3Com 7757 Configuration Manual page 832

832 C 76: DNS C
HAPTER ONFIGURATION
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Figure 213 Dynamic DNS resolution
Request
User
program
Response
Figure 213 shows the relationship between the user program, DNS Client and DNS
Server.
The resolver and cache compose the DNS Client. The user program runs on the
same machine as the DNS client, while the DNS Server and the DNS Client must
run on different machines.
Dynamic DNS resolution allows the DNS Client to store the latest name-to-address
mappings in the dynamic domain name cache. So there is no need to send a
request to the DNS Server for the same domain next time. The DNS Client removes
aged mappings from the cache, so as to obtain updated mappings from the DNS
Server. The setting on the DNS Server determines the aging time, and the DNS
Client gets the information from DNS messages.
DNS suffix list
The DNS Client normally holds a DNS suffix list where you can define some
domain name suffixes. It is used when the name to be resolved is not complete.
The resolver can use the list to supply the missing part. For example, you can
configure a suffix "com" in the list, and users only need to input "aabbcc" to get
the IP address of aabbcc.com, for the resolver will automatically add the suffix and
delimiter before passing the name to the DNS Server.
When a user input a domain name:
If there is no dot in the domain name, such as "aabbcc", the resolver will
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consider this as a host name and add a suffix to the name before performing
DNS lookup. If all the suffixes in the DNS suffix list have been tried but no DNS
lookup succeeds, the resolver will use the original name (such as aabbcc) for a
DNS lookup.
If there is a dot in the domain name, such as "www.aabbcc" or "aabbcc.", the
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resolver will first use this domain name to perform DNS lookup before trying
any other suffix.
Currently, the Switch 7750 Ethernet switches support both static and dynamic
domain name resolution on the DNS Client.
If you have configured aliases for domain names on the DNS server, the Ethernet
switch can resolve a host IP address according to its alias.
Request
Resolver
Response
DNS server
Read Save
Cache
DNS client