Dynamic Domain Name Resolution - H3C S5500-EI series Operation Manual

Operation Manual – DNS
H3C S5500-EI Series Ethernet Switches

1.1.2 Dynamic Domain Name Resolution

I. Resolving procedure
Dynamic domain name resolution is implemented by querying the DNS server. The
resolution 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 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, 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 a
response from the DNS server.
Figure 1-1 Dynamic domain name resolution
Figure 1-1
server.
The resolver and cache comprise the DNS client. The user program and DNS client
can run on the same device or different devices, while 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.
II. DNS suffixes
The DNS client normally 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.
shows the relationship between the user program, DNS client, and DNS
1-2
Chapter 1 DNS Configuration