Uesd UERANSIM test Stage 3.0.4 ULCL Fail

Hi all,
we are testing the free5gc 3.0.4 ULCL architecture and used the kubernetes cluster

cluster env:
kubernetes v1.18.5 (in single node)
docker 20.10.6

In our test we used the UERANSIM gNodeB & UE to connect free5gc
the test tool like ping / httperf / curl are normal work
but when we testing the iperf3 and scp file transport
it cant access the UPF backend service (will fill the mtu)
so we change the UE side tunneling interface mtu
when we change it lower to TCP 472 && UDP 496
the UE can access the external service.

Is this is the gtp5g kernel module issue
or the ULCL archicture have some problem with MTU Size limit

By the way, In our testing the single UPF architecture didnt have this problem.

I also use K8S for deployment, may I ask if you have solved this problem.

Hi @ZhengSheng0524,
Could you try to set the TCP max segment size in bytes by using:sudo iptables -A FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1400 ?

We have previously encountered a packet size that was too large and was dropped.
Hope this solution can help you.