Re: Do we use the classful address scheme yet?

In article <dlkkup$g30$1@xxxxxxxxxxxxxxxxxxxxxxx>,
roberson@xxxxxxxxxxxxxxxxxx (Walter Roberson) wrote:

> In article <1132311886.102421.282780@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
> <minseokoh@xxxxxxxxxxx> wrote:
> >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.
>
> 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.
>
> >How about the subnet concept which
> >is used with classful routing scheme.
>
> 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.

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 "192.168.10.0/24 is subnetted".

--
Barry Margolin, barmar@xxxxxxxxxxxx
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
.

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