H3C S7500 Series Operation Manual page 885

Operation Manual – DNS
H3C S7500 Series Ethernet Switches
result (either successful or failed) is found. Finally, the resolution result is returned
to the DNS client.
4) The DNS client performs the next operation according to the result.
User
program
Figure 1-1 Dynamic DNS resolution
Figure 1-1
server.
The resolver and cache compose the DNS client. The user program can run on the
same device as the DNS client or a different device, while the DNS server and the DNS
client must run on different devices.
Dynamic DNS resolution allows the DNS client to store the latest successful
name-to-address mappings into the dynamic domain name cache. So there is no need
to send a request to the DNS server for query of 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 interval, and the
DNS client obtains the information from DNS messages.
II. 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 enter "aabbcc" to obtain the IP address of
aabbcc.com, because the resolver will automatically add the suffix and delimiter before
passing the name to the DNS server.
When a user enters a domain name:
If there is no dot in the domain name, such as aabbcc, the resolver will 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., it indicates
that no DNS suffix needs to be added and the resolver will use this domain name
Request
Resolver
Response
Read Save
Cache
DNS client
shows the relationship between the user program, DNS client and DNS
R equest
R esponse
DNS server
1-2
Chapter 1 DNS Configuration