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
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.
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".
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