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Re: This (new to me) ip thingy




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On Tue, Oct 03, 2017 at 04:36:12AM -0400, Gene Heskett wrote:
> On Tuesday 03 October 2017 04:17:49 Reco wrote:

[...]

> > Multicasts are not anything that *anyone* should configure.
> > The whole idea of them is that your L2 network segment configures by
> > itself.
> >
> > Reco
> 
> In that class A? Not even my isp has anything there.  Its not a pingable 
> address from here as I believe dd-wrt would stop it, nor does whois have 
> a clue. NSA back door?  Damnifiknow. Traceroute gets zero response too.  
> So what or who is it?

Reco's right. Have a look at [1], heck, spend an afternoon at your local
lib thumbing through R.L.Stevens "TCP/IP Illustrated". This afternoon
will pay for itself in terms of time within the next half-year, believe
me.

The address range 224.0.0.0/4 (in binary: 1110xxxx xxxxxxxx xxxxxxxx xxxxxxxx,
if my skills haven't betrayed me) is reserved for "IP multicast". One
source, many receivers. Think radio or TV broadcast. The sender sends
a packet once, and each router where traffic might split "knows" behind
which branch there are "interested" receivers (there's a protocol to
"register" interest). This router is then responsible for duplicating
packets. The idea is to not send the same packet 10000 times over the
same link.

Needless to say that even the idea of pinging such an address is
somewhat... mind bending :-)

Cheers
[1] https://en.wikipedia.org/wiki/IPV4#Special-use_addresses

- -- tomás
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