Do we use the classful address scheme yet?

Discussion in 'Cisco' started by minseokoh, Nov 18, 2005.

  1. minseokoh

    minseokoh Guest


    I know the CIDR (classless interdomain routing) is widely used these
    days. In the CIDR, the network ID is represented by the prefix.

    I wonder if routers today still use the classful (class A, class B,
    class C, etc.) routing scheme yet. How about the subnet concept which
    is used with classful routing scheme.

    Thank you so much.

    minseokoh, Nov 18, 2005
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  2. Yes. Some features of some routers (including Cisco) still use
    the "classful" address scheme.

    For example on the Cisco PIX, ip address pools default to classful
    addressing if you omit the subnet specification.
    It still exists even with CIDR. The subnet change introduced by
    CIDR is that the first and last induced subnet are no longer
    reserved -- e.g. in a classful scheme if you were using a 4 bit
    subnet mask then before .0 through .63 and .192 through .255 were
    reserved and only the .64-.127 and .128-.191 were usable.
    Walter Roberson, Nov 18, 2005
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  3. And Cisco router require you to configure "no ip subnet-zero" to allow
    you to use the all-0 and all-1 subnets.

    The routing table is also organized internally based on classful
    networks. So when you use "show ip route", it groups things by classful
    networks, with headings like " is subnetted".
    Barry Margolin, Nov 18, 2005
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