Operation Manual – DNSH3C S5500-EI Series Ethernet Switches Chapter 1 DNS Configuration1-21.1.2 Dynamic Domain Name ResolutionI. Resolving procedureDynamic domain name resolution is implemented by querying the DNS server. Theresolution procedure is as follows:1) A user program sends a name query to the resolver of the DNS client.2) The DNS resolver looks up the local domain name cache for a match. If a match isfound, it sends the corresponding IP address back. If not, it sends a query to theDNS server.3) The DNS server looks up the corresponding IP address of the domain name in itsDNS database. If no match is found, it sends a query to a higher level DNS server.This process continues until a result, whether successful or not, is returned.4) The DNS client returns the resolution result to the application after receiving aresponse from the DNS server.Figure 1-1 Dynamic domain name resolutionFigure 1-1 shows the relationship between the user program, DNS client, and DNSserver.The resolver and cache comprise the DNS client. The user program and DNS clientcan run on the same device or different devices, while the DNS server and the DNSclient usually run on different devices.Dynamic domain name resolution allows the DNS client to store latest mappingsbetween domain names and IP addresses in the dynamic domain name cache. Thereis no need to send a request to the DNS server for a repeated query next time. Theaged mappings are removed from the cache after some time, and latest entries arerequired from the DNS server. The DNS server decides how long a mapping is valid,and the DNS client gets the aging information from DNS messages.II. DNS suffixesThe DNS client normally holds a list of suffixes which can be defined by users. It is usedwhen the name to be resolved is incomplete. The resolver can supply the missing part.
