ULCL of free5GC SMF changed

[s5uishida]

Hi @louisroyer

According to this, the ULCL code of free5GC SMF has been changed.

As a result, NextMN-UPF's ULCL have not worked.

FYI.

[louisroyer]

Thank you very much for sharing this information with me, and for the issue reporting on Free5GC :)

If I understand correctly, this issue is now fixed in the SMF?

Have you tested the new version with NextMN-UPF yet? If it doesn't work, please let me know.

[s5uishida]

I updated free5GC as follows and built it.

git clone --recursive -j `nproc` https://github.com/free5gc/free5gc.git
cd ~/free5gc
git checkout main
git submodule sync
git submodule update --init --jobs `nproc`
git submodule foreach git checkout main
git submodule foreach git pull --jobs `nproc`

[louisroyer]

Hi @s5uishida,
I can reproduce on my side with the following setup:

  specificPath:
    - dest: 10.4.0.1/32
      path: [UPFI, UPFA1]
    - dest: 10.4.0.2/32
      path: [UPFI, UPFA2]

(my UE is 10.2.1.129)

PDR created by the latest version of the SMF are strange (see PCAP attached):

• In packet number 41, the source interface is Access, and the flow description is permit out ip from 10.4.0.1/32 to 10.2.1.129 : this is correct
• In packet number 53, the source interface is Access, and the flow description is permit out ip from 10.2.1.129 to 10.4.0.2/32 : this is not correct (source and destination in wrong order).

UpdateRANAndIUPFUpLink probably has the same bug that was fixed in EstablishULCL.

ULCL happens to work correctly with free5gc/go-upf, and I cant figure out by what miracle : with the current PFCP rules this PDR should never be matched ; there is probably another bug in free5gc/go-upf.

Can you attach me a PCAP on N4 interface to confirm this is the exact same issue? Or logs from NextMN-UPF (it displays current rules periodically).

[louisroyer]

I might have found why free5gc/go-upf still works with wrong rules:
When the source interface is Access, it swap source and destination to convert filter description in this way:
https://github.com/free5gc/go-upf/blob/922281ba58b6ca42d73be218671c8feae3658420/internal/forwarder/gtp5g.go#L182-L185
but here, the fd.Dir must also be reversed (out/in) to work correctly.

This means the wrongly created permit out ip from 10.2.1.129 to 10.4.0.2/32 matches, but permit out ip from 10.4.0.1/32 to 10.2.1.129 does not. But there is a third "default" rule without SDF Filter that is matched instead, that have an identical FAR.

I will test this and, if it works, send pull requests to Free5GC.

EDIT: there is no bug in free5gc/go-upf, and the inversion in modified pdr is not related (but still a bug). The direct cause is a mistake I made while patching.

Version 0.0.11 should work.

[s5uishida]

Hi @louisroyer

It worked fine with v0.0.11.

Thank you very much!

[s5uishida]

Hi @louisroyer

I found your PR for free5GC SMF, so I tried it.

As a result, ULCL worked fine.

Thank you very much for your efforts!