Route Summarization

I'm trying to figure out the best route summary and mask for the routes listed below. I get 10.9.0.0 255.255.224.0. Is this correct?

10.9.9.0
10.9.13.0
10.9.15.0
10.9.16.0
10.9.17.0
10.9.18.0

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Comments

chmorin

That is what I got, but I'm out of practice.

notgoing2fail

I need to practice this more myself, I was really good at it just a couple months ago...

Hate when rust sets in....

stuh84

Yeah, either 10.9.0.0 255.255.224.0 or 10.9.0.0 255.255.255.240.0 and 10.9.16.0.0 255.255.240.0 would do it, the later ones obviously being a bit more specific, the former summarizing more.

chmorin

stuh84 wrote: »

Yeah, either 10.9.0.0 255.255.224.0 or 10.9.0.0 255.255.255.240.0 and 10.9.16.0.0 255.255.240.0 would do it, the later ones obviously being a bit more specific, the former summarizing more.

I wouldn't want to scare the kid with more supernetting hahah

notgoing2fail

stuh84 wrote: »

Yeah, either 10.9.0.0 255.255.224.0 or 10.9.0.0 255.255.255.240.0 and 10.9.16.0.0 255.255.240.0 would do it, the later ones obviously being a bit more specific, the former summarizing more.

Yes that sounds like both would work. I hadn't thought of the second one but I can see it now....

But isn't the point of summarization to get the most under one mask?

Otherwise, can't you go even further and do 255.255.248.0? LOL!!!

stuh84

Yeah it is, but it depends on the needs of the network. You may produce a summary out from one part of your network, but then need to use networks within that summary elsewhere in your network.

What I said was more of another way to think about it rather than a definitive answer in a sense.

notgoing2fail

stuh84 wrote: »

Yeah it is, but it depends on the needs of the network. You may produce a summary out from one part of your network, but then need to use networks within that summary elsewhere in your network.

What I said was more of another way to think about it rather than a definitive answer in a sense.

No I'm glad you said it, I would have never thought of it that way. The book definitley doesn't show it that way.....

If you have more examples or links I would love to read up more on this way of thinking....

alan2308

notgoing2fail wrote: »

But isn't the point of summarization to get the most under one mask?

Normally yes, but not at the risk of including too much in one summarization. If your network has some subnets elsewhere that would fall within the summary you're making, then obviously you don't want to make the one single summary. That is unless you enjoy a good routing loop.

Either way, 2 routes is still better than 6.

Edit: I really need to speed up my relpies, we got a reply and a response to the reply in the time I was typing. LOL

stuh84

notgoing2fail wrote: »

No I'm glad you said it, I would have never thought of it that way. The book definitley doesn't show it that way.....

If you have more examples or links I would love to read up more on this way of thinking....

Wait until you get into the ROUTE track on the CCNP, if its anything like BSCI, this kind of thing becomes second nature.

BSCI, or Building Scalable Cisco Internetworks, spends half the time showing that to be scalable, summarizing is important, but not to under summarize as this places constraints on hardware, but not to oversummarize, so you either blackhole traffic by going in the wrong direction, or having to have all traffic go via the one router which is doing MASSIVE summarization, defeating the purpose.

It's all quite interesting stuff

jwills

Thanks for the input. After reading these post I came up with 10.9.0.0 255.255.248.0 and 10.9.16.0 255.255.248.0 (As far as trying to advertise the minimum amount of routes)

notgoing2fail

stuh84 wrote: »

Wait until you get into the ROUTE track on the CCNP, if its anything like BSCI, this kind of thing becomes second nature.

BSCI, or Building Scalable Cisco Internetworks, spends half the time showing that to be scalable, summarizing is important, but not to under summarize as this places constraints on hardware, but not to oversummarize, so you either blackhole traffic by going in the wrong direction, or having to have all traffic go via the one router which is doing MASSIVE summarization, defeating the purpose.

It's all quite interesting stuff

oh boy!! This is why I'm doing SWITCH first because I think I can just bang it out (hopefully) and I'm going to have to spend a lot more time on ROUTE.

Route is my weakness....

Aldur

stuh84 wrote: »

Yeah, either 10.9.0.0 255.255.224.0 or 10.9.0.0 255.255.255.240.0 and 10.9.16.0.0 255.255.240.0 would do it, the later ones obviously being a bit more specific, the former summarizing more.

True that the later is more specifc but it takes two route summerizations to do it. If the question allows for two route summerizations then that'll work just fine. But from what I've seen any exam question will only want one aggregate route.

jwills wrote: »

Thanks for the input. After reading these post I came up with 10.9.0.0 255.255.248.0 and 10.9.16.0 255.255.248.0 (As far as trying to advertise the minimum amount of routes)

Those two aggregate routes will only grab 10.9.0.0 - 10.9.7.0 and 10.9.16.0 - 10.9.23.0. You're going to miss 10.9.13.0 and 10.9.15.0.