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, con’t.
• 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, con’t.
• Network Solutions (previously the InterNic)
registers domain names – See
http://www.networksolutions.com. Other
registrars include Register.com
• Costs range from $20 to $50 per year.
• ISP’s 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 @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)