Free5gc GTP Payload doesn't contain PDU session container in UL and DL

Simran · May 12, 2021, 1:52am

Hi All,

Recently I found out that the GTP payload is not forwarded with the external PDU Session container that is required to verify the PDU Session ID and QFI in the user plane packets. Otherwise it may lead to conflicts when different UE with same DL-TEID are attached with free5gc.
Has anyone came across the same ? Please discuss your points.
Thank you,
free5gc_ping_packets.pcapng (3.8 MB)

muthuramanecs03g · May 15, 2021, 4:02pm

Hi Simran,

Did you validate the QER entry in the gtp5g kernel module?

Regards,
Muthuraman

free5GC · May 16, 2021, 8:47am

@Simran

This issue was already fixed.
Please refer to this:

github.com/free5gc/free5gc

[Feat] UPF verification of user traffic with QFI in the GTP-U extension header

opened 01:38PM - 28 Aug 20 UTC

closed 02:38PM - 19 Feb 21 UTC

am677

UPF

## Issue Description ### What's the version are you using v3.0.3 ### Is y…our feature request related to a problem? Please describe. UPF can not handle the user traffic properly over GTP-U with the extension header properly. > WARN[2020-04-17T20:05:19+09:00] c/upf/src/up/up_path.c:119 GtpHandler() This type[255] of GTPv1 header does not implement yet UPF=Util (UE->)AN->UPF user traffic ![extension_header](https://user-images.githubusercontent.com/66290148/91566776-1c1cf680-e97f-11ea-9ceb-9df9c8c55bfb.png) ### Describe the solution you'd like UPF should handle user traffic over the GTP-U with QFI in the extension header properly. See 3GPP TS23.501 5.7.1.7 UL Traffic > UPF verifies whether QFIs in the UL PDUs are aligned with the QoS Rules provided to the UE or implicitly derived by the UE in the case of Reflective QoS). ### Describe alternatives/workarounds you've considered None. ### Additional context 3GPP TS23.501 5.7.1.7 UL Traffic > (R)AN transmits the PDUs over N3 tunnel towards UPF. When passing an UL packet from (R)AN to CN, the (R)AN includes the QFI value, in the encapsulation header of the UL PDU, and selects the N3 tunnel. 8.3.1 User Plane Protocol Stack for a PDU Session -> GPRS Tunnelling Protocol for the user plane (GTP-U): > GTP shall encapsulate all end user PDUs. It provides encapsulation on a per PDU Session level. This layer carries also the marking associated with a QoS Flow defined in clause 5.7. #### Log [gtp.zip](https://github.com/free5gc/free5gc/files/5142322/gtp.zip) #### Related issue #100 I suppose that the Q/A topic below is related to this issue. https://forum.free5gc.org/t/gtp-data-not-forwarded-by-upf/74/4 ## Issue Template Checklist ### Would you be willing to resolve this issue by submitting a Pull Request? - [ ] Yes, I have the time and I know how to start. - [ ] Yes, I have the time but I don't know how to start, I would need guidance. - [x] No, I don't have the time, although I believe I could do it if I had the time... - [ ] No, I don't have the time and I wouldn't even know how to start.

Simran · May 17, 2021, 4:26am

Hi @muthuramanecs03g,

Thanks for the quick response.
The UPF is handling the packets ( that have PDU Session extension header) correctly. But the DL packets doesn’t have the PDU Session container.
Is there any flag or hardcode something that I need to change at gtp5g kernal module for QER entry ?

Thank You
Simran

muthuramanecs03g · May 17, 2021, 5:01am

Hi @Simran,

In gtp5g, you can refer to the function gtp5g_push_header() whether the DL packet encapsulates the extension header or not.

I suspect, there is some problem with your DL PDR rule action is not set as FORWARD.

Simran · May 17, 2021, 5:47am

Hi @muthuramanecs03g,
I checked the same with UERANSIM if free5gc is sending PDU session container header in DL packets.
@free5GC Can you please comment something here ? ueransim_packets.pcapng (4.3 KB)
I have attached the pcap for your reference.

Thank you.

muthuramanecs03g · May 17, 2021, 6:07am

Hi @Simran,

Could you please give me the SMF and UPF PFCP packet trace?

Simran · May 17, 2021, 6:32am

Hi @muthuramanecs03g,

Sure, PFA logs for UERANSIM. I am not sure if they can help you.
I tried setting SMF and PFCP logs to different levels, but it seems only info level logs are present here. log_free5gc.tar (110 KB)

Thanks.

muthuramanecs03g · May 17, 2021, 1:11pm

Hi @Simran,

The log message only confirm the what message transaction in between SMF and UPF, doesn’t show us the entire payload of that transaction.

I need a wireshark capture of interface local interface since your SMF and UPF ip addresses 127.0.0.1 and 127.0.0.8 respectively.

time=“2021-05-17T11:55:52+05:30” level=info msg="[PFCP] Handle PFCP session establishment request" category=Util component=UPF
time=“2021-05-17T11:55:52+05:30” level=info msg="[PFCP] Session Establishment Response" category=Util component=UPF
time=“2021-05-17T11:55:52+05:30” level=info msg=“In HandlePfcpSessionEstablishmentResponse” category=PFCP component=SMF
time=“2021-05-17T11:55:52+05:30” level=info msg=“Remove Request Transaction [2]\n” category=PFCP component=LIB
time=“2021-05-17T11:55:52+05:30” level=info msg="[PFCP] Handle PFCP session modification request" category=Util component=UPF
time=“2021-05-17T11:55:52+05:30” level=info msg="[PFCP] Session Modification Response" category=Util component=UPF
time=“2021-05-17T11:55:52+05:30” level=info msg=“In HandlePfcpSessionModificationResponse” category=PFCP component=SMF
time=“2021-05-17T11:55:52+05:30” level=info msg="[SMF] PFCP Modification Resonse Accept" category=PduSess component=SMF
time=“2021-05-17T11:55:52+05:30” level=info msg=“PFCP Session Modification Success[1]\n” category=PFCP component=SMF

Simran · May 18, 2021, 11:08am

Hi @muthuramanecs03g,
I am not able to upload the capture due to limit on file size.

muthuramanecs03g · May 18, 2021, 12:39pm

Hi @Simran,

You can upload it into google drive and share with me ([email protected])

Simran · May 20, 2021, 10:04am

Hi @muthuramanecs03g,

I have shared the Capture with you over email. Please let me know if you find any progress on this.

Thanks.

muthuramanecs03g · May 30, 2021, 2:28am

Hi @Simran,

There is no QER in PFCP Session Establishment/Modification request. I can see GTP-U carry an extension header but UPF didn’t send a response with the extension header due to no availability of QER.

I think the problem with gNB NGAP IEs, I will get back to you the reason once I got information from the SMF owner.

muthuramanecs03g · May 30, 2021, 12:24pm

Hi @Simran,

May I know your free5GC source code version? like latest or different version

Simran · May 31, 2021, 4:16am

Hi @muthuramanecs03g,
Please find the latest capture after cloning gtp5g and libgtp5gnl from free5gc git repo, Now at PFCP establishment request there is QER entry but it is not present in PFCP session modification request.

Let me know if anything needs to be changed in NGAP IEs, This capture also has the ngap msgs.
I am using the latest version of free5gc.
cap_31May_pfcp.pcapng (3.8 KB)
Tank you.