Mailinglist Archive: opensuse (3513 mails)

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Re: [opensuse] What's wrong with this IP address?
  • From: "David C. Rankin" <drankinatty@xxxxxxxxxxxxxxxxxx>
  • Date: Thu, 08 Jan 2009 11:07:30 -0600
  • Message-id: <496632D2.2010903@xxxxxxxxxxxxxxxxxx>
Greg Freemyer wrote:
On Thu, Jan 8, 2009 at 10:59 AM, Robert Paulsen
<robert@xxxxxxxxxxxxxxxxx> wrote:
On Thursday 08 January 2009 9:48 am, Robert Paulsen wrote:
On Thursday 08 January 2009 9:36 am, Boris Epstein wrote:
On Thu, Jan 8, 2009 at 10:33 AM, Robert Paulsen

<robert@xxxxxxxxxxxxxxxxx> wrote:
On Thursday 08 January 2009 9:16 am, Per Jessen wrote:

That will show you that the first octet of an ipv4 IP address can range

1 - 223

For classes A, B, and C.
Just out of the curiousity, is there any good rationale for having it
this way?
Look at the bit pattern in the 2nd column in the table that defines the
three classes:


I guess they might be able define additional classes:

D? 1110 XXXX
E? 1111 0XXX

etc. I don't know why it stops at A,B,C, but suspect it might have
something to do with routers and how they can break up address ranges to
direct IPs to different networks. This other bits might take on different

Anyone know any better?

Thinking about this I note the following about "subnets" (defined by bit

A 0XXX XXXX 1111 1111 . 0000 0000 . 0000 0000 .
0000 0000
B 10XX XXXX 1111 1111 . 1111 1111 . 0000 0000 .
0000 0000
C 110X XXXX 1111 1111 . 1111 1111 . 1111 1111 .
0000 0000

After class C we run out of usable subnet bits (can't use all ones as that
would leave no bits to identify individual hosts).

Class D is used for Multi-cast and thus does not support TCP. UDP is
fine. Not real common, but say you have a decent size LAN and you
want to "broadcast" something across it, you can designate one of the
Class D's for that.

I looked into doing NTP style broadcasts that way a few years ago.
The issue is that every switch / router in the lan/wan you need to
forward the multi-cast packets through has to be configured to do so.

I think some brokerage firms broadcast out various news shows to the
traders desktops via IP broadcast mechanisms. I assume they use Class
D packets to carry the UDP packets. (ie. If a trader wants to see
what Fox News is showing, they have a video app on their desktop that
can tune into the multi-cast packets and show it to them.

Class E I know of no use for, but I would not rule it out.


If you look at your lan with ntop and you have windows machines hanging around,
you will see a lot of UDP traffic with Just google that IP and
you will get a feel for why you see that traffic. Evidently M$ makes a lot of
use of it.

David C. Rankin, J.D.,P.E.
Rankin Law Firm, PLLC
510 Ochiltree Street
Nacogdoches, Texas 75961
Telephone: (936) 715-9333
Facsimile: (936) 715-9339
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