IP classless & no IP classless

IP classless:
1. The IP classless command acts on the route forwarding process and tells the router to work in a classless environment.
2. It allows the router to forward data packets beyond the boundaries of a class network based on the longest matching entry;
3. When the destination network does not appear in the route table, data packets are forwarded by default instead of simply discarded.
4. If the vro works in a class environment, the firewall discards the data packet when the target network appears in the routing table but no specific network match exists.

When there is no IP classless, assume that there are route records for 10.0.0.0/8, 10.1.0.0/16, and 10.2.0.0/16 in the vro, then the vro receives
An IP packet destined for 10.4.0.0/16 is discarded by the router. The router finds that 10.4.0.0/16 is not in the routing table. It is useless even if there is a default route.
Now, if the IP classless command is started, how will the 10.4.0.0/16 packet be forwarded? It will forward the packet according to the route record of 10.0.0.0/8. Because it is 10.4.0.0/16. Of course, if the route record for 10.0.0.0/8 does not exist in the vro, the package for 10.4.0.0/16 will follow the default route

Add an IP classless command, then the vro becomes a classless routing environment. When the destination data packet arrives, no class matching is performed.No class match, That isLongest Matching PrincipleWhen the longest match is used, the router will give it to the default route and send the data packets through the default route.
When a router receives a data packet whose destination address does not exist in the routing table, it discards the data packet.If you use the default route, you must use the IP classless command, because the remote subnet does not exist in your route table.