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3com WX3000 User Manual

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Figure 1-1 Dynamic domain name resolution 
Request
Response
Response
Request
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DNS client
DNS server
Resolver
Cache
User 
program
 
 
 shows the relationship between user program, DNS client, and DNS server. 
The resolver and cache comprise the DNS client. The user program and DNS client run on the same 
device, 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 name and IP 
address in the dynamic domain name cache of the DNS client. There is no need to send a request to the 
DNS server for a repeated query request 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 information from DNS messages. 
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 not complete. The resolver can supply the missing part (automatic domain name 
addition). 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. 
z 
If there is no dot in the domain name, such as aabbcc, the resolver will consider this as a host name 
and add a DNS suffix before processing. The original name such as aabbcc is used if all DNS 
lookups fail. 
z 
If there is a dot in the domain name, such as www.aabbcc, the resolver will use this domain name 
to do DNS lookup first. If the lookup fails, the resolver adds a DNS suffix for another lookup. 
z 
If a dot is at the end of the domain name, such as “aabbcc.com.”, the resolver will consider this as 
a fully qualified domain name and return the result, success or failure. Hence, the dot (.) is called 
the terminating symbol. 
Currently, the device supports both static and dynamic DNS clients. 
Configuring Domain Name Resolution 
Configuring Static Domain Name Resolution 
Follow these steps to configure static domain name resolution: