H3C S3610 Series Operation Manual page 3

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Operation Manual – DNS

H3C S3610&S5510 Series Ethernet Switches

A user program sends a name query to the resolver of the DNS client.

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.

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 success or failure, is returned.

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 machine or different devices, while the DNS server and the DNS

client usually must 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.

For example, a user can configure com as the suffix for aabbcc.com. The user only

needs to type aabbcc to get the IP address of aabbcc.com. The resolver can add 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 will

consider this a host name and add a DNS suffix before query. If no match is found

shows the relationship between the user program, DNS client, and DNS

1-2

Chapter 1 DNS Configuration

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S5510 series