Junos' Approach to Dynamic DNS (DDNS)

Dynamic DNS (DDNS) is a method of automatically updating a name server in the Domain Name System (DNS), often in real time, with the active DDNS configuration of its configured hostnames, addresses or other information. This is particularly useful for systems with dynamic IP addresses. In this blog post, we will explore how Junos, the operating system used in Juniper Networks devices, approaches DDNS.

Understanding DDNS

Before we delve into Junos' approach, let's first understand what DDNS is. In a typical DNS setup, you have a domain name and it is associated with a static IP address. However, not all devices have a static IP address. Some devices have dynamic IP addresses that change over time. This is where DDNS comes in. DDNS allows the device to automatically update the DNS record when its IP address changes.

Junos and DDNS

Junos OS does not natively support DDNS, but it can be configured to work with DDNS services. This is typically done by using scripts that run on the Junos device. These scripts will communicate with the DDNS service to update the DNS record when the IP address changes.

Here is an example of how you might configure a Junos device to work with a DDNS service:

set system scripts op file update-ddns.slax
set system scripts commit file update-ddns.slax

In this example, update-ddns.slax is a script that communicates with the DDNS service. This script would be written in the SLAX scripting language, which is a scripting language specifically designed for automating tasks in Junos.

The script might look something like this:

version 1.0;

ns junos = "http://xml.juniper.net/junos/*/junos";
ns xnm = "http://xml.juniper.net/xnm/1.1/xnm";
ns jcs = "http://xml.juniper.net/junos/commit-scripts/1.0";

import "../import/junos.xsl";

match / {
    <op-script-results> {
        var $hostname = "myhostname";
        var $username = "myusername";
        var $password = "mypassword";
        var $interface = "ge-0/0/0";
        var $ip-address = {
            var $rpc = <get-interface-information> {
                <interface-name> $interface;
            var $result = jcs:invoke($rpc);
        var $url = "https://myddnsservice.com/update?hostname=" _ $hostname _ "&myip=" _ $ip-address;
        var $curl-command = "curl -u " _ $username _ ":" _ $password _ " " _ $url;
        <command> $curl-command;

In this script, we first define some variables for the hostname, username, password, and interface. We then get the current IP address of the interface using the get-interface-information RPC. We construct the URL for the DDNS service, and then we use the curl command to send a request to the DDNS service to update the DNS record.


While Junos does not natively support DDNS, it can be configured to work with DDNS services using scripts. This allows Junos devices with dynamic IP addresses to automatically update their DNS records, ensuring that they can always be reached even if their IP address changes. This is just one example of the flexibility and power of Junos.

© Ben Jacobson.RSS