uni
Problem: internet hosts and routers have both
- a IP address (IPv4), used for addressing datagrams
- a “name”, used by humans (like www.google.com)
How do we map between IP address and name, and vice versa?
solution: the DNS
The Domain Name System (DNS) is a distributed database implemented in hierarchy of many name servers.
Application-layer protocol: hosts and name servers communicate to resolve names (addres-name translation).
Registering a subdomain means linking it univocally to a IP address, registering it in the DNS database.
DNS services
- hostname to IP address translation
- host aliasing
- mail server aliasing
- load distribution
- replicated web servers: many IP addresses correspond to one name
DNS structure
The DNS is a distributed, hierarchical database:
- ROOT: root DNS servers
- TOP LEVEL DOMAIN: .com DNS servers, .org DNS servers ecc
- AUTHORITATIVE: yahoo.com DNS servers, google.com DNS servers, pbs.org DNS servers ecc
ICANN
The distributed DNS server is managed by Internet Corporation for Assigned Names and Numbers (ICANN), which also defines what the top layer domains* are.
Local DNS name servers
Also called default name server, these are installed into each ISP and they act as a sort of proxy DNS server, they have a local cache of recent name-to-address translations pairs, BUT it may be out of date!