N3IWUE ping failure (0% success) after PDU session, using Free5GC default config on VirtualBox

Hi everyone,

I’m setting up Free5GC Core and N3IWUE using the official guide, with everything running on VirtualBox using the default configuration from the manual.

Setup:

free5gc core and n3iwue in separate VMs

cloned from official repo, branch v4.0.1

followed instructions from https://free5gc.org/guide/n3iwue-installation

Interface: UPF connected to data network via enp0s8

When I run:

cd ~/n3iwue
./run.sh

I see the following logs indicating GRE tunnels were created and PDU session established:

2025-06-18T14:39:22Z [INFO][N3UE][APP] New GRE Tunnel, Key Field: [0x1000000], IfaceName: [gretun-id-2-1]
2025-06-18T14:39:22Z [INFO][N3UE][APP] New GRE Tunnel, Key Field: [0x2000000], IfaceName: [gretun-id-2-2]
2025-06-18T14:39:22Z [INFO][N3UE][NAS] Add route: QFI[1] remote address[{Address:0.0.0.0 Mask:00000000}]
2025-06-18T14:39:22Z [INFO][N3UE][NAS] Add route: QFI[2] remote address[{Address:1.1.1.1 Mask:ffffffff}]
2025-06-18T14:39:22Z [INFO][N3UE][APP] PduSession Created
2025-06-18T14:39:36Z [INFO][N3UE][APP] — 9.9.9.9 ping statistics —
2025-06-18T14:39:36Z [INFO][N3UE][APP] 5 packets transmitted, 0 packets received, 100% packet loss
2025-06-18T14:39:37Z [ERRO][N3UE][APP] ping fail : Ping Failed

:white_check_mark: What I’ve already tried:
Enabled IP forwarding:

sudo sysctl -w net.ipv4.ip_forward=1
Applied NAT on the data network interface:
sudo iptables -t nat -A POSTROUTING -o enp0s8 -j MASQUERADE
Disabled the firewall:
sudo systemctl stop ufw
sudo systemctl disable ufw
:question:Issue:
Everything sets up without crashing

GRE tunnels get created

Routes are configured

But ICMP ping to 9.9.9.9 fails (100% loss)

:jigsaw: Questions:
Where might packets be getting lost? Is it UPF → DN, or DN → UPF?

Do I need additional configuration for UPF’s gtp5g or GRE handling?

Are there known MTU/GRE/GTP pitfalls with the default N3IWUE setup?

Let me know what logs or traces I can share to help further (e.g. tcpdump on UPF/N3IWUE, PDU session config, etc.). Thanks in advance!

Hi @An0107,

I set up free5GC and N3IWUE, and everything is working fine.
However, I noticed that my data network interface is set to enp0s3 (10.0.2.15) instead of enp0s8 (192.168.56.101). Note that the enp0s8 is the “Host-only network interface” created following the Creating and Configuring a free5GC VM user guide.

Perhaps changing your DN interface to a different network interface will solve the problem.