MacBook Pro: DNS works but not ping, http, or https

Approximately twenty hours ago, I shut down my MacBook Pro and got on a plane. At home, everything was working. Now, at my sister’s house, I cannot get anything in Safari nor by ping.

Ping gets “no route to host” for any name or IP address, even when I ping the IP address of the DNS server that successfully resolved the other host names.

To make sure the DNS wasn’t cached, I rebooted, and tried a hostname I knew hadn’t been used in months. The name was resolved, but still, “no route to host.”

It’s not my sister’s router, because I get the same thing when I switch to my iPhone’s hotspot.

It’s not any of the remote hosts, because they are working for the iPad and for my sister.

When I use Fing (a network scanner) on the iPad to examine the network, I see that everything is on 10.0.0.x including a Cisco router.

My iPad and iPhone and her Android and Windows are working fine on the same SSID.

???

Could it be that TCP on the laptop somehow broke in transit while UDP still works?

UPDATE: Totally weird. ifconfig get packet en1 had absolutely no output. tcpdump -s 500 -v -I en1 also did nothing for about a minute, even though I tried a ping in another window (which also did nothing). But then tcpdump started rolling, and it was fairly plain that both sides were trying to do lots of IPv6. Going back to the settings, it had changed itself back to manual. I kept changing it to DHCP, but every time I did anything, it changed back to manual. Eventually, without knowing what I had done differently, it stayed on manual and then everything worked. And the router is definitely 10.0.0.1. SMH.