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Summarization (question from Cisco book)

Having a hard time understanding this question from my cisco book.
Here is the diagram

http://www.streetneeds.com/uploads/misc/Drawing1.jpg
They want you to manually summarize.

1. my book first puts them in order like this

192.168.5.8/29
192.168.5.16/29  , 192.168.5.24/29
192.168.5.32/29, 192.168.5.40/29
192.168.5.56/29
Why did they put it in this order?



Why cant you put it in this order:


192.168.5.8/29
192.168.5.16/29
192.168.5.24/29
192.168.5.32/29
192.168.5.40/29
192.168.5.56/29

Thanks
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dissolved
Asked:
dissolved
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2 Solutions
 
pseudocyberCommented:
I think they're the same order.  You've just listed the subnets consecutively going down, and they've listed them going down and across (like one would read).  Perhaps it's just a matter of typesetting.

So, were you able to "supernet" them?  The CIDR details would be:

IP Address       : 192.168.5.0
Address Class    : Classless /26
Network Address  : 192.168.5.0

Subnet Address   : 192.168.5.0
Subnet Mask      : 255.255.255.192
Subnet bit mask  : nnnnnnnn.nnnnnnnn.nnnnnnnn.nnhhhhhh
Subnet Bits      : 26
Host Bits        : 6
Possible Number of Subnets : 1
Hosts per Subnet : 62


Subnet      Mask      Subnet Size      Host Range      Broadcast
192.168.5.0      255.255.255.192      62      192.168.5.1  to  192.168.5.62      192.168.5.63
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dissolvedAuthor Commented:
to be perfectly honest, I have no clue how to proceed from here.

The octet that changes is the 4th one, so I put the 4th octet in binary and try to find some matching bits.
00001000
00010000
00011000
00100000
00101000

According to above, they match in the second bit.  Am I on the right track?

Thanks
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pseudocyberCommented:
Dissolved, you're correct.  So, therefore, the mask is /26 - 24 bits from the first three octets + 2 bits from the last octet.
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dissolvedAuthor Commented:
So the route can be advertised as 192.168.5.0/26???
Will this interfere with any of the networks in the cloud on the left of Router A? Wont Router A be advertising networks that exist on both networks?  Just trying to make sense of this summarization madness. I know you know your stuff.

The answer my book says is:

>192.168.5.8/29 cannot be summarized
>192.168.5.16/29, 192.168.5.29 can be summarized as 192.168.5.16/28
>192.168.5.32/29, 192.168.5.40/29 can be summarized as 192.168.5.32/28
>192.168.5.56 cannot be summarized

I'm assuming they are summarizing multiple routes because some of the networks on the left of Router A may get confused?

(damn, now I'm confused lol)
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pseudocyberCommented:
Oh, yeah, you're absolutely right.  Kind of hard from your post and just the drawing.  Router A can't summarize the whole thing, because the summarization would include nets to the left, or "above" the summary point.    5.56 can't be summarized without including nets to the left of Router A.

You're understanding it perfectly, it seems. :)
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dissolvedAuthor Commented:
Thanks for the confirmation. So that is why they listed the networks like this
192.168.5.8/29
192.168.5.16/29  , 192.168.5.24/29
192.168.5.32/29, 192.168.5.40/29
192.168.5.56/29

as opposed to listing them just all veritically?  How would one tell (when performing manual summarization) what will interfere with other networks.
Thanks
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pseudocyberCommented:
You have to manually figure out the networks which fall inside your summarization.  If you understand subnetting, you can simply reverse the process to get the subnets inside the summarization.

For instance, say you want to summarize

192.168.1.0, 192.168.1.64, 192.168.1.128, and 192.168.1.192.  All /25

You could go through your supernetting (CIDR) procedure in binary and see that the answer is 192.168.1.0/24.  Then, you want to know which networks are included or not.  Well, simply reverse the procedure and take your 192.168.1.0/24 net and subnet it into 4 subnets ...

Or, with your supernet, figure out the host addresses - figure out they start with .1 (assuming a .0 net) and they end with what - say a .254.  And the broadcast is .255.  So, you know if your hosts are from 192.168.1.1 to 192.168.1.254 then any subnet which falls within this range is going to be included in the supernet.
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pseudocyberCommented:
Sorry, those subnets should have been /26, not /25.
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pseudocyberCommented:
A better summary example would have been to summarize TWO of them, and not the other two.  So, if you create a 192.168.1.128/26 supernet - then you could have seen that what is included is 192.168.1.128/25 and 192.168.1.192/25 but NOT 192.168.1.0 or 192.168.1.64.
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PennGwynCommented:
As a first step, I write down all the /29 blocks in order, as you did.

As a second step, I look for pairs of adjacent /29 blocks where:
  a) The first block is on a /28 boundary, and
  b) Both blocks are out the same router interface
These can be grouped on the same line, as the book lists them, and then summarized as /28 blocks.

If there are suitable adjacent /28 blocks (same conditions), they can be summarized as /27 blocks, and so on.

Carefully note conditions a) and b).  Sometimes only one condition or the other is met, but you need both for summarization to work.

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