Domain Name Services Oakton Community College CIS 238

DNS – Hierarchical naming system used to resolve host name to IP address mapping – Contains resource records – Primary name resolution method in Windows 2000 Host files and DNS perform the task of translating from names (host names) to IP addresses Host names – Simple names used as aliases for IP addresses

Host Files Text files that contain host name to IP address mapping Used to perform host name to IP address resolution Precursor to the DNS system Without host name resolution, users cannot access Internet or intranet resources via Fully Qualified Domain Names (FQDN)

DNS Structure Root-level domain – Represented by a period – Usually not shown on FQDN Top-level domains Second-level domains Subdomains Individual hosts

DNS Hierarchical Structure

Top-level Domains Organizational domains created by designers of the Internet to simplify the naming and logical structure of the DNS namespace

Second-level Domains and Subdomains Second-level domains – Where companies register their names with a name registration company – Gives the company authority to create subdomains to further divide the domain namespace

DNS Zones Zone of authority – Portion of the DNS namespace that an organization controls DNS zone – Portion of the DNS namespace that can be administered as a single unit – Each zone has a primary name server that holds the DNS zone file

DNS Zones Primary name servers – Hold a read/write copy of the zone file Secondary name servers – DNS servers configured to hold a read-only copy of the primary name server’s DNS zone file All networks should minimally have a primary and a secondary DNS name server, or two DNS servers configured to use Active Directory integrated zones

DNS Servers Can be configured as caching-only servers Hold two types of DNS zones: – Forward lookup zones (host name to IP address mapping) – Reverse lookup zones (IP address to host name mappings) Roles available to computers in DNS system – DNS servers that answer client requests – DNS resolvers; clients that initiate requests Types of requests or queries – Recursive – Iterative – Inverse

Resource Records Used within the actual zone files to point to particular hosts

Configuring the DNS Server Configuring a root name server Configuring primary and secondary zones Configuring caching-only servers Configuring delegation for use with a subdomain Configuring the DNS service to allow dynamic updates

Configuring a Root Name Server Root name server – Server that holds information about the overall Internet domain name servers Choose a primary zone to configure a root zone server Choose a zone type – Active Directory integrated – Standard primary – Standard secondary Name the zone

Configuring Primary and Secondary Zones DNS server – Is configured as a primary name server for a particular zone or as a secondary or back-up, name server for a zone – Can also be the primary server for one zone and the secondary server for another After creating subdomains, delegate authority for a zone via the New Delegation Wizard Active Directory integrated zones – Allow storage and replication of the DNS database within the AD database – Ease the administrative tasks associated with manually setting up replication between primary and secondary name servers

Configuring Caching-only Servers Caching-only server – Is not authoritative for any particular DNS zone; is not configured to hold a primary or secondary zone – Forwards DNS requests and then caches the DNS resolutions Load the DNS server service Configure forwarder addresses

DNS Client Configuration nsswitch.conf – DNS resoluton sequence resolv.conf – domain name, nameserver sequence (timeout only) For clients with static IP addresses – Manually configure a Preferred DNS server and an Alternate DNS server in TCP/IP properties DNS configuration tab for Windows 95/98 clients For DHCP clients – Configure DNS options for the scope that the client will obtain an IP address from

Zone settings SOA TTL Settings - Cache entries are maintained for a length of time determined by the time-to-live setting of the zones on a server - By default, TTL is one day - Refresh interval - Retry interval Serial # Zone Transfer setting Secure DNS

Debugging DNS nslookup dig