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Supernetting Question.

Nishesh.PrasadNishesh.Prasad Member Posts: 185
in CCNA & CCENT
Hi guys, can anyone help me with the following question. I got it partly correct, but did'nt understand the Logic. Thanks.

Some time ago, your organization was allocated two Class C networks: 206.10.13.0 and
206.10.14.0. You now want to supernet these two networks so that your external router
advertises only one network on the Internet. What is the Address that will be advertised by the router ?
MCITP: EA 2008| VCP4| MCSE 2003 | CCNA | MCSA 2003: Security | MCDST | Security+ | ITILV3
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    tech-airmantech-airman Member Posts: 953
    Nishesh.Prasad wrote:
    Hi guys, can anyone help me with the following question. I got it partly correct, but did'nt understand the Logic. Thanks.

    Some time ago, your organization was allocated two Class C networks: 206.10.13.0 and
    206.10.14.0. You now want to supernet these two networks so that your external router
    advertises only one network on the Internet. What is the Address that will be advertised by the router ?

    Nishesh.Prasad,

    What is the default mask for a Class C network?
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    Nishesh.PrasadNishesh.Prasad Member Posts: 185
    255.255.255.0
    MCITP: EA 2008| VCP4| MCSE 2003 | CCNA | MCSA 2003: Security | MCDST | Security+ | ITILV3
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    tech-airmantech-airman Member Posts: 953
    Nishesh.Prasad wrote:
    255.255.255.0

    Nishesh.Prasad,

    Apply that default mask to the two previously mentioned Class C networks and what do you get?
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    Nishesh.PrasadNishesh.Prasad Member Posts: 185
    Two differrent subnets.
    MCITP: EA 2008| VCP4| MCSE 2003 | CCNA | MCSA 2003: Security | MCDST | Security+ | ITILV3
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    tech-airmantech-airman Member Posts: 953
    Nishesh.Prasad wrote:
    Two differrent subnets.

    Nishesh.Prasad,

    What are the two IP network addresses in dotted decimal format?
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    Nishesh.PrasadNishesh.Prasad Member Posts: 185
    11001110 00001010 00001101 00000000
    11001110 00001010 00001110 00000000
    MCITP: EA 2008| VCP4| MCSE 2003 | CCNA | MCSA 2003: Security | MCDST | Security+ | ITILV3
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    tech-airmantech-airman Member Posts: 953
    Nishesh.Prasad wrote:
    11001110 00001010 00001101 00000000
    11001110 00001010 00001110 00000000

    Nishesh.Prasad,

    So from left to right, how many bits are in common?
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    iwormsiworms Member Posts: 53 ■■□□□□□□□□
    Are you suggesting we use /22? But that would include 206.10.12.0 and 206.10.15.0 as well. How do we exclude those two?
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    Nishesh.PrasadNishesh.Prasad Member Posts: 185
    11001110 00001010 000011
    MCITP: EA 2008| VCP4| MCSE 2003 | CCNA | MCSA 2003: Security | MCDST | Security+ | ITILV3
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    tech-airmantech-airman Member Posts: 953
    Nishesh.Prasad wrote:
    11001110 00001010 000011

    Nishesh.Prasad,

    Convert that from binary to dotted decimal and what do you get?
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    NightShade1NightShade1 Member Posts: 433 ■■■□□□□□□□
    Nishesh.Prasad wrote:
    Hi guys, can anyone help me with the following question. I got it partly correct, but did'nt understand the Logic. Thanks.

    Some time ago, your organization was allocated two Class C networks: 206.10.13.0 and
    206.10.14.0. You now want to supernet these two networks so that your external router
    advertises only one network on the Internet. What is the Address that will be advertised by the router ?

    You cant supertnet that becuase if you try to supernet it for example a /22 you will be annoucing you have
    206.10.12.0
    206.10.15.0

    Which is not true...
    The asnwer is that you cant suppernet that...
    Partly correct? was it a question from an exam or where you got that question??
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    Nishesh.PrasadNishesh.Prasad Member Posts: 185
    NightShade1 wrote:
    Nishesh.Prasad wrote:
    Hi guys, can anyone help me with the following question. I got it partly correct, but did'nt understand the Logic. Thanks.

    Some time ago, your organization was allocated two Class C networks: 206.10.13.0 and
    206.10.14.0. You now want to supernet these two networks so that your external router
    advertises only one network on the Internet. What is the Address that will be advertised by the router ?

    You cant supertnet that becuase if you try to supernet it for example a /22 you will be annoucing you have
    206.10.12.0
    206.10.15.0

    Which is not true...
    The asnwer is that you cant suppernet that...
    Partly correct? was it a question from an exam or where you got that question??


    I know where you are going Tech-Airman .... but what NightShade has pointed out is EXACTLY what the answer is. I know 'how to' supernet. I just dont understand the logic behind the answer. This was the answer in MSPress -

    Two Class B subnets can be supernetted only if they are contiguous and the lower of the two values in the third octet is an even number. Note that this is not a “trick.” It is a real-world situation that can have serious consequences. Before the need for summarization was fully understood, Class C networks were regularly allocated that were contiguous, yet could not be summarized as a single supernet. You must know how to recognize this situation if you come across it in your professional career.


    Is there no way we can supernet the two subnets or is it that they are not contiguous in the 3rd octet which is causing the problem ? NightShade can you explain your answer in a bit more detail please ?
    MCITP: EA 2008| VCP4| MCSE 2003 | CCNA | MCSA 2003: Security | MCDST | Security+ | ITILV3
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    IgloodudeIgloodude Member Posts: 19 ■□□□□□□□□□
    If you supernet with a /23 you can have 206.10.12.0 and .13.0, or you can have a .14.0 and .15.0, but you can't combine .13.0 and .14.0 without also including the .12.0 and .15.0 (via a /22 mask), and that wouldn't be allowed because you don't own the .12 and .15.

    Does that make more sense?
    Next up: MS Server 2008 Network Infrastructure (70-642), CCNA (640-816)
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    he-manhe-man Member Posts: 49 ■■□□□□□□□□
    Im sure this thread could have been summaraized (supernetted) into much fewer post's, but it did use of some of my overwelmingly large amount of time, so for that i thank you!
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    iwormsiworms Member Posts: 53 ■■□□□□□□□□
    The complete, general-purpose answer should be, "You cannot supernet these networks into one single statement. You need two or more statements to summarize them." But since the question only has two networks to begin with, we can simply say "you cannot supernet these." If you had three or more contiguous networks, you can always partially summarize them.
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