3Com 4210 PWR Configuration Manual page 552

550 C 48: DNS C
HAPTER ONFIGURATION
Figure 197 Dynamic domain name resolution
Request
User
program
Response
Figure 197 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.
If there is no dot in the domain name, such as aabbcc or aabbcc., it indicates
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that no DNS suffix needs to be added and 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.
If there is a dot in the domain name, such as www.aabbcc, the resolver will use
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this domain name to do DNS lookup first. If the lookup fails, the resolver adds a
DNS suffix for another lookup.
Request
Resolver
Response
DNS server
Read Save
Cache
DNS client