Summarization help

Can someone explain to me exactly how you get to these answers from this question? Its a question from my Cisco Press CCNP flash cards.

What is the best summarization for:

10.0.152.0/21 10.0.160.0/21 10.0.168.0/21 10.0.176.0/21 10.0.184.0/22 10.0.188.0/22

I know the answers are 10.0.152.0/21 and 10.0.160.0/19, but I am a bit confused as to how you work out the problem to find these solutions, especially for the 10.0.160.0/19. Any help is appreciated.

Reply to
Michael
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Just do it in binary.

10.0.152.0/21 = 10.0.128+0+0 +0 +16 (+8+0+0.0) 10.0.160.0/21 = 10.0.128+0+32+0 +0 10.0.168.0/21 = 10.0.128+0+32+0 +8 10.0.176.0/21 = 10.0.128+0+32+16+0 10.0.184.0/22 = 10.0.128+0+32+16+8+0 10.0.188.0/22 = 10.0.128+0+32+16+8+4

common bits are 10.0.128+0. Therefor the answer is 10.0.128.0/18

Doan

Reply to
Doan

Which naturally does not correspond to any of the answers he said were in the flash book. How do you get the 18?

Reply to
A Sharp

Write down the third octet in binairy for each IP-address and but them in a list:

10011000 10100000 10101000 10110000 10111000 10111100

They all differ, accept the last two numbers. The last two numbers are always 00. Put a line in this:

100110|00 101000|00 101010|00 101100|00 101110|00 101111|00

Now you can see that you're summerisation is 10.0.152.0/22.. I don't see how you get 10.0.152/21 and 10.0.160.0/19...

"Michael" schreef in bericht news:ku_hg.15803$ snipped-for-privacy@tornado.southeast.rr.com...

Reply to
CCNA Nerd

And this thread just gets more confusing, doesn't it? Now we have four right answers.

Reply to
A Sharp

This confermes my opinion:

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"A Sharp" schreef in bericht news:sq8ig.7658$ snipped-for-privacy@tornado.tampabay.rr.com...

Reply to
CCNA Nerd

I believe the book is wrong. It is better to understand the concept than blindly believe in the book. The /18 comes from 8+8+2 (8 in the first octet, 8 in the second octet and 2 in the third octet).

Doan

Reply to
Doan

Aren't you suppose to look at the common bits from left to right?

Doan

Reply to
Doan

"For summarization to work properly, addresses must be carefully assigned in a hierarchical fashion so that summarized addresses share the same high-order bits."

High-order bits are on the left, not right.

Doan

Reply to
Doan

Michael napisa=B3(a):

It's simple ;)

First - let's write down network ranges:

1 10.0.152.0/21 10.0.152.0 - 10.0.159.255 2 10.0.160.0/21 10.0.160.0 - 10.0.167.255 3 10.0.168.0/21 10.0.168.0 - 10.0.175.255 4 10.0.176.0/21 10.0.176.0 - 10.0.183.255 5 10.0.184.0/22 10.0.184.0 - 10.0.187.255 6 10.0.188.0/22 10.0.188.0 - 10.0.191.255

2,3,4,5 and 6 can be summarized to 10.0.160.0/19 range: 10.0.160.0 -=20

10.0.191.255 (the same)

all these networks can be summarized to 10.0.128.0/18 range:=20

10.0.128.0 - 10.0.191.255 but the question is tricky. We have only those network and nothing else - especially networks=20 10.0.128.0 to 10.0.151.0 can be somwhere else.

So the aswer in the flash cards is OK

------------------------ Ern

Reply to
Ern

How do you guys do this quickly ?

Ern wrote:

Reply to
genki

Thanks, Ern. That is the best explanation!

Doan

Reply to
Doan

I have found the best way is also to write in binary but some of our colleagues have made this somewhat harder than it has to be.

First, convert the 3rd octects into binary:

10011000 10100000 10101000 10101100 10111000 10111100

Then draw a line (starting from the left not the right!) of all matching bits:

10011000 (this network is the oddball, so it's its own network, hence answer 10.0.152.0/21

The 2nd summariztion is:

101|00000 101|01000 101|01100 101|11000 101|11100

Now you can see how the first 3 bits match which gives you

10.0.160.0/19.

Hope this helps!

Reply to
anthropomorphicon

I don't know whether to LOL or . We now have at least three different answers in this one thread.

Reply to
A Sharp

laugh at yourself. 'cos the answer written in the first post by the original poster has been explained many times now. It's the same answer. so I don't see what you're complaining about.

Reply to
q_q_anonymous

I'm not compla "Just do it in binary.

10.0.152.0/21 = 10.0.128+0+0 +0 +16 (+8+0+0.0) 10.0.160.0/21 = 10.0.128+0+32+0 +0 10.0.168.0/21 = 10.0.128+0+32+0 +8 10.0.176.0/21 = 10.0.128+0+32+16+0 10.0.184.0/22 = 10.0.128+0+32+16+8+0 10.0.188.0/22 = 10.0.128+0+32+16+8+4

comm "Write down the third octet in binairy for each IP-address and but them in a list:

10011000 10100000 10101000 10110000 10111000 10111100

They all differ, accept the last two numbers. The last two numbers are always 00. Put a line in this:

100110|00 101000|00 101010|00 101100|00 101110|00 101111|00

Now you can see that you're summerisati "It's simple ;)

First - let's write down network ranges:

1 10.0.152.0/21 10.0.152.0 - 10.0.159.255 2 10.0.160.0/21 10.0.160.0 - 10.0.167.255 3 10.0.168.0/21 10.0.168.0 - 10.0.175.255 4 10.0.176.0/21 10.0.176.0 - 10.0.183.255 5 10.0.184.0/22 10.0.184.0 - 10.0.187.255 6 10.0.188.0/22 10.0.188.0 - 10.0.191.255

2,3,4,5 and 6 can be summarized to 10.0.160.0/19 range: 10.0.160.0 -

10.0.191.255 (the same)

all these networks can be summarized to 10.0.128.0/18 range:

10.0.128.0 - 10.0.191.255 but the question is tricky. We have only those network and nothing else - especially networks 10.0.128.0 to 10.0.151.0 can be somwhere else.

So the aswer in the flash cards is OK"

So what I am suggesting is that this appears to be a tricky question, as noted by Ern, and the answer from the uninitiated reading this thread may not be completely clear.

Reply to
A Sharp

and as noted, it's better to see all ways of answering a question, and it also gave confirmation as to what the correct answers are.

  • how one could slip up.

You understand it. Yet you say it's too complicated.

Don't try to dumb things down. Let ppl gain a higher level of understanding.

Reply to
q_q_anonymous

Sorry, I haven't followed this thread and, as I use outlook express, cannot read the original post. What was the question again?

new guy :)

Reply to
new guy

new guy napisa=B3(a):

use google :)

it took me less than 1 minute to find it

--=20

------------------------ Ern

Reply to
Ern

The question was:

Can someone explain to me exactly how you get to these answers from this question? Its a question from my Cisco Press CCNP flash cards.

What is the best summarization for:

10.0.152.0/21 10.0.160.0/21 10.0.168.0/21 10.0.176.0/21 10.0.184.0/22 10.0.188.0/22

I know the answers are 10.0.152.0/21 and 10.0.160.0/19, but I am a bit confused as to how you work out the problem to find these solutions, especially for the 10.0.160.0/19. Any help is appreciated.

"new guy" schreef in bericht news:4czjg.19488$IK3.8477@pd7tw1no...

Reply to
CCNA Nerd

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