Ping of Death - when so many pings for the purpose of disruption that no legitimate internet traffic can get through, this was an issue about 15 years ago, and to this day ICMP is still blocked on many university networks
Applications like Firefox and the email client do not make dns requests, dns requests happen on the operating system level. It has a DNS resolver and a cache. Sometimes you need to hard refresh to clear the cache.
/etc/resolve.conflists the current dns server for resolving dns requests
/etc/hostsis a local list of dns entries
/etc/nsswitch.confis the config of the GNU Name Service Switch