SMF Assign IP from Wrong Subnet When Selecting UPF based on TAC

[Esawi]

Open5GS Release, Revision, or Tag

v2.6.4

Steps to reproduce

Please need some support, I am wondering if I am doing something wrong there.

• Using Two UPFs.
• The SMF configured to select the UPF based on TAC. As below part from the SMF yaml:

upf:
    pfcp:
      - addr: 127.0.0.7
        tac: 1
      - addr: 127.0.0.117
        tac: 2

• Using two cells with different TAC.

Logs

No response

Expected behaviour

UE to connect to:

• UPF1 and get an IP on the 10.45.0.0/16 range when connecting to a cell with TAC1
• UPF2 and get an IP on the 10.46.0.0/16 range when connecting to a cell with TAC2

Observed Behaviour

• The UE when connected to the cell with TAC 1 will get an IP on the 10.45.0.0/16 range (corresponding to the first UPF) and be able to ping the UPF. (the UPF IP in the PDUSessionResourcesSetupRequest is correct)
• When connected to the cell with TAC 2, the RAN will receive the correct UPF IP of UPF2 on the PDUSessionResourcesSetupRequest, but the UE would be assigned an IP on the 10.45.0.0/16 range still. (not the 10.46.0.1). and the UE won't be able to ping the UPF correctly.

Traces, Configs and Logs:
20230829 - TestRun01.zip

eNodeB/gNodeB

No response

UE Models and versions

No response

[Esawi]

I should add, this is working fine if the DNN is used to pick the UPF.

[acetcom]

@Esawi

SMF only supports UE IP allocation per DNN. TAC, CELL_ID, etc. are not supported.

Please let me know if you have any other questions.

Thanks a lot!
Sukchan

[Esawi]

Thank you very much @acetcom , So with one SMF only DNN is possible.

• Can I use two SMFs each for a different TAC?
• Or load balance UEs on two SMF-UPF pair?

[acetcom]

@Esawi

Except for DNNs, SMF-UPF pairs should be used. You can implement UE load balancing by setting a different TAC for each of the two SMFs in smf.info and attaching a UPF to each SMF.

Connecting two UPFs, each with different TACs, to the same SMF you initially configured is not supported. This is because SMF allocates the UE Pool, but it is not implemented to allocate a different UE Pool for each TAC.

If you think this feature is necessary, please present it persuasively. Otherwise, this feature will remain as is.

Thanks a lot!
Sukchan

[Esawi]

Hi @acetcom ,

Thank you very much, I have been trying to use two SMF-UPF pairs with different TACs using smf.info, but I think perhaps I am still missing something.

Could you please take a look at below.
In this test run the UE is connecting to a cell with TAC 2 but it keeps using SMF1-UPF1 (10.45.0.0/16 range) instead of SMF2-UPF2 as configured.

File include, trace, configs and logs:
20230912_test_run.zip

On SMF2:

    info:
      - s_nssai:
          - sst: 1
            dnn: [internet, internet2, ims]
          - sst: 2
            dnn: [internet, internet2, ims]
        tai:
          - plmn_id:
              mcc: 999
              mnc: 99
            tac: 2

[s5uishida]

Hi @Esawi

For your reference, a very simple configuration example to select an SMF-UPF pair using TAC is as follows.
The version used in the article is a little old, but it also works fine with the latest Open5GS.

https://github.com/s5uishida/open5gs_5gc_ueransim_nearby_upf_sample_config

[Esawi]

Thank you @s5uishida ,

Indeed I used that article as a reference when configured the core, but I am still seeing that only SMF1-UPF1 is used not matter which TAC I use.

[acetcom]

@Esawi and @s5uishida

I confirm that it is currently working well on the main branch and v2.6.4.

[Esawi]

Hi @acetcom ,

Please need your support to check the attached config and logs, I am not sure if I am missing anything , but regardless of the TAC used the same SMF-UPF pair is being used.

Attached test run and configs using UERANSIM

20230925_testrun_01.zip

[acetcom]

@Esawi

See below.
https://github.com/open5gs/open5gs/wiki/Support-policy

Sorry for not help this!
Sukchan

[Esawi]

@acetcom Thank you for the support.
I will try to double check the configs again.

[acetcom]

@Esawi

When finding an SMF in the NRF discovery process, TAI should be used as a parameter if needed. However, AMF is connected to NRF via SCP and discovering different SMFs by TAI does not work properly.

Until the bug is fixed, this problem can be resolved by connecting the AMF directly to the NRF as below.

$ diff --git a/configs/open5gs/amf.yaml.in b/configs/open5gs/amf.yaml.in
index b022552db..d23fb267d 100644
--- a/configs/open5gs/amf.yaml.in
+++ b/configs/open5gs/amf.yaml.in
@@ -567,10 +567,10 @@ amf:
 #          l_linger: 10
 #
 #
-scp:
-    sbi:
-      - addr: 127.0.1.10
-        port: 7777
+#scp:
+#    sbi:
+#      - addr: 127.0.1.10
+#        port: 7777
 
 #
 #  <SBI Client>>
@@ -631,12 +631,10 @@ scp:
 #          l_onoff: true
 #          l_linger: 10
 #
-#nrf:
-#    sbi:
-#      - addr:
-#          - 127.0.0.10
-#          - ::1
-#        port: 7777
+nrf:
+    sbi:
+      - addr: 127.0.0.10
+        port: 7777
 
 #
 #  o Disable use of IPv4 addresses (only IPv6)

For other NFs, it is okay to connect SCP. Therefore, you only need to change the AMF settings as above.

I thought it was not an Open5GS bug, so there seemed to be confusion.
Sorry for this, and I'll let you know once this bug is fixed.

Please let me know if you have any other questions.

Thank you so much for raising this issue.
Sukchan

[Esawi]

@acetcom
Thank you very much for the support. Using the NRF is giving the expected behavior.

[acetcom]

@Esawi

I've fixed this issue in the main branch. Now you will be able to operate normally even when using SCP.

Thank you so much for raising this issue.
Sukchan

[Esawi]

Thank you @acetcom , using either NRF or SCP is working as it should with v2.7.0