Route Summarization

Kelvin Wang

Hi, can anyone explain to me how to solve the following question? I encounter this question in the ciscopress self study book but am stuck. Your help would be much appreciated, thanks!

Your company is assigned four Class C networks:

200.39.32.0/24
200.39.33.0/24
200.39.34.0/24
200.39.35.0/24

Can these network be summarized into one route advertisement? How?

instant000

Kelvin Wang wrote: »

Hi, can anyone explain to me how to solve the following question? I encounter this question in the ciscopress self study book but am stuck. Your help would be much appreciated, thanks!

Your company is assigned four Class C networks:

200.39.32.0/24
200.39.33.0/24
200.39.34.0/24
200.39.35.0/24

Can these network be summarized into one route advertisement? How?

Yes, use a /22 mask.

Edit: I'm sorry.

Well, you need to summarize 4 contiguous networks. So, you need a mask that gives you a block size of 4.0 (or, at least, that's my initial hypothesis)
First, you check if that first number is a multiple of 4.0 or not. if not, then you'd have to go up to 8.0.
Since it is a multiple of 4, then you know you can use the mask of 255.255.252.0.
the network is 200.39.32.0
broadcast is 200.39.35.255
first valid host is 200.39.32.1
last valid host is 200.39.35.254

instant000

On another thought, to expand upon the initial answer I gave, and to look at the problem again, what if it gave you this?

200.39.33.0/24
200.39.34.0/24
200.39.35.0/24
200.39.36.0/24

And asked you to summarize it to the best of your ability, what would you do?

Well, you could take two approaches

Approach 1: give them exactly what they asked for, summarized as much as possible:
200.39.33.0/24
200.39.34.0/23
200.39.36.0/24

Approach2: If they say to use the smallest possible mask that covers all of the networks given in a single line, then you use this:
200.39.32.0/21


Problems like this illustrate why you should give out network assignments according to binary boundaries

instant000

Kelvin:

If you could show how you are attempting to solve the problem, we could then assist you. I thought route summarization was a CCNA topic?

wrwarwick

instant000 wrote: »

Kelvin:

If you could show how you are attempting to solve the problem, we could then assist you. I thought route summarization was a CCNA topic?

Route summarization is a CCNP topic, not CCNA. It is helpful to know, and is something that you should know moving forward in the networking field. Don't worry about knowing it 100% for the CCNA.

wrwarwick

wrwarwick wrote: »

Route summarization is a CCNP topic, not CCNA. It is helpful to know, and is something that you should know moving forward in the networking field. Don't worry about knowing it 100% for the CCNA.

Well, just saw this on the CCNA topics:

Determine the appropriate classless addressing scheme using VLSM and summarization to satisfy addressing requirements in a LAN/WAN environment

Kelvin Wang

instant000 wrote: »

Yes, use a /22 mask.

Edit: I'm sorry.

Well, you need to summarize 4 contiguous networks. So, you need a mask that gives you a block size of 4.0 (or, at least, that's my initial hypothesis)
First, you check if that first number is a multiple of 4.0 or not. if not, then you'd have to go up to 8.0.
Since it is a multiple of 4, then you know you can use the mask of 255.255.252.0.
the network is [URL="tel:200.39.32.0"]200.39.32.0[/URL]
broadcast is [URL="tel:200.39.35.255"]200.39.35.255[/URL]
first valid host is [URL="tel:200.39.32.1"]200.39.32.1[/URL]
last valid host is 200.39.35.254

hi Instant000, thanks for the explanation. Sorry but i have got no clue on how to attempt the qs therefore not able to provide how i attempt it. Anyway just another clarifications, the first number we talk about here is 32? Which is a multiple of 4. But i dont really get the mask, how does it link to [URL="tel:255.255.252.0"]255.255.252.0[/URL]? Is it because 252(dec) = [URL="tel:11111100"]11111100[/URL](bin) and we use the host bit 2^2 which gives 4?

Kelvin Wang

wrwarwick wrote: »

Route summarization is a CCNP topic, not CCNA. It is helpful to know, and is something that you should know moving forward in the networking field. Don't worry about knowing it 100% for the CCNA.

Thanks for the clarification sir. Yes indeed. i have passed my ccna, but somehow i am still unclear about this topic.