3Com Switch 8800 Configuration Guide Chapter 14 DNS Configuration
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Chapter 14 DNS Configuration 14.1 Introduction to DNS
Used in the TCP/IP application, Domain Name System (DNS) is a distributed database
which provides the translation between domain name and the IP address. In this way,
the user can use domain names that are easy to memorize and meaningful, and never
needs to keep obscure IP addresses in mind.
There are two kinds of domain name resolutions: static domain name resolution and
dynamic domain name resolution, which supplement each other in real application. On
resolving a domain name, use the static resolution first. If it fails, use the dynamic
resolution method. You can put some common domain names into the static domain
name resolution table to raise the domain name resolution efficiency greatly.
14.1.1 Static Domain Name Resolution
Static domain resolution is to establish maps between domain name and the IP address
manually. When you perform some applications using domain names, the system can
obtain the IP address of the specified domain name by searching the static domain
name resolution table.
14.1.2 Dynamic Domain Name Resolution
Dynamic domain name resolution is implemented by inquiring the domain name server.
As a DNS client, the switch sends an inquiry request to the domain name server, and
the domain name server searches the related IP address of the domain name in its own
database and sends it back to the switch. If the domain name server judges that the
domain name does not belong to the local domain, it forwards the request to the upper
level domain name resolution server till the resolution is finished.
Dynamic domain name resolution supports the buffer function. It stores each
successful domain name/IP address mapping that is resolved dynamically in the
dynamic domain name buffer. When the same domain name is searched next time, it
can be read directly from the buffer, without requesting the domain name server. The
aged mapping in the buffer is deleted after a certain period of time to ensure the
updated contents can be got from the domain name server timely. The aging time is set
by the domain name server and obtained by the switch from the protocol packet.
Dynamic domain name resolution supports the domain name suffix list function. You
can set some domain name suffixes beforehand and input part of the domain name
field during the domain name resolution, then the system adds different suffixes to the
input domain name automatically for resolution. For example, if a user wants to search
the domain name “3Com.com”, he can configure the “com” in the suffix list and input