Patent Description:
For DNS procedures, an EDNS Client Subnet (ECS) option has been defined. The ECS option is an extension that enables DNS query and response to also contain information on a subnet where a respective entity is hosted (see [C]). In [A] an "EDNS Client Subnet" option is mentioned as one functionality that an EADSF can offer. In other words, it is possible that in a 3GPP network this ECS option is used.

<NPL>, describes an Extension Mechanisms for DNS option that is in active use to carry information about the network that originated a DNS query and the network for which the subsequent response can be cached.

<NPL>), describes that an SMF configures an EASDF DNS handling rules regarding and ECS option.

<NPL>), describes interaction between SMF and EASDF for the EASDF to get UPF information, DNN, DNAI and UE location.

<CIT> describes that an SMF obtains at least one group of first incidence relation, the first incidence relation being a corresponding relation between DNS processing information identification information and DNS processing information, the SMF discovers at least one group of first association relationships of an EASDF for PDU sessions of a plurality of terminal devices from an edge application server, and sends a corresponding first message corresponding to the first PDU session to the EASDF, the first message comprising first identification information, the first identification information being DNS processing information identification information corresponding to the first PDU session. Finally, the EASDF receives the first association relationship and the first message, and determines DNS processing information corresponding to the first PDU session according to the first association relationship and the first identification information.

The invention relates to a first network entity being an EASDF.

Further, the invention relates to a second network entity being an SMF.

According to at least some example embodiments, the communication network comprises a <NUM> system, but is not limited thereto. The communication network may comprise also future communication systems. For PDU Session with Session Breakout connectivity model, based on UE subscription (e.g. DNN) and/or operator's configuration, a DNS Query sent by UE is handled by the first network entity, or by a local or central DNS resolver/server. According to the invention, the DNS Query sent by UE carries an EDNS Client Subnet option in the DNS message (which is also referred to in the following as "first message").

According to at least some example embodiments, the first functionality of the first network entity comprises handling DNS messages according to an instruction from the second network entity, the first functionality including:.

The first network entity may further include one or more of the following functionalities:.

According to at least some example embodiments, the first network entity has direct user plane connectivity (i.e. without any NAT) with PSA UPF over N6 interface for transmission of DNS signaling exchanged with the UE. According to at least some example embodiments, the deployment of a NAT between EASDF and PSA UPF is not supported. According to at least some example embodiments, multiple EASDF instances are deployed within a PLMN. According to at least some example embodiments, interactions between 5GC NF(s) and the EASDF take place within a PLMN.

Below, two practical scenarios are indicated:.

According the invention, the first network entity replaces the Client Subnet Option (also referred to in the following as "third information") in the DNS query sent by the UE with a Client Subnet Option (also referred to in the following as "second information") in the DNS Query as associated with UPF PSA / DNAI pre-selected by the second network entity, and removes the Client Subnet Option associated with the pre-selected UPF PSA / DNAI from a DNS Response received from a DNS authoritative server.

According to the invention, the first network entity re-inserts the original Client Subnet Option, i.e. the one received in the DNS query message from UE, in place of the DNS response possibly received in the DNS Query.

According to at least some example embodiments, the first network entity is instructed by the second network entity to perform these actions. Alternatively, according to at least some example embodiments, the first network entity performs these actions based on local configuration available at the first network entity.

According to the invention, the first network entity comprises the EASDF and is instructed by the SMF functioning as the second network entity.

According to at least some example embodiments, the second network entity instructs the first network entity to respond the DNS query which carries the Client Subnet option with a response "REFUSED". For example, according to at least some example embodiments, the user plane is instructed to report the client subnet option to the control plane and the control plane forwards the REFUSED response via the user plane to the UE. Without EASDF or according to the prior art, if UE adds EDNS client subnet option in DNS Query, according to [C], DNS server in its DNS response to the UE also keeps this option in the DNS response.

In case the EASDF is added by the 5GC as DNS proxy (as specified in 3GPP Rel-<NUM>) then this DNS query from UE goes to EASDF first which, according to at least some example embodiments, replaces the EDNS client subnet option with another EDNS client subnet option e.g. as instructed by SMF to EASDF e.g. to better resolve DNS query to suite specific UPF deployment and UE location etc. This then gets resolved by DNS server, and the DNS server responds to EASDF with the EDNS client subnet information (EDNS client subnet option) as added/provided by the EASDF (and not the one provided by the UE). EDNS client subnet information from EASDF indicates some 5GC specific deployment information, e.g. PSA-UPF IP address in this case, which need not be revealed to the UE. To avoid this, according to at least some example embodiments, EASDF replaces back the EDNS client subnet information in the DNS response before sending to the UE to the one provided by the UE in the DNS query to the EASDF.

According to at least some example embodiments, the following problems are solved:.

Now reference is made to <FIG> showing a flowchart illustrating a process <NUM> according to at least some example embodiments.

According to the invention, process <NUM> is performed by the first network entity.

In step S101, a first message is received from a user equipment, the first message including at least first information regarding a domain name server query. Then, process <NUM> advances to step S103.

In step S103, in accordance with a first handling rule, the first message is processed by including second information regarding a subnet option into the first message, and the processed first message is forwarded to a domain name server, such as a DNS server. Then, process <NUM> advances to step S105.

For example, the subnet option enables the domain name server query and the response to also contain information on a subnet where a respective entity of the domain name server query is hosted. For example, the second information comprises core network specific deployment information.

In step S105, a second message is received from the domain name server, the second message including a response to the domain name server query and the second information. Then, process <NUM> advances to step S107.

In step S107, in accordance with a second handling rule, the second message is processed by replacing the second information, and the processed second message is forwarded to the user equipment. Then, process <NUM> ends.

In case of above indicated scenario a), according to at least some example embodiments, in step S107, the second information is omitted, and the second message from which the second information has been omitted is forwarded to the UE.

In case of above indicated scenario b), that is, in case the first message further includes third information regarding the subnet option, according to at least some example embodiments, in step S103, the third information in the first message is replaced by the second information, and the processed first message including the second information instead of the third information is forwarded to the domain name server. The second information is different from the third information. Further, according to at least some example embodiments, in step S107, the second information in the second message is replaced by the third information, and the processed second message including the third information instead of the second information is forwarded to the UE.

According to at least some example embodiments, the replacing the second information in step S107 comprises replacing the second information by fourth information regarding the subnet option, the fourth information being different from the second information. According to at least some example embodiments, the fourth information does not contain any network internal information.

According to at least some example embodiments, in case the first message includes the third information regarding the subnet option, the domain name server query is refused, e.g. in case of EAS discovery with local DNS server/resolver as defined in clause <NUM>. <NUM> of [A].

According to at least some example embodiments, the first and second handling rules are received from another network entity of the communication network, e.g. the second network entity.

According to at least some example embodiments, the first network entity is (pre-)configured with the first and second handling rules.

Now reference is made to <FIG> showing a flowchart illustrating a process <NUM> according to at least some example embodiments. According to the invention, process <NUM> is performed by the second network entity.

In step S201, a first handling rule of processing a first message from a user equipment is decided. This processing comprises including information regarding a subnet option into the first message. Then, process <NUM> advances to step S203.

In step S203, a second handling rule of processing a second message towards a user equipment is decided. This processing comprises removing the information regarding the subnet option from the second message. Then, process <NUM> advances to step S205.

In step S205, a domain name system update request including the first and second handling rules is sent to another network entity for exchanging domain name system messages from the user equipment, e.g. the first network entity.

In step S201, according to at least some example embodiments, the first handling rule is decided as follows:.

In step S203, according to at least some example embodiments, the second handling rule is decided as follows:.

In the following, further details of processes <NUM> and <NUM> will be described.

For the case that the UE DNS Query is to be handled by EASDF, the following applies.

NOTE <NUM>: The FQDN can be set to wildcard to indicate the default DNS Server (e.g. the C-DNS), for the case in which the DNS message should be forwarded to the default DNS Server.

NOTE <NUM>: The BaselineDNSPattern can be configured for a specific application with the related FQDN set in the detection template.

NOTE <NUM>: The definition of structure of Baseline DNS handling actions ID and Detection template ID is left to stage <NUM>. As an example, Baseline DNS handling action ID and Detection template ID could contain a concatenation of the SMF ID or SMF set Id and of SMF implementation selected information such as the DNAI or a sequence number. The EASDF is not meant to understand the structure of Baseline DNS handling actions ID and Detection template ID.

NOTE <NUM>: For DNS message type = Query, the UE IP address provided at DNS context creation (Neasdf_DNSContext_Create Request) is considered if not provided explicitly as part of the DNS message detection template.

NOTE <NUM>: DNS message Identifier is used by EASDF for matching between the message reported in the Neasdf_DNSContext_Notify and the corresponding DNS message handling rule included in.

NOTE <NUM>: With reporting-once indication, the DNS message detection template should contain the EAS IP address ranges corresponding to the same DNAI. Resetting the Reporting-once indication can be used by the SMF to allow reporting associated with a DNS handling rule when the SMF has removed the UL-CL/BP e.g. when the UE has moved out of the area associated with the current DNAI and thus insertion of a new UPF offloading capability can be considered.

NOTE <NUM>: The forwarding action can include either A or B.

NOTE 7A: Alternatively, according to at least some example embodiments, based on local configuration at the EASDF the EASDF may insert/replace the EDNS Client Subnet option, which was received in the DNS query message from UE and was removed by the EASDF from the DNS query.

When the EASDF forwards a DNS message (to the UE or towards a DNS server over N6), it uses its own address as the source address of the DNS message.

The SMF may use following information to create DNS message handling rules associated with a PDU Session:.

NOTE <NUM>: For example, the SMF can derive the IP address for ECS based on the N6 IP address(es) associated with serving L-PSA(s) locally configured or in the NRF.

NOTE <NUM>: Providing in DNS EDNS Client Subnet option an IP address associated with the L-PSA UPF protects the privacy of the (IP address of the) UE.

NOTE <NUM>: Option B does not support the scenario where the PSA UPF for transferring DNS Query between EASDF and DNS server, or the EASDF has no direct connectivity with the Local DNS servers.

According to at least some example embodiments, the EASDF removes the EDNS Client Subnet option from the received response message or, if it had received EDNS Client Subnet option in the DNS query message from UE, then replaces in the message from DNS server or from local DNS server, the EDNS Client Subnet option in the DNS message based on instruction from SMF or based on local configuration at the EASDF with the EDNS Client Subnet option received and removed in/from the DNS query. The SMF instructions for a matching FQDN may as well indicate EASDF to contact SMF. SMF then provides the EASDF with a DNS message handling rule;.

NOTE <NUM>: To avoid SMF overloading caused by massive reporting, the overload control mechanisms defined in clause <NUM> of TS <NUM> can be used. The information to build the EDNS Client Subnet option or the Local DNS server address provided by the SMF to the EASDF are part of the DNS message handling rules to handle DNS Queries from the UE. This information is related to DNAI(s) for that FQDN(s) for the UE location. The SMF may provide DNS message handling rules to handle DNS Queries from the UE to the EASDF when the SMF establishes the association with the EASDF for the UE and may update the rules at any time when the association exists. For the selection of the candidate DNAI for a FQDN for the UE, the SMF may consider the UE location, network topology, EAS Deployment Information and related policy information for the PDU Session provided as defined in TS <NUM>, clause <NUM> or be preconfigured into the SMF. After the UE mobility, if the provided Information for EDNS Client Subnet option or the Local DNS server address needs to be updated, the SMF may send an update of DNS message handling rules to the EASDF.

NOTE <NUM>: If multiple candidate DNAIs are available after considering the UE location, network topology and EAS deployment, the SMF selects one DNAI from the multiple ones based on operator's policy. For examples, the SMF can select the DNAI randomly, or based on selection weight factor if provided by AF, or select the DNAI closest to the UE location.

NOTE <NUM>: To protect the SMF (e.g. to block DOS from the EASDF), the EASDF IP address for DNS Query Request is only accessible from the UE IP address via UPF.

Once the UL CL/BP and L-PSA have been inserted, the SMF may decide that the DNS messages for the FQDN are to be handled by Local DNS resolver/server from now on. This option is further described in clause <NUM>. <NUM> of [A].

To avoid EASDF sending redundant DNS message reports triggering UL CL/BP insertion corresponding to the same DNAI, the SMF may send reporting-once control information (i.e. DNS message handling rule with DNS message detection template containing EAS IP address ranges with reporting-once indication set) to EASDF to instruct the EASDF to report only once for the DNS messages matching with the DNS message detection template of the reporting-once control information for the DNS message detection template. In addition, the SMF may instruct the EASDF not to report DNS Responses to SMF corresponding to some FQDN ranges and/or EAS IP address ranges e.g. once the UL CL/BP and L-PSA have been inserted for the corresponding EAS IP address ranges for Pre-established session breakout while there is configuration for the related EASDF reporting DNS Responses. After the removal or change of the L-PSA, the SMF may instruct the EASDF to restart the reports of the DNS messages. If the SMF, based on local configuration, decides that the interaction between EASDF and DNS Server in the DN shall go via an UPF, the SMF sends corresponding N4 rules to this UPF to instruct this UPF to forward DNS message between EASDF and the external DNS server. In this case, DNS messages between EASDF and DNS Server described in this clause are transferred via this UPF transparently.

NOTE <NUM>: Based network configuration, one UPF is used to transmit DNS signaling between EASDF and DNS servers. The N4 session between the SMF and this UPF is not related to a specific PDU Session but provides rules targeting Downlink traffic from DNS servers to the EASDF and associated with the traffic of multiple UE(s); the traffic forwarding between EASDF and this UPF is realized by IP in IP tunneling. The EASDF provides the SMF with the source address it uses to contact DNS servers and with the destination address where it expects to receive the tunneled traffic.

<FIG> illustrates an EAS discovery procedure with EASDF according to at least some example embodiments.

In step S301, a UE sends a PDU Session Establishment Request to an SMF as shown in step <NUM> of clause <NUM>. <NUM> of TS <NUM>. The SMF retrieves UE subscription information from a UDM (which may optionally include an indication on UE authorization for EAS discovery via EASDF) and checks if the UE is authorized to discover an EAS via an EASDF. If not authorized, this procedure is terminated, and the subsequent steps are skipped.

In step S302, during a PDU Session Establishment procedure, the SMF selects EASDF as described clause <NUM> of TS <NUM>. The SMF may consider the UE subscription information to select an EASDF as the DNS server of the PDU Session.

The SMF may indicate to the UE either that for the PDU Session the use of EDC functionality is allowed or that for the PDU Session the use of the EDC functionality is required.

If the SMF, based on local configuration, decides that the interaction between EASDF and DNS Server in the DN shall go via a PSA UPF, the SMF configures PSA UPF within N4 rules to forward the DNS message between EASDF and DN.

In step S303, the SMF invokes Neasdf_DNSContext_Create Request (UE IP address, SUPI, DNN, notification endpoint, (DNS message handling rules)) to the selected EASDF.

This step is performed before step <NUM> of PDU Session Establishment procedure in clause <NUM>. <NUM> of TS <NUM>.

The EASDF creates a DNS context for the PDU Session and stores the UE IP address, SUPI, the notification endpoint and potentially provided DNS message handling rule(s) into the context.

The EASDF is provisioned with the DNS message handling rule(s), before the DNS Query message is received at the EASDF or as a consequence of the DNS Query reporting.

In step S304, the EASDF invokes the service operation Neasdf_DNSContext_Create Response.

After this step, the SMF includes the IP address of the EASDF as DNS server/resolver for the UE in the PDU Session Establishment Accept message as defined in step <NUM> of clause <NUM>. <NUM> of TS <NUM>. The UE configures the EASDF as DNS server for that PDU Session.

If the UE requested to obtain UE IP address via DHCP and the SMF supports DHCP based IP address configuration, the SMF responds to the UE via DHCP response with the allocated UE IP address and/or the DNS server address containing the IP address of the EASDF.

In step S305, the SMF may invoke Neasdf_DNSContext_Update Request (EASDF Context ID, (DNS message handling rules)) to EASDF. The update may be triggered by UE mobility, e.g. when UE moves to a new location, or by a reporting by EASDF of a DNS Query with certain FQDN, or, the update may be triggered by insertion/removal of Local PSA, e.g. to update rules to handle DNS messages from the UE or by new PCC rule information.

In step S306, the EASDF responds with Neasdf_DNSContext_Update Response.

In step S307, if required (see clause <NUM>. <NUM> of [A]), the Application in the UE uses the EDC functionality as described in clause <NUM>. <NUM> of [A] to send the DNS Query to the EASDF. The UE sends a DNS Query message to the EASDF.

In step S308, if the DNS Query message matches a DNS message detection template of DNS message handling rule for reporting, the EASDF sends the DNS message report to SMF by invoking Neasdf_DNSContext_Notify Request (information from the DNS Query e.g. target FQDN of the DNS Query). The EASDF may add a DNS message identifier in the Neasdf_DNSContext_Notify. The DNS message identifier uniquely identifies the DNS message reported and is used to associate the corresponding DNS message handling rule included in Neasdf_DNSContext_Update Request with the identified DNS message. The DNS message identifier is generated by EASDF.

In step S309, the SMF responds with Neasdf_DNSContext_Notify Response.

In step S310, according to at least some example embodiments, if DNS message handling rule for the FQDN received in the report needs to be updated, e.g. provide updates to information to build/replace the EDNS Client Subnet option information, the SMF invokes Neasdf_DNSContext_Update Request (DNS message handling rules) to EASDF. If the EASDF provided a DNS message identifier, the SMF adds this DNS message identifier to the corresponding DNS message handling rule included in Neasdf_DNSContext_Update. If the EASDF did not provide a DNS message identifier, the SMF may use the DNS message type (Request) and the target FQDN to uniquely identify the DNS message.

For Option A, according to at least some example embodiments, the DNS handling rule includes corresponding IP address to be used to build/replace the EDNS Client Subnet option. For Option B, according to at least some example embodiments, the DNS handling rule includes corresponding Local DNS Server IP address and indication to remove possible EDNS Client Subnet option. Alternatively, according to at least some example embodiments, based on local configuration the EASDF may remove possible EDNS Client Subnet option. The EASDF may as well be instructed by the DNS handling rule to simply forward the DNS Query to a pre-configured DNS server/resolver.

In step S311, if the SMF provided a DNS message handling rule with DNS message identifier, the EASDF only applies the DNS message handling rule to the corresponding DNS message. The EASDF responds with Neasdf_DNSContext_Update Response.

In step S312, the EASDF handles the DNS Query message received from the UE as the following:.

If no DNS message detection template within the DNS message handling rule provided by the SMF matches the requested FQDN in the DNS Query, the EASDF may simply send a DNS Query to a pre-configured DNS server/resolver.

In step S313, the EASDF receives a DNS Response including EAS IP addresses which is determined by the DNS system and determines that a DNS Response can be sent to the UE.

In step S314, the EASDF sends DNS message reporting to the SMF by invoking Neasdf_DNSContext_Notify request including EAS information if the EAS IP address or the FQDN in the DNS Response message matches the DNS message detection template provided by the SMF. The DNS message reporting may contain multiple EAS IP address if the EASDF has received multiple EAS IP address(es) from the DNS server it has contacted. The DNS message reporting may contain the FQDN and the EDNS Client Subnet option received in the DNS Response message. The EASDF may also add DNS message identifier to the reporting. The DNS message identifier uniquely identifies the DNS response reported, and the EASDF can associate the corresponding DNS message handling rule included in Neasdf_DNSContext_Update Request with the identified DNS response. The DNS message identifier is generated by EASDF.

Per the received DNS message handling rule, the EASDF does not send the DNS Response message to the UE but waits for SMF instructions (in step S317), i.e. buffering the DNS Response message.

If the DNS Response(s) is required to be buffered and reported to the SMF, when the reporting-once control information is set, EASDF only reports to SMF once by invoking Neasdf_DNSContext_Notify request for DNS Responses matching with the DNS message detection template.

In step S315, the SMF invokes Neasdf_DNSContext_Notify Response service operation.

In step S316, the SMF may perform UL CL/BP and Local PSA selection and insert UL CL/BP and Local PSA.

Based on EAS information received from the EASDF in Neasdf_DNSContext_Notify, other UPF selection criteria, as specified in clause <NUM>. <NUM> in TS <NUM>, and possibly Service Experience or DN performance analytics for an Edge Application as described in TS <NUM>, the SMF may determine the DNAI and determine the associated N6 traffic routing information for the DNAI. The SMF may perform UL CL/BP and Local PSA selection and insertion as described in TS <NUM>. In case of UL CL, the traffic detection rules and traffic routing rules are determined by the SMF based on IP address range(s) per DNAI included in the EAS Deployment Information or according to PCC rule received from PCF or according to preconfigured information.

In step S317, the SMF invokes Neasdf_DNSContext_Update Request (DNS message handling rules). If the EASDF provided a DNS message identifier, the SMF adds this to the corresponding DNS message handling rule included in Neasdf_DNSContext_Update Request. If the EASDF did not provide a DNS message identifier, the SMF may use the DNS message type (Response) and the FQDN to uniquely identify the DNS response message.

The DNS message handling rule with the Control Action "Send the buffered DNS response(s) message to UE" indicates the EASDF to send DNS Response(s) buffered in step S314 to UE. Other DNS message handling rule may indicate the EASDF not to send further DNS Response message(s) corresponding to FQDN ranges and/or EAS IP address ranges.

In step S318, if the SMF provided a DNS message handling rule with DNS message identifier, the EASDF only applies the DNS message handling rule to the corresponding DNS response. The EASDF responds with Neasdf_DNSContext_Update Response.

In step S319, according to at least some example embodiments, if indicated to send the buffered DNS response(s) to UE in step S317, the EASDF removes the EDNS Client Subnet option from the Response, inserts that EDNS Client Subnet Option which was removed from the DNS query in step S312 and sends the DNS Response(s) to the UE.

During PDU Session Release procedure, the SMF removes the DNS context by invoking Neasdf_DNSContext_Delete service.

For the case that the DNS message is to be handled by Local DNS resolver/server, the DNS Query is routed to the Local DNS resolver/server corresponding to the DNAI where the L-PSA connects. The SMF selects the Local DNS server address based on the DNAI corresponding to the inserted local PSA, local configuration and based on EAS Deployment Information in AF request as specified in clause <NUM>. <NUM> of [A]. Based on the operator's configuration, one of the following options may apply when UL CL/BP and Local PSA have been inserted (during or after PDU Session Establishment):.

NOTE <NUM>: Option D assumes that ULCL steering is based on L4 information (i.e. DNS port number) and that ULCL has visibility of the DNS traffic (i.e. FQDN in the DNS Query message). The UPF may be instructed by the SMF to apply different forwarding of non-ciphered UL DNS traffic based on the target domain of the DNS Query. Option D requests modification of destination IP address of DNS messages. Whether this is allowed or not is subject to local regulations. Option D does not apply to DoH or DoT messages.

NOTE 1A: It is the decision of the application in the UE whether to use the EDNS Client Subnet Option or not to resolve the FQDN. If it uses the EDNS functionality, the usage of the EAS (re-)discovery procedures defined in clause <NUM>. <NUM> of [A] cannot be ensured.

<FIG> illustrates EAS discovery with local DNS server/resolver.

In step S400, a UE sends a PDU Session Establishment Request to an SMF as shown in step <NUM> of clause <NUM>. <NUM> of TS <NUM>. The SMF retrieves the UE subscription information from the UDM (which may optionally include an indication on UE authorization for EAS discovery via EASDF) and checks if the UE is authorized to discover the EAS via EASDF. If not authorized, the actions related to EASDF in this procedure are skipped.

In step S401, the SMF inserts UL CL/BP and Local PSA.

UL CL/BP/Local PSA insertion can be triggered by DNS messages as described in clause <NUM>. <NUM> of [A]. Or, the SMF may pre-establish the UL CL/BP and Local PSA before the UE sends out any DNS Query message (e.g. upon UE mobility). In this case, the SMF includes the IP address of Local DNS Server in PDU Session Establishment Accept message as in step <NUM> of clause <NUM>. <NUM> of TS <NUM> or in a network initiated PDU Session Modification procedure. The UE configures the Local DNS Server as DNS server for that PDU Session.

NOTE <NUM>: If the new DNS server address is provided to the UE, the UE can refresh all EAS(s) information (e.g. DNS cache) bound to the PDU Session, based on UE implementation.

The UL CL/BP and Local PSA are inserted or changed as described in TS <NUM>. In the case of IPv6 multi-homing, the SMF may also send an IPv6 multi-homed routing rule along with the IPv6 prefix to the UE to influence the selection of the source Prefix for the subsequent DNS Queries as described in TS <NUM>, clause <NUM>.

When the UL CL/BP and Local PSA are inserted or simultaneously changed, the SMF configure the UL CL/BP for DNS Query handling:.

Steps S402 and S403 are performed for option C:
In step S402, if the UL CL/BP and Local PSA are inserted after PDU Session Establishment, the SMF sends PDU Session Modification Command (Local DNS Server Address) to UE.

If, based on operator's policy or UE's mobility, the Local DNS Server IP address in the local Data Network needs to be notified or updated to UE, the SMF sends PDU Session Modification Command (Local DNS Server Address) to UE.

In step S403, the UE responds with PDU Session Modification Command Ack.

The UE configures the Local DNS Server as the DNS server for the PDU Session. The UE sends the following DNS Queries to the indicated Local DNS Server.

If EASDF was used as the DNS server for the PDU Session, the SMF may invoke Neasdf_DNSContext_Delete service to remove the DNS context in the EASDF.

NOTE <NUM>: The UE does not need to know that the new DNS server is "local".

For the Split-UE in the option C case, the new address of Local DNS Server cannot be provided to the TE or the TE OS from the MT, Annex C of [A] documents mitigations for this scenario.

In step S404, if required (see clause <NUM>. <NUM> of [A]), the application in the UE uses the EDC functionality as described in clause <NUM>. <NUM> of [A] to send the DNS Query to the DNS Resolver/DNS Server indicated by the SMF in Step S400. UE sends a DNS Query message. In the case of IPv6 multi-homing the UE selects the source IP prefix based on the IPv6 multi-homed routing rule provided by SMF.

In step S405, the DNS Query message is forwarded to the Local DNS Server and handled as described in following:.

NOTE <NUM>: The Local PSA can send the DNS traffic to the Local DNS Server via tunnelling or via IP address replacement. If IP address replacement is used, the SMF sends the IP address of the Local DNS Server to the Local PSA and instructs the Local PSA to modify the packet's destination IP address (corresponding to EASDF) to that of the Local DNS Server.

In step S406, the Local PSA receives DNS Response message from Local DNS server, it forwards it to the UL CL/BP and the UL CL/BP forwards the DNS Response message to UE.

NOTE <NUM>: If IP address replacement has been enforced at step S405, the Local PSA replaces the source IP address to EASDF IP according to SMF instruction.

If SMF decides to remove the UL CL/BP and Local PSA as defined in TS <NUM>, clause <NUM>. <NUM>, e.g. due to UEmobility, the SMF sends a PDU Session Modification Command to configure the new address of the DNS server on UE (e.g. to set it to the address of EASDF).

Now reference is made to <FIG> illustrating a simplified block diagram of control units <NUM>, <NUM> that are suitable for use in practicing at least some example embodiments. According to an implementation example, process <NUM> illustrated in <FIG> is implemented by the control unit <NUM>, and process <NUM> illustrated in <FIG> is implemented by the control unit <NUM>.

The control units <NUM>, <NUM> comprise processing resources (e.g. processing circuitry) <NUM>, <NUM>, memory resources (e.g. memory circuitry) <NUM>, <NUM> and interfaces (e.g. interface circuitry) <NUM>, <NUM>, which are coupled via a wired or wireless connection <NUM>, <NUM>.

The control unit <NUM> is coupled via its interfaces <NUM> to the control unit <NUM> through a wired or wireless connection <NUM>. The control unit <NUM> is coupled via its interfaces <NUM> to the control unit <NUM> through the wired or wireless connection <NUM>.

According to an example implementation, the memory resources <NUM>, <NUM> are of any type suitable to the local technical environment and are implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The processing resources <NUM>, <NUM> are of any type suitable to the local technical environment, and include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi core processor architecture, as non-limiting examples.

According to an implementation example, the memory resources <NUM>, <NUM> comprise one or more non-transitory computer-readable storage media which store one or more programs that when executed by the processing resources <NUM>, <NUM> cause the control unit <NUM>, <NUM> to function as first network entity or second network entity as described above.

Further, as used in this application, the term "circuitry" may refer to one or more or all of the following:.

The term "non-transitory", as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

Claim 1:
A method for use by an edge application server discovery function, EASDF, of a communication network, the method comprising:
receiving a domain name server, DNS, query from a user equipment, the DNS query including a first subnet option;
in accordance with a first handling rule, processing the DNS query by replacing the first subnet option by a second subnet option different from the first subnet option, and forwarding the processed DNS query to a domain name server;
receiving a DNS response from the domain name server, wherein the DNS response includes a response to the DNS query and is related to the second subnet option;
in accordance with a second handling rule, processing the DNS response by replacing the second subnet option by the first subnet option, and forwarding the processed DNS response to the user equipment.