Makers Blog

Access to PlcNext webserver on DHCP

Martin PLCnext Team 24 November 2020 min. read
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 would like to share an application story from Ignacio Aláez, a Solution Engineering Expert from Phoenix Contact Spain, which might be of interest to the PLCnext Community.

As part of a project we have the problem of accessing a Plcnext webserver when the IP is assigned via DHCP.

We found a workaround using the free service Duckdns :

There is a variety of ways to login, for instance via Google account. You get a token and aftewards you can select a domain like : http://

The service has an API that can be used from Plcnext Engineer.

With the help of FB PBCL_SysNetwork ( part of PlcnextBase library ), you can readout the IP that has been assigned to the plc by the DHCP server.

Using again a FB from the same library, PBCL_SysLinuxShell, this command can be sent to Duckdns:

curl -s --connect-timeout 5 -m 15 ">&ip=<your_local_ip>&verbose=true"

The trick is to update your host not with the public address of your router ( this is the normal use of this service ), but with you local address assigned by DHCP.

You have to type in a browser running in a pc in the local network. This browser will go to Duckdkns to resolve the IP and it will answer with the local IP.


The Makers Blog shows applications and user stories of community members that are not tested or reviewed by Phoenix Contact. Use them at your own risk.


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