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Variable Length Subnet Masking....

Discussion in 'Technology' started by Phil Mitchell, May 11, 2006.

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  1. Phil Mitchell

    Phil Mitchell check me a dollar brer?

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    Variable Length Subnet Masking....

    anyone know anything about this???

    Why would you need to use it in the following setup?


    Site B--------|60hosts
    |
    |
    |
    Site A------- A1|-----30 hosts
    | B1|------500hosts
    |
    |
    |
    Site C--------|240Hosts


    (hosts listed are maximum number of hosts) and Site A1 Subnet is the management network
    Phil Mitchell, May 11, 2006
    #1
  2. 1615634792921.png
  3. ManofScience

    ManofScience Guest

    isn't it because u can only use 256 (0 > 255) addresses unless u shift the mask?
    ManofScience, May 11, 2006
    #2
  4. Phil Mitchell

    Phil Mitchell check me a dollar brer?

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    Dunno you tell me :lol:
    Phil Mitchell, May 11, 2006
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  5. French William

    French William _________________

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    We're gonna need a 'Simon's Homework Forum' before long.
    French William, May 11, 2006
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  6. Conway

    Conway helmet Staff

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    Re: Variable Length Subnet Masking....

    You would use it so you're making efficient use of your IP pool.

    read this ;)
    Conway, May 11, 2006
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  7. Phil Mitchell

    Phil Mitchell check me a dollar brer?

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    Re: Re: Variable Length Subnet Masking....

    Ive been reading that exact page for about 2 hours now and still cant justify the choice :cry:
    Phil Mitchell, May 11, 2006
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  8. theridler

    theridler Registered User

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    I'm currently doing a cisco course mate and have done VLSM.

    Is that all there is to the question?

    What is the ip address?
    theridler, May 11, 2006
    #7
  9. Conway

    Conway helmet Staff

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    It's dead simple....

    You can't put all of those together in one class C because you don't have enough in one (253 if you're going by RFC 1519 i think it is) and you have a total of 830 required hosts there.

    Putting it all into a class B is possible but it would leave a huge amount of wasted IP addresses that you'll never use, so the best solution is to use VLSM to specify subnets for each section of the network.

    It means you are making efficient use of your IP resources and not wasting an entire class B network segment, in addition it means you could add other sections onto the network fairly easily using the same method.

    Make sense?
    Conway, May 11, 2006
    #8
  10. theridler

    theridler Registered User

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    Is it a class C ip address?
    theridler, May 11, 2006
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  11. trance_fan

    trance_fan Registered User

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    Listen up newbies.

    Normal subnet masking can be very wasteful, say you subnet a network...eg 192.168.1.0 with a /27 mask (255.255.255.224). This gives us 8 subnets (assuming ip subnet zero is on, otherwise its 6) and 30 usable hosts per subnet.

    so within our 8 subnets, there may be a subnet that only has a point to point link, using 2 addresses, wasting 28. Instead, these point to point could use a /30 mask (255.255.255.252) that only allows 2 usable hosts per subnet - and therefore doesnt waste the space.

    VLSM was introduced to aid the IP shortage and make more efficient use of IP address space.

    You would need to use it in that setup...basically because the minimum is 60 hosts, and the maximum is 500! So you would be wasting at least 1170 addresses if you were to implement a flat scheme, and thats just over those 4 subnets!

    To subnet a network where 500 hosts per subnet is needed (therefore its gona be a class B address such as 172.16.0.0) you would need a netmask of 255.255.254.0 (/23)

    This allows for 128 subnets with 510 hosts per subnet. You would only be using 4 of those 128 subnets, so think of that wastage overall!! (its 12240 addresses!)

    Subnet 1 range would be 172.16.0.1 - 172.16.1.254

    and so on and so forth.

    Thats why!
    trance_fan, May 11, 2006
    #10
  12. Phil Mitchell

    Phil Mitchell check me a dollar brer?

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    its a Class A address

    10.27.128.0/20
    Phil Mitchell, May 11, 2006
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  13. theridler

    theridler Registered User

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    Then the answer to your question is millions of host addresses would be wasted if VLSM was not used. :up:
    theridler, May 11, 2006
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  14. Jambon

    Jambon Jambons Disco Club

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    networking was so boring.

    proper virgins unit.

    wtach as geeks like uk get hard over a subnet mask.
    Jambon, May 12, 2006
    #13
  15. Alexander

    Alexander Registered User

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    :lol: :lol:
    Alexander, May 12, 2006
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  16. trance_fan

    trance_fan Registered User

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    same crack as above with many many more wasted addresses!
    trance_fan, May 12, 2006
    #15
  17. trance_fan

    trance_fan Registered User

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    :lol: :down:
    trance_fan, May 12, 2006
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  18. Jambon

    Jambon Jambons Disco Club

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    HAVE YOU EVER SEEN A MINGE. :lol:
    Jambon, May 12, 2006
    #17
  19. trance_fan

    trance_fan Registered User

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    many!
    trance_fan, May 12, 2006
    #18
  20. theridler

    theridler Registered User

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    that aimed at me Jambum?
    theridler, May 12, 2006
    #19
  21. trance_fan

    trance_fan Registered User

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    I'd say it was more aimed at me to be fair :lol:
    trance_fan, May 12, 2006
    #20
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