HP VPN Firewall Appliances Network Management Configuration Guide

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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.
Because DDNS is supported by IPv4 DNS but not supported by IPv6 DNS, it can be used to update the
mappings between domain names and IPv4 addresses only.
DDNS networking application
As shown in Figure 149, DDNS works on the client-server model.
• DDNS client—A device that needs to dynamically update the mapping between the domain name
and the IP address on the DNS server when the client's IP address changes. An Internet user
typically uses the domain name to access an application layer server such as an HTTP server or an
FTP server. When its IP address changes, the application layer server runs as a DDNS client that
sends a request to the DDNS server to update 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 the 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.
Figure 149 DDNS networking application
HTTP server
DDNS client
DDNS server
DNS server
IP network
HTTP client