First, a sample from a Shehiren teacher's book is referenced:
Host H1 the process of sending packets to H2:
First, with the subnet mask in the subnet:255.255.255.128 and target host H2 IP address:128.30.33.128 and get network number
: 128.30.33.128. Obviously this does not match the network number of Subnet 1:128.30.33.0.
The datagram is then forwarded by the default route R1 Subnet 1. At this point, R1 will look for its own routing table. Think of the host address and subnet mask of the H2, and when you want to match the result with a destination network address, send the datagram to the subnet (that is, Subnet 2).
So the problem is, we know that the same IP address and different subnet masks are likely to get the same network address. What subnet should the datagram be delivered to at this time?
PS: What is the approximate content of a routing table?
"IP layer Packet Forwarding process" in the case of subnetting, packet forwarding algorithm.