Yesterday, I briefly learned about the DHCP.
I am at the starbucks cafe right now. I am using 172.30.0.189 255.240.0.0 which was received by DHCP server. I changed my IP to 172.30.0.190 255.240.0.0. The result was "NO Internet Connection" haha. If DHCP server's pool includes 172.30.0.190 255.240.0.0 and has not given that IP address, why cannot I use that IP to be connected to the Internet? Can anyone kindly explain to me what is actually going on if I change my IP to 172.30.0.190 255.240.0.0 from the IP I received from the DHCP server?
For security reasons, starbucks have probably configured their wireless to only allow client that obtain ip address via DHCP to connect. If the wireless network does not see DHCP negotiations from the client, it does not allow the client to join the network.
Although you set a valid ip address, the wireless network did not accept traffic from that ip because it was not obtained via DHCP.
A subnet with subnet mask 255.240.0.0 is big, we should not use a subnet with that mask because the broadcast domain is huge and many IP addresses are wasted. I think they use 1 subnet for all the areas inside that branch. They could have reasons for that implementation, my personal opinion they should use subnetting or VLSM.
Now probably they are just allowing the subnet 172.30.0.0/24 into the NAT statement to reach Internet access, so that could be reason due to you did not get Internet access from the other subnet into the supernet.