Re: IP/Networking... 70-291.
- From: "Phillip Windell" <philwindell@xxxxxxxxxxx>
- Date: Wed, 24 Oct 2007 12:28:49 -0500
"Robert Bollinger" <RobertBollinger@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
message news:A0CA364B-6378-4ED4-B48A-16C7B366282E@xxxxxxxxxxxxxxxx
I am trying to understand that following information that comes from the
70-291 book. this is on chapter 2-33 just above the figure 2.5.
It says this: if i have 131.107.0.0/16 ... that i can subnet that like
this:
131.107.1.0 /24 << Router A, 131.107.2.0 << Router B, 131.107.25.0 /24
This i understand just fine... however...
It then says... Hosts external to the orginization then access hosts
within
the orginization using the /16 address.
It is called SuperNetting.
[Router #1]
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[Router #2]--------<LAN 131.107.1.0/24>
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<LAN 131.107.2.0/24
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[Router #3]----------<LAN 131.107.25.0/24
Since all three LANs "fit" inside of 131.107.0.0/16 the [Router #1] only has
to know to send any thing contained within 131.107.0.0/16 to the [Router
#2]
The [Router #2] will already know what to do with it from that point.
So you are "SuperNetting" all three LANs into a single route between [Router
#1] and [Router #2].
That is how the Internet works. Everything is SuperNetted. It doesn't
really "break down" until it gets between the ISPs and thier customers.
There are "billions" of routes on the Internet,...there is no way every
router on the Internet can maintain all that in a routing table,...so
everything is grouped together into a fewer number of routes containing
*huge* blocks of addresses. So the router only cares about which "next hop"
router to send traffic where the destination is a member of one particular
"huge block" of addresses. Once sent it doesn't worry about it after
that,...the next decision falls on the router that received it,...and the
process repeats over and over and over.
Think about it,...an IP Segment is not supposed to get over 250-300 hosts
because performance starts to suffer from the excessive broadcasts. That is
covered by the /24 bit mask that gives 254 Hosts. So what are all the other
lower bit masks for? They are for SuperNetting upstream of the final
destination to keep routing tables small and efficient. But when it nears
the destination the IP Segments get broken down smaller and smaller until
they get down to 254 hosts or less (masks of /24 bits or higher)
--
Phillip Windell
www.wandtv.com
The views expressed, are my own and not those of my employer, or Microsoft,
or anyone else associated with me, including my cats.
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