Software Defined Networks

Wed Dec 4 18:55:17 UTC 2019

On Wed, 04 Dec 2019 17:56:10 +0000, Rod Beck said:

> Can someone explain what is all the fuss? SDN is like the latest telecom
> craze but the articles do a poor job of explaining the advantages. I seek
> concrete examples.

It's called the "cycle of reincarnation".

Way back when, a "router" was a Microvax-II with 2 network cards in it, and everything,
down to the packet checksums, was done in software on the Microvax CPU.

Then we got "routers" that did a lot of the stuff like checksumming in hardware.

Then we went back to software for more advanced features, then the hardware got
smart enough to do it.

For a while, routers were doing IPv4 support in hardware, and the occasional IPv6
packet got tossed towards the CPU. (That was, of course, once they got smart enough
to do something other than "compare first 4 bits == "0100", drop on not-equal". I think
a few boxes didn't even check the first 4 bits and assumed that all packets started
that way, and hilarity and hijinks ensued....

Lather, rinse, repeat multiple times over the past 4 decades.

And now we're seeing "SDN" which just means "Now that the hardware is smarter
and doing a lot of the stuff we used to do in software, the CPU has more free
capacity and we can do new clever stuff in software that we couldn't do
before".

It's *NOT TRULY*  a software-defined network.  If it was, there wouldn't be any
hardware support for checksumming etc, because the checksum to use would be
done in software so it could be easily replaced if you had reason to use a
different checksum algorithm.

(Hint - it's as big a crock as "Software Defined Storage" - which just means
that it's software doing things like the RAID, erasure encoding, and logical
volumes rather than physical volumes, even though the logical volumes are
usually really just RAID-0 concatenations of segments of physical volumes.
Meanwhile, "software defined radio" really means "the physical hardware is
flexible, and software is used to configure it in case you didn't want the standard
channel frequencies in the 2.4 and 5ghz bands".

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