1.IP zero subnet (ip subnet-zero): This command allows you to use the first and last subnet in your network design. For example, Class C typically only mask 192 may be provided subnets 64 and 128, but after using ip subnet-zero order, can now be put into subnets 0,64,128 and 192 were used.
In this way, the subnet mask used by each provide more than two subnets.
2. Problems: receiving a router on the interface to which a destination address of the packet 172.16.46.191/26. What the packet router will do?
Answer: discard it. 172.16.46.191/26 mask is 255.255.255.192, which gives the block size is 64. Thus obtained is 0,64,128,192.191 subnet broadcast address of the subnet 128, and for the router, the default is to discard any broadcast packet.
Note: The router will forward the packet source address is broadcast address, but does not forward the packet destination address is a broadcast address.