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  1. 1. Networking Basics: DNS • IP addresses are usually paired with more human-friendly names: Domain Name System (DNS). 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. 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. 3. Networking Basics: DNS, con’t. • Network Solutions (previously the InterNic) registers domain names – See Other registrars include • 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. 4. DNS Overview: If DNS Servers Could Talk…
  5. 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 Also available via web browser at – nslookup and host (on UNIX machines) – tell you IP address information for a particular hostname on the internet (e.g. nslookup or host
  6. 6. DNS Exercise • What are IP addresses of the DNS servers that contain information about • What are the IP address of: – – –
  7. 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. 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. = – MX Records: give the IP address of the mail host for a hostname or domain (I.e. “Mail addressed to anyone gets handled by the mail server
  9. 9. Review: Network Tools • Ping (Windows and UNIX) • Traceroute (tracert on Windows, traceroute on UNIX) • Nslookup (UNIX only) • Host (UNIX only)