Re: subnetting C class into /26 /25 /26, why can this be done?

From: Olivier Nicole (on_at_cs.ait.ac.th)
Date: 08/28/03

  • Next message: hilman firmansyah: "Re: Gif IPTunnel networkA-to-networkB not work" 
    Date: Thu, 28 Aug 2003 09:45:09 +0700 (ICT)
To: freebsd-net@freebsd.org

    Christoffer Pio wrote:
    > Is it not possible to subnet a C class into 3 nets, like
    >
    > 0-63
    > 64-191 <-- Offending network (?)
    > 192-255
    >
    > If so, why is this?

    I think you got explanations on the why.

    Now it should still be possible to subnet the way you want I think.

    While I would never recommend it, think routing should go with the
    most significant mask for a given address.

    So if you subnet:

    1) x.x.x.0/26
    2) x.x.x.192/26
    3) x.x.x.0/24

    you should be able to do the trick.

    An address in the range 0-63 will match both mask 1) and 3) but mask
    1) is most significant (more bits, higer value) so the packet will be
    routed to subnet 1).

    Same thing for a packet in the range 192-255, with subnet 2) and 3),
    it will be router to subnet 2).

    And a packet in the range 64-191 will only match the subnet 3) so it
    will go to the subnet 3).

    IF I AM NOT WRONG, this should work, but it is definitely nasty.

    If you absolutely need 2 subnets of 64 addresses and one of 128,
    doing:

    1) x.x.x.0/26
    2) x.x.x.64/26
    3) x.x.x.128/25

    is nicer and will result in the ranges 0-64, 64-127 and 128-255.

    Olivier
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  • Next message: hilman firmansyah: "Re: Gif IPTunnel networkA-to-networkB not work"

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