Somebody said that I summarized 128 subnets and not 100 subnets, how do they know? As a matter of fact, I did summarize 100 subnets although the answer can be true for more or even less subnets. They are just trying to complicate things and confuse people that are trying to learn.
The Dude
Look at your answer! Tell me what networks are included.
Doan
On Tue, 1 Aug 2006, it was written:
I think you have no clue about subnets. Summarizing certain subnets means to come up with one IP address only!
The Dude
So why not 0.0.0.0/0?
Doan
On Tue, 1 Aug 2006, it was written:
Looking at your question I take back what I said earlier. Let me correct it: " You have no clue about IP addresses!
Hihihi! So please enlighten me with your superior knowledge, master!
Doan
On Tue, 1 Aug 2006, it was written:
to the dude, you've got a point that summarization as i've seen it means 1 IP address. And I think that usually they all oversummarize. So I dont have a problem with your summarisation of 10/9. I'd even say I agree with your answer.
If the question said "make a bunch of route summaries such that they don't oversummarize, then looking at john's question. john's solution- which is a correction of doan's answer (doan didn't quite nail it) makes sense to me. But it could be that cisco give 2 types of answer. The Cisco Press CCNA book i've got , from memory, always gives 1 IP address. But the original poster's CCNP flash cards (cisco press?) gives more than one IP address.
Now, "the dude" I sympathise with your frustration, and I don't disagree with your language, and I think being argumentative as you are, and emphasising disagreement, is the way forward in finding answers. It's rare and refreshing to see it.
But let me tell you that you have done 2 wrong things. I hope it's ignorance and i'm sure it's not intentional clown like behaviour
I suggest you go to
If you could post through the archive, then you'd post in the correct places, and the whole thread would be easy to follow. And you'd find peoples' posts. Instead, you post here there and everywhere and top post.
If you didn't know about that, then it's forgiveable. I'm suprised nobody pointed this out.
If you are as you appear to me, then i'm sure you'll appreciate being corrected.
Maybe then you'll get mad at people that make their posts disappear from google's archive!!!
If i'm correct in my judgement, it appears that you come from a similar planet to me.
Er, it depends. Often just the blamket summary is OK, but normally for excercises, exact summarisation is what is wanted.
eg to summarise 0 - 100 in practice a .128 mask will do, but it will include
101 - 127 as well. That may or my not be an issue. As an excercise, what id probably wanted is the exact summarisation, even if it takes a few entries, as that will be fewer entries in a routing table.
v useful, thanks
v useful, thanks
Well, hang in there buddy. You'll get the grasp of it soon enough.....
There is no "single" summarization statement that will summarize 0 through
100. The /9 mask summarized 0-127. It is a bad thing to advertise network space that you don't have. So, there were three statements required to summarize "only" that network space. No one was trying to fool/trick/confuse you. This is just part of the learning experience, that's all.Keep plugging along.... You'll get there.
Thanks for your time and patience, you seem to be a really nice guy and totally understanding. Sometimes, I just like to joke around. I do appreciate your help though!
The Dude
Someone just pointed out that top posting is not a good thing ...
Anyway, where did you get that 128 number, by the way?
I summarized by comparing (in my mind) all given IP addresses and found out that only the 9 leftmost bits were common. Just followed CISCO guidelines on summarization. Every other answer is to trick/confuse people. This is my story and I will stick to it!
The Dude
you are top posting. that's bad.
A: Because it interrupts the flow of conversation. Q: Why is top posting annoying? A: Top posting. Q: What is the most annoying thing on Usenet?
My cisco press ccna book uses the one ip address that oversummarizes (i.e. like "the dude"). (there were no examples of a discontiguous address space to summarize or a corresponding discontiguous summarization, but there was still oversummarization).
But based on what john said, in real life, you wouldn't oversummarize. also, those CCNP (cisco press?) flash cards had a few summarizations(like real life).
go by cisco press for cisco exams. for CCNA, do 1 summarization. Real life appears to be different. I don't yet know about CCNP(cisco press).
incase i'm wrong about cisco press CCNA, do check yourselves and report back. But that is my memory of cisco press CCNA. I certainly recall them having pictures of subnetworks and givign one summarization and saying it's a tradeoff. (I guess between number of summarizations and oversummarization).
To begin with, I find the question very stupid...
A similar question was given to students by a math teacher who wanted to spend some time with his fiancee ... He asked students to add numbers from 1 to 100. A bright student, The Dude, no I am kidding, that bright student was GAUS, lined up in his mind:
1, 2, ... , 49, 50 100, 99, ...., 52, 51Then he thought: 101 x 50 = 5050
Gaus found the answer in a few seconds and the math teacher was so mad, the same way, some folks are mad here at my answer. Probably they asked this stupid question thinking that we would waste our time lining up in binaries
101 IP addresses ...The Dude
Actually, their answers were correct too. The CCNA answer of 1 summarization statement, may be a dumbed down simplification. You know, I once spoke to somebody that was studying for an MCSE exam , he pointed to the printer, and said "that is not a printer", "it's a printing device". "The printer is this icon over here". The CCNA may not have anything as stupid as that, but sometimes what is true in the real world, trumps what is true in an exam. And you should know Both, what is true for the exam, and that the exam is wrong/stupid, and what is true in the real world.
I think there can be 2 problems with usenet people
But generally, I think people in this thread haven't been so bad. You respodned strongly to Doan, but Doan wasn't bad. Consider that when Doan gave his answer with many summarization statements, and you disagreed, neither of you gave references. Elsewhere in the thread, Doan gave an answer to the original question, with 1 summariation statement. And he also identified a good answer (ern's) to the orignial one. So, he contributed a lot. The people, like John(CCIE) and Doan and others that gave many summarizations and explanations, were not malicious. It's good to have many explanations. And their answers were correct too - for the real world apparently. So it's important to see those answers. All correct explanations are good. If you think that an explanation is poor, and you understand it, then it means you really understand the topic! We have books. It doesn't matter if you think people on usenet give difficult explanations. And considering the answers of many route summarizations, those explanations were fine. The important thing is that a)the explanations are correct (so don't contain wrong information) b)misconceptions are cleared up (books often don't clear up misconceptions).
nonsense must be identified as nonsense! but preferably each side should give references - if they each maintain their positions. Otherwise it's not useful.
You shouldn't write it in quotes. It's a standard phrase
top posting applies to what is within a post. Not the order of posts within a thread. you are writing like in a typical email. You are writing your response at the start of the post, and quoting the person below. It should be the other way around. Quote the person and then respond to him below that. In the manner that I am responding to you. Were you to google "top posting" you would get a long list of transgressors along with explanations.
I found this illustration of top posting via googling usenet for "top posting" A: Because it interrupts the flow of conversation. Q: Why is top posting annoying? A: Top posting. Q: What is the most annoying thing on Usenet?
You see how discussion is possible by quoting a person and interspersing your comments within what they have written, and snipping () accordingly. There are examples of this all over usenet.
Top posting doesn't bother me.
Look ! I am "middle posting!"
As all of us humans on planet Earth know, exams and the 'real' world are two different things.
Here is a good rule for summarization that applies in the real world, and may or may not apply to what cisco wants as an answer on an exam question...
It is never a good idea to include networks that you do not have an explicit route for in a summarization statement. When advertising "reach-a-bility," one should advertise only networks/subnets that one indeed has a route for. Advertising routes that one does not have an explicit route for can lead to ambiguous routing information, and problems in a real network.
That being said, here is "my" rule for summarizing:
ALL of the bits to the left of the mask boundary must be indentical. (you have that down already) The "summarizer" must own / have an explicit route for EVERY combination of bits to the right of the adjusted boundary.
Therefore:
10.0.0.0 /9includes all this space: (second octet only is being shown)
0xxxxxxxTHAT includes:
00000000 = 0 thru 01111111 = 127 (did I say 128 in the previous ? Sorry.)If I wanted to summarize 0 through 100, I would have to use a mask greater than /9, otherwise I would be claiming reach-a-bility for space I don't have.
That is why we saw in Doan's solution 3 seperate summarization statements.
10.0.0.0 /9 included 10.0.0.0 thru 10.63.0.0 ( a large 'block')10.64.0.0 /10 included 10.64.0.0 thru 10.95.0.0 (a smaller 'block')
10.96.0.0 /14 included 10.96.0.0 thru 10.99.0.0 (a pretty whimpy block)10.100.0.0 /16 included the left-over / stragler route, and was sent as is.
By using these three summarization statements, you are advertising ONLY what you can reach / are aware of.
That is the way to do it in the "real" world.
I hope you undertsnad what I am saying, and I hope that any "test" question you may happen to have is worded in such as way as to be unambiguous with respect to the answer the test creator is searching for. I also hope that the choices of answers are also legit.
I have discovered that when using 'practice' tests from (for profit) companies like Boson, Testking, etc, there is much to be desired in both categories.
The 'real' tests are a notch better, but - still not perfect.
So hang in there, do your best, and you will pass. Trust in the force. Don't be too worried about what you may 'think' the test writer guy 'wants.' You'll get there.
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