Exercise 3: DNS

Domain Name System or DNS is a hierarchical, distributed database that contains mappings of domain names to various types of data. DNS allows us to use friendly names to easily locate computers and other resources on a TCP/IP-based network.  (http://technet.microsoft.com/en-us/network/bb629410.aspx)

When we access a website, the web server checks it with the DNS Resolver, a built-in component in operating systems. It translates the domain name to its IP address and do the domain name-IP mapping on different databases until it is found.

Functions of DNS include caching and redundancy. DNS resolvers store the answers they get from other DNS servers. Those are added in a cache, an internal database. When you access a same website again, it does not need to look up the host again. Caching and redundancy help DNS to respond faster to queries.

Zone File
Zone file is a part of configuring a DNS server. It describes a DNS zone and contains list of all the hosts in the domain and their corresponding IP address. Here are its parts:

• SOA (Start of Authority) - states that this server is authoritative for the specific domain.
• NS (Name Server) - specifies the name server to use to look up a domain
• MX (Mail Exchange) - specifies mail server/s for the domain
• A (A record) - used for linking FQDN to an IP address
• CNAME (Canonical Name) - assigns aliases to existing A records
• PTR - reveres map IP addresses to an FQDN

For our exercise, we just used SOA, NS, A for forward zone file, and SOA, NS, PTR for reverse.

forward zone file

reverse zone file

named.conf.local 

We learned how to make a domain name for an IP address and connect to other computers using their domain names. We used BIND, a DNS software use to configure a DNS server.

I needed some patience to make this work.

pinging

References:

• http://technet.microsoft.com/en-us/network/bb629410.aspx
• http://www.inetdaemon.com/tutorials/internet/dns/servers/caching.shtml
• http://www.hansenonline.net/networking/zonefile.html