Connectivity in Multi UPF scenario



I’m trying to replicate the Multi UPF scenario posted on free5GC’s YouTube channel.

The IMS slice, PSA-UPF1 and UE2 are working fine and the UE can reach the internet.

However, I’m facing an unexplained connectivity issue with UE1, where it’s not receiving reply from neither the internet nor the MEC. At the same time, I’m able to capture the ICMP replies on both i-UPF and UPF2, and a “hw csum failure” on i-UPF in the case of intranet ping (all attached).

I have verified the configs multiple times, IP forwarding, NAT, Firewall… I have also tried turning off checksum offloading. What else could cause such problem?

Environment: free5GC 3.1.1, gtp5g 0.5.4, Ubuntu 20.04 (Kernel 5.4.0-120-generic), UERANSIM 3.2.6

i-upf.pcap (888 Bytes) psa-upf2.pcap (824 Bytes)

Hi @Hadi,
I use the environment you mentioned.
I can ping and via uesimtun0 like youtube video.


But I encountered the same situation about “hw csum failure” on i-UPF like you, so I think this error is not the main problem.

In the i-UPF.pcap you uploaded, we can see the ICMP reply which means i-UPF had received the reply.
Could you check whether the interface in i-UPF transport reply packet and whether the interface in UERANSIM receive reply packet?

Can you tell me the meaning of i-UPF and whether I can deploy it later? I only use two SMFs and two PSA-UPFs to successfully implement two slices.

Hi @xiaobinggan-zmh,
As far as I know, I-UPF means Intermediate UPF which can be used to support redundant transmission on N3/N9 interfaces and make UE connect to core network via I-UPF in access network.
You can check the description in TS23.501 R16
You can of course deploy the I-UPF whenever you want and design NFs network topology by yourself on the basis of free5GC.
The related work and video tutorial in free5GC: Environment setup of multiple SMF, DNN, and UPF (including ULCL) in

@SymbolWu I have another question I want to ask you, that is, I can access the HTML on MEC, but I can’t access the MP4 video, do you know what configuration can be used to solve this?