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Configuring DDNS
Overview
Although DNS allows you to access nodes in networks using their domain names, it provides only
the static mappings between domain names and IP addresses. When you use the domain name to
access a node whose IP address has changed, your access fails because DNS leads you to the IP
address that is no longer where the node resides.
Dynamic Domain Name System (DDNS) can dynamically update the mappings between domain
names and IP addresses for DNS servers to direct you to the latest IP address corresponding to a
domain name.
DDNS can only dynamically update the mappings between domain names and IPv4 addresses but
not IPv6 addresses.
Figure 206 DDNS networking application
As shown in Figure 206, DDNS works on the client-server model comprising the DDNS client and the
DDNS server.
• DDNS client—A device that needs to update the mapping between the domain name and the
IP address dynamically on a DNS server. An Internet user usually uses the domain name to
access an application layer server such as an HTTP and FTP server. When its IP address
changes, the application layer server runs as a DDNS client that sends a request to the DDNS
server for updating the mapping between the domain name and the IP address.
• DDNS server—Informs the DNS server of latest mappings. When receiving the mapping
update request from a DDNS client, the DDNS server tells the DNS server to re-map between
the domain name and IP address of the DDNS client. Therefore, the Internet users can use the
same domain name to access the DDNS client even if the IP address of the DDNS client has
changed.
The DDNS update process does not have a unified standard and depends on the DDNS server that
the DDNS client contacts. The well-known DDNS service providers include www.3322.org,
www.oray.cn (also known as the PeanutHull server), and www.dyndns.com.
The device can act as a DDNS client to dynamically update the latest mapping between its domain
name and IP address on the DNS server through a DDNS server at www.3322.org or www.oray.cn
for example.
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