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Hi,

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.

Min

In article < .com>,
<> 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.
--
Chocolate is "more than a food but less than a drug" -- RJ Huxtable

In article <dlkkup$g30$>,
(Walter Roberson) wrote:

> In article < .com>,
> <> 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,
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***