The Domain Name System (DNS) is a hierarchical system that provides the IP addresses that correspond to a given Fully Qualified Domain Name (FQDN, often called a hostname or domain name). At the top of the tree structure are thirteen “root” Domain Name Servers that have the primary and secondary IP addresses of the DNS Authorities for all domains on the Internet.
Authoritative DNS Establishing Redundancy with the PowerLink Pro Series
IntroductionThe intent of this paper is to give the reader a brief introduction to how the Domain Name System works and how redundancy is accomplished when utilizing the PowerLink as the DNS authoritative server at the client's site. It is not the intent of this paper to be a complete technical description of the Domain Name System.
DNS OverviewThe Domain Name System is a hierarchical system that provides the IP address that corresponds to a given Fully Qualified Domain Name (abbreviated FQDN, often called a hostname or domain name). For example, www.astrocorp.com is at IP address 64.122.215.18. At the top of the tree structure there are thirteen "root" Domain Name Servers that have the primary and secondary IP addresses of the DNS Authorities for all domains on the Internet. The DNS Authority is the server that contains the specific IP address or addresses for a given domain name. At the bottom of the tree structure there are caching name servers that lookup and store records for local queries. When a domain name is registered on the Internet, the primary and secondary addresses of its DNS Authority are placed in all 13 "root" Domain Name Servers on the Internet. The address of the host that corresponds to the FQDN is kept updated in the DNS Authoritative server designated for that site. A typical sequence for a DNS lookup would involve a user's machine sending a hostname to the caching server that was designated in the configuration of that machine. If the caching server does not have the IP address for that hostname, or if the time-to-live (TTL) has expired for the cached record, it will query a root Domain Name Server to obtain the addresses of the DNS Authority for that domain. The caching server will then query the DNS Authority and be given the requested record, including the associated IP address and TTL. This address is passed on to the requesting host and cached for future reference. If the caching server receives more than one IP address for a given hostname, it should rotate through these addresses in response to client queries. Changes of address for the DNS Authority at the "root" Domain Name Servers typically take from 1 to 2 days to take effect and propagate through the Internet. Changes in records provided by DNS Authorities take effect when the TTL expires at a caching name server.
page 1A Typical NetworkThe diagram below depicts the typical process by which a client machine obtains the location of a destination host (www.astrocorp.com) by means of DNS.
1. C lient's browser initiates a query to the caching DNS server, designated in its configuration file, requesting the IP address for "www.astrocorp.com". 2. If the Caching DNS Server has a current address record for www.astrocorp.com, it immediately returns the IP address the client host. If the Caching server does not have information for www.astrocorp.com, it contacts a root DNS server and requests the record containing the addresses of the primary and secondary DNS authorities for "astrocorp.com". 3. A root name server is one of thirteen root name servers that service the Internet. These servers know where the caching server needs to look next to find the information it needs to resolve www.astrocorp.com. Like following links in a chain, the caching name server navigates the DNS hierarchy until it obtains the name server records for astrocorp.com. 4. The caching name server sends its request for www.astrocorp.com to one of the name servers designated as the authority for astrocorp.com. 5. The DNS authority returns its record for www.astrocorp.com that includes the IP address of the host and a TTL value. A sequence number allows the caching DNS server to determine if the record has changed since it was last updated. 6. The Caching DNS server sends the IP address of www.astrocorp.com to the client machine. 7. The client establishes communication directly with www.astrocorp.com.
page 2A Network Using the PowerLinkShown below is a diagram depicting the same situation as above, but with a PowerLink being utilized to aggregate 2 WAN lines and provide inbound failover and load-balancing for www.astrocorp.com. In this example, steps 1-3 are identical to the previous example.
4. T he caching DNS server will then request the www record from the PowerLink, which is functioning as both the primary and secondary authoritie... [download for more]
