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3:49, EET
March 2, 2021
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Hi,
I have written a java program to test my connections to OPCUA server.
First, I used the endpoint
opcua:tcp://uademo.prosysopc.com:53530/OPCUA/SimulationServer?discovery=false
and it connects successfully.
Second, I used the endpoint
opcua:tcp://127.0.1.1:53530/OPCUA/SimulationServer?discovery=false
which is a local instance of the OPCUA simulation server, it gives me the below error.
Unable to discover URL:opc.tcp://127.0.1.1:53530/OPCUA/SimulationServer/discovery
Do I need to set any configuration in the local instance of simulation server software to make the discovery successful.
Kindly suggest.
Thanks. 
8:21, EET
Moderators
February 11, 2020
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Hello,
This might sound obvious and you might have already done this, but have you verified that your local Simulation Server binds itself to 127.0.1.1? You can check this in the Endpoints tab by setting Bind Addresses to Custom and then pressing Configure button to see which addresses the Server is binding itself to.
If Simulation Server does bind itself to 127.0.1.1, have you tried connecting to the local Simulation Server with another Client such Prosys OPC UA Browser?
Also, your URLs are a bit weird. You’re using “opcua:tcp” while the prefix in the specification is “opc.tcp”. I have not seen parameters like “discovery=false” being appended to the address before either. Are you using the Prosys OPC UA SDK for Java to develop your Client with some customized address handling or something else?
8:44, EET
April 3, 2012
Offline
Hi
Actually, that is sort of a known issue. We wont bind to 127.0.1.1, only to 127.0.0.1, technically this happens is the OS (Ubuntu seems to do this) for some reason binds the local hostname to 127.0.1.1 when one could sort of assume it would be 127.0.0.1. Thus please use 127.0.0.1, that should work, let us know if not.
Eventually we should instead be listening to 0.0.0.0 by default, that should catch connection attempts to 127.0.1.1, but basically otherwise it is impossible (as far as I know) to “bind to all local addresses”.
9:36, EET
March 2, 2021
Offline
Hi,
Thanks for your reply and Yes – I am using Ubuntu OS. The solution recommended above (bind to 127.0.0.1) fixed the issue. Thanks again. .
22:22, EEST
July 26, 2021
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Bjarne Boström said
HiActually, that is sort of a known issue. We wont bind to 127.0.1.1, only to 127.0.0.1, technically this happens is the OS (Ubuntu seems to do this) for some reason binds the local hostname to 127.0.1.1 when one could sort of assume it would be 127.0.0.1. Thus please use 127.0.0.1, that should work, let us know if not.
Eventually we should instead be listening to 0.0.0.0 by default, that should catch connection attempts to 127.0.1.1, but basically otherwise it is impossible (as far as I know) to “bind to all local addresses”. Â
You may not need to bind to all loopback addresses, however it would be helpful if it binds to the address that the hostname resolves to, for Ubuntu for whatever reason it is 127.0.1.1.
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