Many thanks for all the quick and helpful answers! Indeed it seems to be related to the DNS. On CentOS, after connecting to the wireless network, I hacked the /etc/resolv.conf generated by the NetworkManager and added Google Public DNS to it. I could then access all websites via their domain names. Unfortunately, there are plenty of other issues with this particular network (disconnecting all the time, also on windows), so I was not in a position to test a more stable configuration.