Build a Software gNB based on free5GC - Need some clarification on config


Hi Folks,

I am currently trying to build a very simple Software gNB ( based on your code and the test scripts provided (it seems they are only intended for an All in One deployment on the same host).
My use case is to launch multiple gNB individually on different hosts to simulate UEs which could establish multiple PDU sessions with various UPFs.

But I have some trouble understanding the test scripts and some configuration files which raises some questions:

  • In the ‘smfcfg.test.yaml’ and in the, the IPv4 of the SMF N4 interface is set to and it seems to also be the IPv4 of the simulated gNB GTP-U tunnel Endpoint, is it done on purpose and could it be changed ?

  • Again in the same file, there is the an_ip for the RAN under the userplane_information section, it is set to and there is also a for the UPF up_resource_ip. How are used those IP internally ? (I’ve already read the wiki configuration and SMF config pages but still, I haven’t found out when running the tests how they are used).

  • In the uerouting.yaml used by the SMF, the AN field of each UE is set to the UPF GTP-U Endpoint IPv4, is it normal and is this field related to the an_ipof the smfcfg.yaml ?

Again thank you for your work on this free Standalone version of the 5G CN.


  1. N4 is not necessary putting on That’s because our network setting as below.

  2. an_ip is not using in this version of smf

  3. ®AN will send GTPU to upf. But because now the an_ip is not using for SMF, it is not necessary to be same.

Thank you for the answer