Boxall
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Creator and sole curator of tronixstuff.com
Creator and sole curator of tronixstuff.com

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Anniversary: the network is down! The Arpanet was connected by these IMP machines - routers which sat in front of the connected machines and networks. On this day in 1980 the Arpanet suffered its first major outage, as each IMP got bogged down.
A contributing cause was the overflow of a 6-bit sequence number used in the broadcast routing updates, and the flood of update messages preventing the keepalive messages from getting through - so each node took itself off the network. When it rejoined, the sequence numbers would not help it ignore old routing updates, and the problem would recur.
One errant IMP, it turned out, was sending bad updates, so all other machines were sent a patch to ignore it - over the flaky network!
The root cause was that checksums were (re)calculated in software sometimes on bad data - checksumming being too expensive to apply throughout. Bad hardware could then create harmful packets which were given good checksums. The next generation of IMPs had checksumming in hardware.
...
"For a period of several hours, the network appeared to be unusable, due to what was later diagnosed as a high priority software process running out of control. The immediate cause ... was a rather freakish hardware malfunction (which is not likely to recur) which caused a faulty sequence of network control packets to be generated. This faulty sequence of control packets in turn affected the apportionment of software resources in the IMPs... Connections which already existed were summarily broken.
A flood of phone calls to the Network Control Center (NCC) from all around the country indicated that the problem was not localized, but rather seemed to be affecting virtually every IMP.
We tried manually restarting a number of IMPs in our own building. This procedure will often clear up problems... The IMPs which were restarted worked well until they were connected to the rest of the net, after which they exhibited the same complex of symptoms...
"
- http://www.faqs.org/rfcs/rfc789.html#b

Here's an Arpanet map from 1980:
http://mappa.mundi.net/maps/maps_001/

via +Ken Harbit
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All GSM Shields and modules in stock are now $10 inc GST until sold out... https://tronixlabs.com.au/dumpster #arduino
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SALE! 10% off orders over $100 until Tuesday 7th June with discount coupon code JUNE16
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MOVING SALE - 11% off storewide with discount coupon code "ELEVEN" - expires 20/3/16 #arduino #raspberrypi
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Hacker publishes a Rosetta Stone of sorts for getting business done in Shenzhen
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Free delivery Australia-wide on all orders received this weekend - no coupon required! Visit http://tronixlabs.com #arduino #raspberrypi
Tronixlabs
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