H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 82)

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3. The DNS server looks up the corresponding IP address of the domain name in its DNS database.
If no match is found, the server sends a query to a higher level DNS server. This process continues
until a result, whether successful or not, is returned.
4. After receiving a response from the DNS server, the DNS client returns the resolution result to the
application.
Figure 27 Dynamic domain name resolution
Figure 27 shows the relationship between the user program, DNS client, and DNS server.
The DNS client is made up of the resolver and cache. The user program and DNS client can run on the
same device or different devices, but the DNS server and the DNS client usually run on different devices.
Dynamic domain name resolution allows the DNS client to store latest mappings between domain names
and IP addresses in the dynamic domain name cache. The DNS client does not need to send a request
to the DNS server for a repeated query next time. The aged mappings are removed from the cache after
some time, and latest entries are required 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.
DNS suffixes
The DNS client holds a list of suffixes which the user sets. It is used when the name to be resolved is
incomplete. The resolver can supply the missing part.
For example, a user can configure com as the suffix for aabbcc.com. The user only needs to type aabbcc
to obtain the IP address of aabbcc.com because the resolver adds the suffix and delimiter before passing
the name to the DNS server.
• If there is no dot in the domain name (for example, aabbcc), the resolver considers this a host name
and adds a DNS suffix before query. If no match is found after all the configured suffixes are used
respectively, the original domain name (for example, aabbcc) is used for query.
• If there is a dot in the domain name (for example, www.aabbcc), the resolver directly uses this
domain name for query. If the query fails, the resolver adds a DNS suffix for another query.
• If the dot is at the end of the domain name (for example, aabbcc.com.), the resolver considers it a
fully qualified domain name (FQDN) and returns the query result, successful or failed. The dot (.) at
the end of the domain name is considered a terminating symbol.
The device supports static and dynamic DNS client services.
NOTE:
If an alias is configured for a domain name on the DNS server, the device can resolve the alias into the IP
address of the host.
Request
Response Response
Request
Save Read
DNS client
DNS server
Resolver
Cache
User
program