Networking Basics: DNS

1
Networking Basics DNS

• IP addresses are usually paired with more
  human-friendly names Domain Name System (DNS).

internet.rutgers.edu
Hostname Organization Top-level domain

• Other top-level domains include .com, .gov, .org,
  etc. There are also country-specific domains
  like .uk, .ca, .jp, etc.

2
Networking Basics DNS, cont.

• Domain name information is maintained through a
  distributed database of host name/ IP address
  pairing.
• The Network Information Center (NIC) manages the
  top-level domains, delegates authority for
  second-level domains, and maintains a database of
  registered name servers for all second-level
  domains.
• Host name assignments maintained through zone
  files on primary DNS server. Secondary DNS server
  gets zone file from primary server.

3
Networking Basics DNS, cont.

• Network Solutions (previously the InterNic)
  registers domain names See http//www.networksol
  utions.com. Other registrars include
  Register.com
• Costs range from 20 to 50 per year.
• ISPs beginning to offer domain name registration
  as part of other packages.
• Need to register a primary and secondary domain
  name servers for your domain and arrange to have
  zone files created on DNS servers.

4
DNS Overview If DNS Servers Could Talk
5
Networking Basics DNS Tools

• There are several tools for for monitoring DNS
  information
• whois tells you the owner and primary DNS
  servers associated with a domain (e.g. whois
  yahoo.com). Also available via web browser at
  www.networksolutions.com.
• nslookup and host (on UNIX machines) tell you
  IP address information for a particular hostname
  on the internet (e.g. nslookup www.yahoo.com or
  host www.rutgers.edu)

6
DNS Exercise

• What are IP addresses of the DNS servers that
  contain information about rutgers.edu?
• What are the IP address of
• www.retaildecisions.com
• abusaday.admin.cju.com
• www.linux.org

7
Sending DNS Queries Messages

• A DNS query packet is formed at the application
  layer.
• DNS is unique, as it can utilize either UDP/IP or
  TCP/IP to send a message.
• Uses UDP by defult if message is too bit (512
  bytes), it will use TCP

8
Types of DNS Records

• There are several types of DNS records that are
  kept by DNS servers
• A Records give the IP address for a hostname.
• CNAME Records give aliases for hostanmes (i.e.
  web.domain.com www.domain.com)
• MX Records give the IP address of the mail host
  for a hostname or domain (I.e. Mail addressed to
  anyone _at_yahoo.com gets handled by the mail server
  mail.yahoo.com)

9
Review Network Tools

• Ping (Windows and UNIX)
• Traceroute (tracert on Windows, traceroute on
  UNIX)
• Nslookup (UNIX only)
• Host (UNIX only)