The other network (network B) most probably has a firewall implemented, which is configured to block ICMP packets (pings). This is most likely the case if the network is in a university, at work, or maybe even a (smart) coffee shop.
ping 188.8.131.52, an IP should be mentioned in that message you got. I'm betting that that IP is 192.168.1.1, so the error would be something like
reply: 192.168.1.1 destination host unreachable. Also, to be more certain, you can do a traceroute. This shows you the path that your ping travels, so we can find exactly where it stops. So, if you run the command
traceroute -n 184.108.40.206, you'll probably get something like this:
I think you might need to install traceroute using
sudo apt-get install traceroute.
alaa@aa-UBUNTU:~$ traceroute -n 220.127.116.11
traceroute to 18.104.22.168 (22.214.171.124), 30 hops max, 60 byte packets
1 192.168.1.1 1.204 ms 1.953 ms 2.101 ms
2 * * *
3 * * *
...and those stars will just keep on coming. This means that your ping went to 192.168.1.1, but then it stopped, it hit a wall, so you'll never be able to ping 126.96.36.199.
Also, this has nothing to do with DNS, because you're pinging an IP, not a hostname like google.com. DNS is a system that merely translates the words
google.com to something like
188.8.131.52. If there was something wrong with your DNS settings,
ping google.com would return something like this:
ping: unknown host google.com, but
ping 184.108.40.206 would not, because you're already pinging a direct IP.
I suggest you revert the changes you made to NetworkManager.conf.