H3C Technologies H3C S12500-X Series Switches - Manual (Page 88)

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Figure 29 shows the relationship between the user program, DNS client, and DNS server.
The DNS client is made up of the resolver and cache. The user program and DNS client can run on the
same device or different devices, but the DNS server and the DNS client usually run on different devices.
Dynamic domain name resolution allows the DNS client to store latest DNS entries in the dynamic
domain name cache. The DNS client does not need to send a request to the DNS server for a repeated
query within the aging time. To make sure the entries from the DNS server are up to date, a DNS entry
is removed when its aging timer expires. The DNS server determines how long a mapping is valid, and
the DNS client obtains the aging information from DNS responses.
DNS suffixes
You can configure a domain name suffix list so that the resolver can use the list to supply the missing part
of an incomplete name.
For example, you can configure com as the suffix for aabbcc.com. The user only needs to enter aabbcc
to obtain the IP address of aabbcc.com because the resolver adds the suffix and delimiter before passing
the name to the DNS server.
The name resolver handles the queries based on the domain names that the user enters:
• If the user enters a domain name without a dot (.) (for example, aabbcc), the resolver considers the
domain name a host name and adds a DNS suffix before performing the query operation. If no
match is found for the domain names with any configured suffix, the resolver uses the user entered
domain name (for example, aabbcc) to query the IP address.
• If the user enters a domain name with a dot (.) among the letters (for example, www.aabbcc), the
resolver directly uses this domain name for the query operation. If the query fails, the resolver adds
a DNS suffix for another query operation.
• If the user enters a domain name with a dot (.) at the end (for example, aabbcc.com.), the resolver
considers the domain name an FQDN and returns the successful or failed query result. The dot at
the end of the domain name is considered a terminating symbol.
The device supports static and dynamic DNS client services.
If an alias is configured for a domain name on the DNS server, the device can resolve the alias into the
IP address of the host.
DNS configuration task list
Tasks at a glance
Perform one of the following tasks:
• Configuring the IPv4 DNS client
• Configuring the IPv6 DNS client
(Optional.) Specifying the source interface for DNS packets
(Optional.) Configuring the DNS trusted interface
(Optional.) Setting the DSCP value for outgoing DNS packets