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CITA 310 Section 1

Learn how DNS works to map host addresses to IP addresses on the Internet, and troubleshoot DNS configurations. (500 characters)

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CITA 310 Section 1

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  1. CITA 310 Section 1 Name Resolution

  2. Understanding the DNS • DNS is used to map host addresses to IP addresses on the Internet • Also called name resolution or address resolution • Whenever a host is added, a configuration file has to be changed • A host represents a service on a server such as a Web server • There can be many hosts on a single computer

  3. Clients • On your PC, the TCP/IP configuration contains the address(es) of your DNS server(s) • Whenever you use a URL, whether in a browser, or a utility such as ping, DNS is used

  4. Domain Namespaces • The root level domain is "." • Significant in creating DNS files • Top-level domains include com, org, fr • Second-level domains are often owned by companies and individuals • google.com, canton.edu

  5. Domain Namespaces • Second-level domains, such as canton.edu have control over naming within their domain • Create hosts such as www, mail • A name such as www.canton.edu is a fully qualified domain name (FQDN)

  6. Top-Level Domains • .biz - businesses • .info - anyone can register • .name - must register first and last name • .pro - for professionals • .aero, .museum, .coop are controlled by organizations

  7. Host Names • Can be different from the name of the computer • Many hosts can be associated with the same Web server

  8. How DNS Works

  9. DNS Components • Name server – also known as DNS server • supports name-to-address and address-to-name resolution • Name resolver – also called DNS client • Can contact DNS server to lookup name • Used by browsers, e-mail clients, and client utilities such as ping and tracert

  10. DNS Servers that Define the Internet • Primary and secondary servers store the host names used on the Internet • Caching and forwarding servers search the Internet for host names

  11. Primary and Secondary Servers • Primary Server • Defines the hosts for the domain • Maintains the database for the domain • It has authority for the domain • Secondary Server • Gets data from primary server • Provides fault tolerance and load distribution • Required for Internet domains

  12. Primary and Secondary Servers • If you use DNS, you will often work with your ISP • In a simple environment, the ISP will have the primary and secondary DNS servers • You contact them for changes • You can also split the servers • ISP has primary, you have secondary • You have primary, ISP has secondary

  13. Resolve Host Names • Caching Server • Resolves host names • Caches (saves) the results • Automatically installed when DNS is installed • No configuration necessary • Forwarding Server • Caching server that has access to the Internet and forwards traffic from other caching servers

  14. Caching and Forwarding Servers

  15. Zones • A zone is a part of the domain namespace • For a domain as small as technowidgets.com, the domain name represents a single zone • For large organizations (such as IBM), subdomains can be divided into separately maintained zones • Each zone typically has a separate DNS

  16. Zones • Zones must be contiguous • There must be one primary DNS server in each zone (plus a secondary server) • Each zone can have multiple secondary DNS servers

  17. Zone File Configuration • Forward Lookup • These zones contain entries that map names to IP addresses • Reverse Lookup • These zones contain entries that map IP addresses to names

  18. Common DNS Records

  19. Forward Lookup Zone Example $TTL 86400 @ IN SOA web1.technowidgets.com. admn.technowidgets.com. ( 2002072100 ; Serial 28800 ; Refresh 14400 ; Retry 3600000 ; Expire 86400 ) ; Minimum IN NS web1 IN A 192.168.0.100 IN MX 10 mail.technowidgets.com. web1 IN A 192.168.0.100 www IN CNAME web1 research IN A 192.168.0.150 IN MX 10 mail mail IN A 192.168.0.200

  20. Reverse Lookup Zone Example $TTL 86400 @ IN SOA web1.technowidgets.com. admn.technowidgets.com. ( 2002072100 ; Serial 28800 ; Refresh 14400 ; Retry 3600000 ; Expire 86400 ) ; Minimum IN NS web1 100 IN PTR web1.technowidgets.com. 150 IN PTR research.technowidgets.com. 200 IN PTR mail.technowidgets.com.

  21. Finished DNS Configuration in Windows

  22. Troubleshooting DNSping • ping displays name resolution even if the computer cannot be contacted

  23. Troubleshooting DNSnslookup • nslookup can display information from the DNS server

  24. Troubleshooting DNSdig – available on Linux

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