sivakondalarao
Let me start with the more easy one: subnet zero would be 10.0.0.1 255.255.0.0. The address that you used 10.132.0.1 is in subnet 132 not in subnet zero. If you attempt to configure 10.0.0.1 with no subnet-zero configured the router would have given an error message.
To be clear about this subnet zero is a subnet where all the bits in the subnet part of the address are zero. It may help to thing about the address being in three parts: there is the network part of the address (10. in your example), the host part of the address (0.1 in your example) and the subnet part of the address. If all the bits in the subnet part are zero then it is subnet zero.
The answer about ip classless is a bit more complicated. It is not correct to think that no ip classless will not allow you to use a classless address. The router will always allow you to configure an address (with correct subnet mask) and it is difficult to say whether an address is classful or classless. It is not really whether the address is classful or classless but how we determine subnets of the network, how we advertise it, and how we route toward it that is classful or classless.
Some people believe that ip classless or no ip classless restrict what routing protocol can be run but this is not true. IP classless does not restrict what routing protocol can be run. It is very possible to run RIPv1 (a classful protocol) with ip classless and quite possible to run OSPF (a very classless protocol) with no ip classless configured.
It helps me to thing about it in this way: we need to think about how the routing table is built and how the routing table is used to forward packets. It is the responsibility of the routing protocol to build the routing table. And ip classless or no ip classless is not involved in how the routing table is built. IP classless is used in making decisions about how to route packets not in making decisions about how to build the routing table. In particular ip classless determines whether the router will route packets toward an available supernet address.
It might help to have a small example. Assume that you have a routing table like this:
10.51.1.0 Ethernet 0
10.100.1.0 Serial 0
150.150.0.0/16 Ethernet 0
0.0.0.0/0 Serial 0
So the routing table has a couple of subnets of a network, a class B network, and a default route. So if the router gets a packet with destination 10.51.1.26 it is clear that the router will forward through Ethernet 0. If the router gets a packet with destination 150.150.2.4 it is clear that the router will forward through Ethernet 0. If the router gets a packet with destination 200.200.1.1 it is clear that the router will forward through Serial 0. What happens if the router gets a packet with destination 10.200.2.29? At this point we must determine whether the router is configured with ip classless or with no ip classless. If configured with ip classless the router will forward using the default route out Serial 0. If configured with no ip classless the router will drop the packet because with no ip classless the router will not forward toward a supernet address.
HTH
Rick
HTH
Rick
