Slide 91
Slide 91 text
Recursion Round 1
• DNS query to 198.41.0.4
• com. IN NS a.gtld-servers.net
• com. IN NS b.gtld-servers.net.
• a.gtld-servers.net. IN A 192.5.6.30
• b.gtld-servers.net. IN A 192.33.14.30
Our ISP's DNS server has the hardwired list of the 13 root servers, called the root hint file,
managed by IANA. It picks one of those, let's say a.root-server.net, and sends it a new
request for the A record for www.google.com. Just like our DNS query, this new query gets
encoded in a DNS message, wrapped in UDP, IP, and Ethernet headers, sent on to the local
network, across several more backbone links from our ISP to other ISPs, eventually reaches
the root server which makes a response packet and sends it back across the internet.
Eventually we get a response like this. gtld-servers.net are the TLD-level DNS servers for
the .com domain. Instead of being run by different organizations like the root servers, these
are all run by Verisign as part of their ownership of the .com TLD.