Open5GS and ZMQ (gNB + UE) setup on separate machines

[ahmadhassandebugs]

Hi all,

I have a setup where Open5GS is running on one machine (M1) and ZMQ-based srsRAN gNB and srsUE on another machine (M2). Both machines are on the local network. I tested the setup and it seems to be working - srsUE is able to establish RRC connection with the core and it creates a tun tun_srsue inside the network namespace ue1. However, I cannot figure out how to configure routing on M2 so that srsUE can transmit/receive traffic to/from the Open5GS core running on M1. For clarity, here's the summary of the setup:

• M1
  • Open5GS built from source
• M2
  • srsRAN with ZMQ radio
  • srsUE with ZMQ radio

Note that I was able to successfully run this setup on a single machine after following ZeroMQ-based Setup tutorial.

I think if I can connect tun_srsue inside namespace ue1 to the root (by IP MASQUERADING and FORWARDING), it might solve the issue. Any kind of help/advice will be greatly appreciated.

Thank you!

[pgawlowicz]

Hi, does Open5gs listen on correct interface for ngap connection?
Could you share your configs?

[ahmadhassandebugs]

Yes, I believe NGAP listens for connections on the correct interface. Here are the configurations (attached in TXT format since github won't let me upload yaml files):

• sa_base.txt
• gnb_zmq.txt
• ue_zmq.txt

M1 Open5GS machine has IP address 10.182.50.31 while M2 (gNB and UE) has IP address 10.182.50.201.

Below is a screenshot of M2 terminal when I run the gNB and UE.

Thanks!

[pgawlowicz]

could you try this to set this parameter:

https://github.com/herlesupreeth/docker_open5gs/blob/8b2f5c9211f37fc9a0d8b1256eec845953a42bb6/upf/upf.yaml#L18C2-L18C38
I think you should set:

upf:
...
    gtpu:
      server:
        - address: 127.0.0.4
          advertise: 10.182.50.31

[ahmadhassandebugs]

I tried it and it's still the same issue. Could you explain why this might have solved the issue?

Please note that I am not using the dockerized open5gs. I built it from scratch and am running the 5gc binary.

I think the problem is not because of some Open5GS or srsRAN (mis)configuration, but due to missing routing configuration on M2. This is why I cannot use tun_srsue inside ue1 namespace to ping the root (10.182.50.201). I probably need to find a way to connect tun_srsue to the root interface eno1 (10.182.50.201).

If it is still confusing, I can provide more step-by-step details about the setup and network configuration (ip a and route -n for root and ue1 namespace).

[pgawlowicz]

ah wait, the UE gets the IP assigned.
Then please try to add a default route to the UE netns:

sudo ip netns exec ue1 ip route add default via 10.45.0.1 dev tun_srsue

[ahmadhassandebugs]

Yes, the IP gets assigned.

I have tried doing that before but it didn't work. Check the screenshot (bottom right tab) below for an overview of routing configurations. Inside ue1 namespace, I was not able to ping the gateway (10.45.0.1) or the root (10.182.50.201).

Thanks!

[pgawlowicz]

hmm, maybe some firewall rules? or ip forwarding?

[manasik2019]

I faced the same issue, it turns out that there is an iptables rule that drops packets from source 10.45.0.0/16, I initially configured it following open5gs guides for building from sources as below:

This solves it:

sudo iptables -L -n -v # list all rules
sudo iptables -D INPUT -s 10.45.0.0/16 -j DROP # remove the one causing issues

[ahmadhassandebugs]

I never configured these security rules on my setup so that shouldn't be an issue.

Regardless, I set up the same setup with docker_open5gs repository after some struggle so all good :)

[Gyrusk]

@ahmadhassandebugs were you able to figure it out?