Route summarization

jtdk985

Hey all,

I'm having a rough time going through these practice labs in Todd Lammles book regarding route summarization.

I looked up a good blog regarding it, but just want some feedback if anyone knows an easier, faster way, and one that is full proof regarding all types of problems with route summarization, and a good step by step process to follow.

here are the problems and answers:

It says determine the summary address and the mask to be used that will summarize the subnets.

Q: 192.168.1.0/24 through 192.168.12.0/24
A: 192.168.0.0/20

Q: 203.168.6.0/24 and 203.168.60.0/24
A: 192.168.96.0 255.255.240.0

Q: 66.66.0.0 through 66.66.15.0
A: 66.66.0.0/16

If anyone can help me understand these will a good step by step process, I think i can have this down perfect. They just throw me off for some reason...

THANKS!

CodeBlox

Take this one for example:

Q: 192.168.1.0/24 through 192.168.12.0/24

192.168.0.0/20

You'll want to first determine your "multiplier" also known as a "block size" to summarize. This is how I do it. Get the highest value network first(in this case it's 192.168.12.0.

To get your multiplier, know that it is the place value of the least significant subnet bit. you'll want the multiplier to be just higher than your greatest network so it has to at least be greater than 12.

Here is how to get the multiplier.

11111111 11111111 11110000 00000000


That place value is 16.

And since this takes place in the third octet, and that you need a multipler of at least 16 that your mask could be /20

The summary 192.168.0.0 /20 would summarize everything from:

192.168.0.0 - 192.168.15.255

I hope i didn't complicate things.

jtdk985

CodeBlox wrote: »

Take this one for example:

192.168.0.0/20

You'll want to first determine your "multiplier" also known as a "block size" to summarize. This is how I do it. Get the highest value network first(in this case it's 192.168.12.0.

To get your multiplier, know that it is the place value of the least significant subnet bit. you'll want the multiplier to be just higher than your greatest network so it has to at least be greater than 12.

Here is how to get the multiplier.

11111111 11111111 11110000 00000000


That place value is 16.

And since this takes place in the third octet, and that you need a multipler of at least 16 that your mask could be /20

The summary 192.168.0.0 /20 would summarize everything from:

192.168.0.0 - 192.168.15.255

I hope i didn't complicate things.

Nope, thank you! that was actually one of the easier ones

Can you apply that to the other 2 and explain it out for me?

CodeBlox

Take this one:


203.168.6.0/24 and 203.168.60.0/24


You want to summarize these two networks. The highest is 203.168.60.0 /24 and you'll want the summary to include both bounds. The lowest is 203.168.6.0 and the highest being 203.168.60.0.

You know you need a multiplier of at least 64 and this is going to be in the third octet. You need two subnet bits for this and the place value of the least significant would be 64

11111111 11111111 11000000 00000000

Your mask should be /18 which would yield a multiplier of 64

The summary 203.168.0.0 /18 would summarize:

203.168.0.0 - 203.168.63.255 /18


If a network falls in that range it's a part of this summary.

As far as the multiplier(block size) goes, the place values would be:

128 64 32 16 8 4 2 1

I chose 64 because it's the place value of the least significant subnet bit in the third octet:

11000000

jtdk985

CodeBlox wrote: »

Take this one:


203.168.6.0/24 and 203.168.60.0/24


You want to summarize these two networks. The highest is 203.168.60.0 /24 and you'll want the summary to include both bounds. The lowest is 203.168.6.0 and the highest being 203.168.60.0.

You know you need a multiplier of at least 64 and this is going to be in the third octet. You need two subnet bits for this and the place value of the least significant would be 64

11111111 11111111 11000000 00000000

Your mask should be /18 which would yield a multiplier of 64

The summary 203.168.0.0 /18 would summarize:

203.168.0.0 - 203.168.63.255 /18


If a network falls in that range it's a part of this summary.

As far as the multiplier(block size) goes, the place values would be:

128 64 32 16 8 4 2 1

I chose 64 because it's the place value of the least significant subnet bit in the third octet:

11000000

so am i completely wrong in what the books answer gives? if you look at my OP, under the question is the books answer.. and im going nuts trying to see how they got that, well.. how and WHY

Thanks for more replies!

CodeBlox

Are you asking if this is the correct answer to this question:

Q: 203.168.6.0/24 and 203.168.60.0/24
A: 192.168.96.0 255.255.240.0

???

jtdk985

CodeBlox wrote: »

Are you asking if this is the correct answer to this question:



???

no, thats the correct answer the book gives.

CodeBlox

Q: 203.168.6.0/24 and 203.168.60.0/24
A: 192.168.96.0 255.255.240.0

192.168.96.0 /20 is not the summary route -_- That should be incorrect.

It could be 203.168.0.0 /18 like i have said.

jtdk985

CodeBlox wrote: »

Q: 203.168.6.0/24 and 203.168.60.0/24
A: 192.168.96.0 255.255.240.0

192.168.96.0 /20 is not the summary route -_- That should be incorrect.

It could be 203.168.0.0 /18 like i have said.

haha, ive been trying to figure that one out i knew it wasnt THAT complicated.. alright thank you for your posts. i think i can get through this

CodeBlox

Todd Lammle's book eh? I used the cisco press books. Last of Todd's books I read was for Network+ and the book had so many errors.

CodeBlox

Q: 203.168.6.0/24 and 203.168.60.0/24
A: 192.168.96.0 255.255.240.0

Just thought that I should mention, a good sanity check to verify would be to write all subnets out in binary and copy each set of bits from each that are the same. When there is a difference in bit pattern, you stop. I will show you what I mean with the 203.168.6.0 and 203.168.60 networks

203.168.6.0 = 11001011.10101000.00000110.00000000
203.168.60.0 = 11001011.10101000.00111100.00000000


If you line them up like so:

11001011.10101000.00000110.00000000
11001011.10101000.00111100.00000000

The bits in red are all the same. This gives you your mask as well as your summary route. 18 bits are the same so it's a /18

And if you translate 11001011.10101000.00000000.00000000 to decimal you get 203.168.0.0 /18

it's a sure fire way to know you're correct.

jwashington1981

jtdk985 wrote: »

Q: 66.66.0.0 through 66.66.15.0
A: 66.66.0.0/16

Something about that doesn't seem right. You should be able to summarize that with something smaller such as a /20. Considering that the octet of interest is the third octet and 0-15 creates a block of 16, a /20 would seem to be the most correct answer. A /16 would still work but it would summarize more than just what is actually asked. It would summarize 66.66.0.0 through 66.66.255.0.

CodeBlox

jwashington1981 wrote: »

Something about that doesn't seem right. You should be able to summarize that with something smaller such as a /20. Considering that the octet of interest is the third octet and 0-15 creates a block of 16, a /20 would seem to be the most correct answer. A /16 would still work but it would summarize more than just what is actually asked. It would summarize 66.66.0.0 through 66.66.255.0.

We can't really say as there was no prefix length (subnet mask) provided with the said subnets. That's given VLSMs are used.

jwashington1981

I think it would be safe to assume that not knowing the /prefix wouldn't affect this one example as Todd Lammle does that a few times in his CCNA study guide.

I'll give you one of the examples from his book and give the answer he gives.

192.168.16.0 through network 192.168.31.0
His answer: 192.168.16.0/20

Technically, you could do the same thing and say 192.168.0.0/16 since the prefix lengths aren't given and the only two octets similar are the first two octets.

The way I explained why you would use a /20 in jtdk985's question and the answer I gave from Todd Lammle's example from his study guide are exactly the same so I'm not sure why that /16 was used in the first place.

jwashington1981

Jtdk, that 985 in your name, is that an area code?

jtdk985

jwashington1981 wrote: »

Jtdk, that 985 in your name, is that an area code?

nope just random letters/numbers

jtdk985

hey all,

question:

/8 is 255.0.0.0

/16 is 255.255.0.0

/24 is 255.255.255.0

when im subnetting or doing route summarization, and i get a default mask, what does it count up by? specifically for summarization i guess. my mind is stuck on something that i need to pry out of place, so i can just say... "ooooohhhh, you im stupid".

so with this question:

Q: 172.148.0.0/13 through 172.156.0.0/13

A (given by book): 172.144.0.0/16

now thats a default mask, and going on that answer, its counting up by 1 each time?

so 144, 145, 146, etc?

i think im just confusing myself each time.. or the book is just way off

Chris_

The book is way off! The answer should be with a /12 - now see if that makes sense to you.

Chris_

....and as far as I can see, the subnets in the question aren't valid networks for a /13!!!

jtdk985

Chris_ wrote: »

The book is way off! The answer should be with a /12 - now see if that makes sense to you.

chris do you mind a quick explanation?

if you write it out in binary:

10101100.10010100 172.148
10101100.10010101 172.149
10101100.10010110 172.150
10101100.10010111 172.151
10101100.10011000 172.152

damn.. i messed myself up by skipping things

does anyone know a full proof fast method? i was trying to use http://subnettingmadeeasy.blogspot.com/2007/11/router-summarization.html but it doesnt seem to work well with this example, unless im applying it wrong?

jtdk985

yes by really writing it out a /12 works, but will it always be this simple? and im looking for a speedy way that is always %100 reliable

techie2012

CodeBlox wrote: »

Q: 203.168.6.0/24 and 203.168.60.0/24
A: 192.168.96.0 255.255.240.0

192.168.96.0 /20 is not the summary route -_- That should be incorrect.

It could be 203.168.0.0 /18 like i have said.

I remember reading that part in the summarization section of the chapter and going : but figured it was an error and moved on. Good for me haha

CodeBlox

jtdk985 wrote: »

hey all,

question:

/8 is 255.0.0.0

/16 is 255.255.0.0

/24 is 255.255.255.0

when im subnetting or doing route summarization, and i get a default mask, what does it count up by? specifically for summarization i guess. my mind is stuck on something that i need to pry out of place, so i can just say... "ooooohhhh, you im stupid".

so with this question:

Q: 172.148.0.0/13 through 172.156.0.0/13

A (given by book): 172.144.0.0/16

now thats a default mask, and going on that answer, its counting up by 1 each time?

so 144, 145, 146, etc?

i think im just confusing myself each time.. or the book is just way off

As someone else said you could use a 172.144.0.0 /12

Your summary would include addresses from:

172.144.0.0 - 172.159.255.255

If you use a /13 the summary would only be:

172.144.0.0 - 172.152.255.255