Summarization Questions...

mattipler

Could someone please set me a couple of Summarization questions please just so I can see If I understand this properly... I think I may have got this now!

Beer tokens to whoever responds.

Cheers guys.

mikearama

You have 6 subnets, all are remote, via a single ATM router. Subnets include:

10.22.178.0 /23
10.22.180.0 /23
10.22.182.0 /23
10.22.184.0 /23
10.22.186.0 /23
10.22.188.0 /23

What summarized address can you create to deal with all that?

Oh, and locally, you use nothing after 10.22.150.0

Mike

mattipler

You have 6 subnets, all are remote, via a single ATM router. Subnets include:

10.22.178.0 /23
10.22.180.0 /23
10.22.182.0 /23
10.22.184.0 /23
10.22.186.0 /23
10.22.188.0 /23


A summarised route for the above I'd go for...

10.22.176.0 /20

My reasons (so it's easier for you to see why I've gone wrong )

/20 because the first 4 bits are the same for all address in the 3rd octet.

176 because it's a block size of 16.

Where have I gone wrong?

Oh and cheers Mike your a star mate I really appreciate this. Once I've cracked this egg I reckon that's it... I'm prepared and there's nothing I'm unsure about for next Thursdays 801!!!

Netstudent

Thats what I came up with as well. networks 178-188 gives you a block of 10 to summarize. a block of 8 is too small to include all those so your next option is 16. YOu know you need a 240 somewhere to get 1 block of 16. So 255.255.240.0

mattipler

So I got it right!?!?!?! Thank f*ck for that. Was about to drop-kick my monitor out the window.

Thanks Netstudent and Mikearama. That was the last area I was unsure of.

Netstudent

If you can do summarization like that then you should be good for the test. I don't think it gets more difficult than that.

mattipler

In that case I feel ready to roll baby!!!

networker050184

You should be good to go. Obviously you have been working hard and trying to understand all the objectives. I'm expecting a pass story and probably a high score to go along with it!

mikearama

Yeah Matt, that example is tougher than anything on the exam. The /23 is beyond anything I've seen. If you can get that one, the exam's questions should be a cake walk.

Nicely done, matt. You too, NS.

mattipler

Cheers lads for your help. Just gonna stay in this weekend... no beer, women or late nights. Just me, my laptop, my notes, my books and Boson 'pain-in-the-arse' netsim.

Hopefully I'll pass on Thursday. If I walk away with an 850 I'll be doing back-flips down the high street... well, maybe not but I'll be more than happy. On Friday I'm going to huge music festival they have each year in Britain called 'V festival'... so I'll have just-cause for celebration!

I'll let you know how I get on!

Cheers guys.

Matt

Mikdilly

mikearama wrote:

You have 6 subnets, all are remote, via a single ATM router. Subnets include:

10.22.178.0 /23
10.22.180.0 /23
10.22.182.0 /23
10.22.184.0 /23
10.22.186.0 /23
10.22.188.0 /23

What summarized address can you create to deal with all that?

Oh, and locally, you use nothing after 10.22.150.0

Mike

Is it necessary to be concerned with the prefix in the question when figuring the summary route? Wouldn't you just need to be concerned with doing the binary math to find the boundary and then use that to come up with the subnet mask for the summary route?

Netstudent

When you say prefix are you talking about the 10.22.x.x because of the subnet mask 255.255.254.0? The prefix that is the same in all of the IP's that represent a subnet will have all 1's in common so I don;t even worry about converting that to binary. I usually convert only the subnet indentifying octet to binary.

r_durant

I could be wrong, but I think he (or she) means the /23...

networker050184

You need the sumerized route to include all addresses in the range, so the /23 will tell you what addresses you need to include in the range. The binary is the most accurate way, but a little time consuming.

Mikdilly

Yes, the /23, i would think you would just be concerned wth converting the 3rd octet of each subnet number to binary so they can be matched up.

networker050184

You want it to be the smallest possible to match all addresses. If you just did the third octet you could include addresses unnecissarliy.



P.S. Had to add the new avatar its football season. GEAUX SAINTS!!!!

Mikdilly

I would get the smallest possible match which turns out to be .176 or 10110000.

mgeorge

Keep in mind that you need to know where to use summarization and where not to.

Summarization just advertises mutliple contigious subnets as 1 subnet.

But when you have multiple contigious subnets spanning across several other subnets and you use summarization this can cause problems, some networks may not be reachable.

Also keep in mind that the key to any well designed network is the documentation, nothing more, nothing less. When your in a small business remembering what routers summarize what is easy but when you get into the 100+ router networks, you have to rely on current and accurate documentation.

any who im off to work again

Netstudent

networker050184 wrote:

You want it to be the smallest possible to match all addresses. If you just did the third octet you could include addresses unnecissarliy.

So what other octets would you consider summarizing in this example? It's likely that you will include unnecesary ip's in a summarized route. Sometimes there is no perfect fit, you just have to find the tightest fit and preplan so that you don't overlap subnets.

mikearama

Netstudent wrote:

It's likely that you will include unnecesary ip's in a summarized route. Sometimes there is no perfect fit, you just have to find the tightest fit and preplan so that you don't overlap subnets.

Absolutely correct. I believe it would be rare to have a summary address that perfectly maps to all included subnets. In most cases, I think an admin/architect will create the contiguous subnets required by the 'business case', and then will summarize them as well as possible.

Don't get me wrong... all admins should plan their subnets carefully, but with expansion and new subnets being added, the best most admins can do is plan, with room to spare for expansion.

Case in point, the example I gave. It's from our own network. The senior admin stopped the local subnets at 150, and didn't start the remote subnets until 178... leaving room for both local and remote to grow.

Netstudent

Good point!

gabrielbtoledo

I don't understand the confusion.
It's simple.
1- Transform the octect that changes (in this case the third one) into binary.
2- Match the first bit that is common (from left to right).
3- Count all the bits from left to right and you will find the mask.
4- Change the binary form to decimal and you will find the summarized address.

10.22.178.0/23
1011|0010

10.22.180.0/23
1011|0100

10.22.182.0/23
1011|0110

10.22.184.0/23
1011|1000

10.22.186.0/23
1011|1010

10.22.188.0/23
1011|1100

So the fourth bit (from left to right) is the last common bit, so converting that to decimal:
10.22.176.0/20
The /20 is because first octet + second octet + 4 bits on third octet = 20 bits total

networker050184

Like Netstudent said get it as tight as possible. You could easliy use 10.22.160.0 /19 whcih would include all the addresses in your range. This would include a lot of addresses unnecisarily. Always use the binary conversion when doing this like I said before its the most accurate way.