Content for TS 33.501 Word version: 18.4.0

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11.1 EAP based secondary authentication by an external DN-AAA server 11.1.1 General 11.1.2 Authentication 11.1.3 Re-Authentication 11.1.4 Secondary authentication and authorization revocation
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11 Security procedures between UE and external data networks via the 5G Network p. 160

11.1 EAP based secondary authentication by an external DN-AAA server p. 160

11.1.1 General p. 160

This subclause specifies support for optional to use secondary authentication between the UE and an external data network (DN).

The EAP framework specified in RFC 3748 shall be used for authentication between the UE and a DN-AAA server in the external data network. The SMF shall perform the role of the EAP Authenticator. In the non-roaming scenario, the SMF shall perform the role of EAP Authenticator. And In the local break out scenario, the V-SMF of visited nework shall perform the role of EAP Authenticator. In the Home Routed deployment scenario, the H-SMF shall perform the role of the EAP Authenticator and the V-SMF shall transport the EAP messages exchanged between the UE and H-SMF. It shall rely on the external DN-AAA server to authenticate and authorize the UE's request for the establishment of PDU sessions.

Between the UE and the SMF, EAP messages shall be sent in the SM NAS message. This message is received at the AMF over N1 and delivered to the SMF over N11 using either the Nsmf_PDUSession_CreateSMContext service operation or the Nsmf_PDUSession_Update SM Context service operation, as specified in TS 23.502. The SMF that takes the role of the EAP authenticator communicates with the external DN-AAA over N4 and N6 via the UPF.

The SMF invokes the Namf_Communication_N1N2MessageTransfer service operation to transfer the N1 NAS message containing the EAP message, towards the UE via the AMF.

Following clauses describe the procedures for initial Authentication and Re-Authentication with the external DN-AAA server.

11.1.2 Authentication p. 161

Reproduction of 3GPP TS 33.501, Fig. 11.1.2-1: Initial EAP Authentication with an external AAA server

Figure 11.1.2-1: Initial EAP Authentication with an external AAA server

This procedure concerns both roaming and non-roaming scenarios. In the non-roaming case, the V-SMF is not involved. In the HR roaming case, the V-SMF shall proxy the signalling between the AMF in the VPLMN and the H-SMF in the HPLMN. In the LBO roaming case, only one SMF in VPLMN is involved.

The following procedure is based on subclauses 4.2.2.2.2, 4.3.2.2.1 and 4.3.2.3 in TS 23.502.

Step 1-3.

The NG-UE registers with the network performing primary authentication with the AUSF/ARPF based on its network access credentials and establishes a NAS security context with the AMF.

Step 4.

The UE initiates establishment of a new PDU Session by sending a NAS message containing a PDU Session Establishment Request within the N1 SM container, slice information (identified by S-NSSAI) , PDU session ID and the PDN it would like to connect to (identified by DNN).

The PDU Session Establishment Request may contain SM PDU DN Request Container IE containing information for the PDU session authorization by the external DN.

Step 5a.

The AMF selects a V-SMF and sends either Nsmf_PDUSession_CreateSMContext Request or Nsmf_PDUSession_UpdateSMContext Request with the N1 SM container as one of its payload. It also forwards SUPI PDU Session ID, the received S-NSSAI, and the DNN.

Step 5b.

The V-SMF sends an Nsmf_PDUSession_CreateSMContext Response or Nsmf_PDUSession_UpdateSMContext Response correspondingly to the AMF.

In case of a single SMF being involved in the PDU session setup, e.g. non-roaming or local breakout, that single SMF takes the role of both V-SMF and H-SMF. In this case, steps 6 and 17 are skipped.

Step 6.

The V-SMF sends an Nsmf_PDUSession_Create Request to the H-SMF.

Step 7.

The H-SMF obtains subscription data from the UDM for the given SUPI obtained from the AMF in step 5. The SMF checks the subscription data whether the secondary authentication is required and whether the UE request is allowed according to the user subscription and local policies. If not allowed, the H-SMF will reject UE's request via SM-NAS signalling and skip rest of the procedure. If secondary authentication is required, the SMF may also check whether the UE has been authenticated and/or authorized by the same DN, as indicated DNN in step 5, or the same AAA server in a previous PDU session establishment. The SMF may skip steps 8 to 15 if positive.

Step 8.

The H-SMF shall trigger EAP Authentication to obtain authorization from an external DN-AAA server. If there is no existing N4 session, the H-SMF selects a UPF and establishes an N4 Session with it. The H-SMF notifies the DN-AAA server with the GPSI, if available, and the IP address(es) of the UE allocated to the PDU Session if the PDU session is of IP PDU type or the MAC address if the PDU session is of Ethernet PDU type.

Step 9.

The H-SMF may send an EAP Request/Identity message to the UE.

Step 10.

The UE may send an EAP Response/Identity message contained within t a NAS message. The DN-specific identity shall comply with Network Access Identifier (NAI) format.

To avoid the additional round-trip in steps 9 and 10, the secondary authentication DN-specific identity may be sent by the UE in step 4. In this case, H-SMF forms an EAP Response/Identity message that contains the identity.

Step 11.

If there is no existing N4 session, the H-SMF selects a UPF and establishes an N4 Session with it.

Step 12.

The DN-specific identity, if provided by the UE, is forwarded to the UPF. The H-SMF identifies the DN AAA server based on the DN-specific identity provided by the UE and on local configuration.

The UPF shall forward the DN-specific identity within an EAP Response/Identity message to the DN AAA Server.

Step 13.

The DN AAA server and the UE shall exchange EAP messages, as required by the EAP method. In addition, it may send additional authorization information as defined in clause 5.6.6 of TS 23.501.

Step 14.

After the successful completion of the authentication procedure, DN AAA server shall send EAP Success message to the H-SMF.

Step 15.

This completes the authentication procedure at the SMF. The SMF may save the DN-specific ID and DNN (or DN's AAA server ID if available) in a list for successful authentication/authorization between UE and an SMF. Alternatively, the SMF may update the list in UDM.

If the authorization is successful, PDU Session Establishment proceeds further starting at step 7a of Figure 4.3.2.2.1-1 in TS 23.502.

Step 16a-16b.

The SMF initiates a N4 Session Modification procedure with the selected UPF as in steps 10a and 10b of Figure 4.3.2.2.1-1 in TS 23.502.

Step 17.

The H-SMF sends an Nsmf_PDUSession_Create Response to the V-SMF. This message shall include EAP Success to be sent to the UE to V-SMF.

Step 18.

The V-SMF sends Namf_Communication_N1N2MessageTransfer to the AMF as in step 11 of Figure 4.3.2.2.1-1 in TS 23.502. This message shall include EAP Success to be sent to the UE within the NAS SM PDU Session Establishment Accept message.

Step 19.

The AMF forwards NAS SM PDU Session Establishment Accept message along with EAP Success to the UE as described in steps 12 and step 13 of Figure 4.3.2.2.1-1 in TS 23.502.

The UE-requested PDU Session Establishment authentication/authorization by a DN-AAA server proceeds further as described in subclause 4.3.2.3 in TS 23.502.

11.1.3 Re-Authentication p. 164

Reproduction of 3GPP TS 33.501, Fig. 11.1.3-1: EAP Re-Authentication with an external AAA server

Figure 11.1.3-1: EAP Re-Authentication with an external AAA server

This procedure concerns both roaming and non-roaming scenarios. In the non-roaming and LBO roaming cases, only one SMF is involved. In the HR roaming case, the V-SMF shall proxy the signalling between the AMF in the VPLMN and the H-SMF in the HPLMN.

Step 1-3.

Secondary Authentication has been established according to procedures specified in clause 11.1.2, Initial EAP Authentication with an external AAA server.

Secondary Re-authentication may either be initiated by SMF or the external DN/AAA server. If Re-authentication is initiated by SMF, the procedure proceeds with step 4 (skipping steps 4a and 4b). If Re-authentication is initiated by the external DN/AAA server, the procedure proceeds with the alternative steps 4a and 4b.

Step 4.

The SMF decides to initiate Secondary Re-Authentication.

Step 4a.

The DN AAA server decides to initiate Secondary Re-Authentication.

Step 4b.

The DN AAA shall send a Secondary Re-Authentication request to UPF, and the UPF forwards it to SMF. The Secondary Re-authentication request contains the GPSI, if available, and the IP/MAC address of the UE allocated to the PDU Session and the MAC address if the PDU session is of Ethernet PDU type.

Step 6.

The UE shall respond with an EAP Response/Identity message (with Fast-Reauth Identity).

Step 7.

The SMF forwards the EAP Response/Identity to UPF, selected during initial authentication, over N4 interface.

This establishes an end-to-end connection between the SMF and the external DN-AAA server for EAP exchange.

Step 8.

The UPF shall forward the EAP Response/Identity message to the DN AAA Server.

Step 9.

The DN AAA server and the UE shall exchange EAP messages as required by the EAP method.

Step 10.

After the completion of the authentication procedure, DN AAA server either sends EAP Success or EAP Failure message to the SMF.

Step 11.

This completes the Re-authentication procedure at the SMF.

Step 12-13.

If the authentication is successful, EAP-Success shall be sent to UE.

Step 12-14.

If authentication is not successful, the SMF notifies failure to UPF. Upon completion of a N4 Session Modification procedure with the selected UPF, SMF sends EAP-Failure to UE via AMF.

11.1.4 Secondary authentication and authorization revocation p. 165

At any time, a DN-AAA server may revoke the authentication and authorization for a PDU Session and according to the request from the DN-AAA server, the SMF may release the PDU Session as specified in sub-clause 4.3.4 of TS 23.502.