Dynamic domain name resolution

Resolution process

  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 is found, it sends the corresponding IP address back. If not, it sends a query to the DNS server.

  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 26: Dynamic domain name resolution

Figure 26 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. There is no 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 can be defined by users. 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.

The switch supports static and dynamic DNS client services.

[NOTE: ]


If an alias is configured for a domain name on the DNS server, the switch can resolve the alias into the IP address of the host.