1. Networking Basics: DNS IP addresses are usually paired with more human-friendly names: Domain Name System (DNS). internet.rutgers.edu HostnameOrganizationTop-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 http://www.networksolutions.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. 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)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)